first commit

core/modules/comment/tests/modules/comment_base_field_test/comment_base_field_test.info.yml

@@ -0,0 +1,13 @@
+name: 'Comment base field test'
+type: module
+description: 'Test comment as a base field'
+package: Testing
+# version: VERSION
+dependencies:
+  - drupal:comment
+  - drupal:entity_test
+
+# Information added by Drupal.org packaging script on 2024-07-04
+version: '10.3.1'
+project: 'drupal'
+datestamp: 1720094222

core/modules/comment/tests/modules/comment_base_field_test/src/Entity/CommentTestBaseField.php

@@ -0,0 +1,39 @@
+<?php
+
+namespace Drupal\comment_base_field_test\Entity;
+
+use Drupal\comment\Plugin\Field\FieldType\CommentItemInterface;
+use Drupal\Core\Entity\EntityTypeInterface;
+use Drupal\Core\Field\BaseFieldDefinition;
+use Drupal\entity_test\Entity\EntityTest;
+
+/**
+ * Defines a test entity class for comment as a base field.
+ *
+ * @ContentEntityType(
+ *   id = "comment_test_base_field",
+ *   label = @Translation("Test comment - base field"),
+ *   base_table = "comment_test_base_field",
+ *   entity_keys = {
+ *     "id" = "id",
+ *     "uuid" = "uuid",
+ *     "bundle" = "type"
+ *   },
+ * )
+ */
+class CommentTestBaseField extends EntityTest {
+
+  public static function baseFieldDefinitions(EntityTypeInterface $entity_type) {
+    $fields = parent::baseFieldDefinitions($entity_type);
+
+    $fields['test_comment'] = BaseFieldDefinition::create('comment')
+      ->setLabel(t('A comment field'))
+      ->setSetting('comment_type', 'test_comment_type')
+      ->setDefaultValue([
+        'status' => CommentItemInterface::OPEN,
+      ]);
+
+    return $fields;
+  }
+
+}

core/modules/comment/tests/modules/comment_display_configurable_test/comment_display_configurable_test.info.yml

@@ -0,0 +1,10 @@
+name: 'Comment configurable display module tests'
+type: module
+description: 'Support module for comment \Drupal\Core\Field\BaseFieldDefinition::setDisplayConfigurable() testing.'
+package: Testing
+# version: VERSION
+
+# Information added by Drupal.org packaging script on 2024-07-04
+version: '10.3.1'
+project: 'drupal'
+datestamp: 1720094222

core/modules/comment/tests/modules/comment_display_configurable_test/comment_display_configurable_test.module

@@ -0,0 +1,28 @@
+<?php
+
+/**
+ * @file
+ * A module for testing making comment base fields' displays configurable.
+ */
+
+use Drupal\Core\Entity\EntityTypeInterface;
+
+/**
+ * Implements hook_entity_base_field_info_alter().
+ */
+function comment_display_configurable_test_entity_base_field_info_alter(&$base_field_definitions, EntityTypeInterface $entity_type) {
+  if ($entity_type->id() == 'comment') {
+    foreach (['created', 'uid', 'pid', 'subject'] as $field) {
+      /** @var \Drupal\Core\Field\BaseFieldDefinition[] $base_field_definitions */
+      $base_field_definitions[$field]->setDisplayConfigurable('view', TRUE);
+    }
+  }
+}
+
+/**
+ * Implements hook_entity_type_build().
+ */
+function comment_display_configurable_test_entity_type_build(array &$entity_types) {
+  // Allow skipping of extra preprocessing for configurable display.
+  $entity_types['comment']->set('enable_base_field_custom_preprocess_skipping', TRUE);
+}

core/modules/comment/tests/modules/comment_empty_title_test/comment_empty_title_test.info.yml

@@ -0,0 +1,12 @@
+name: 'Comment empty titles test'
+type: module
+description: 'Support module for testing empty title accessibility with Comment module.'
+package: Testing
+# version: VERSION
+dependencies:
+  - drupal:comment
+
+# Information added by Drupal.org packaging script on 2024-07-04
+version: '10.3.1'
+project: 'drupal'
+datestamp: 1720094222

core/modules/comment/tests/modules/comment_empty_title_test/comment_empty_title_test.module

@@ -0,0 +1,13 @@
+<?php
+
+/**
+ * @file
+ * Empties comment titles to test markup in edge case scenarios.
+ */
+
+/**
+ * Implements hook_preprocess_comment().
+ */
+function comment_empty_title_test_preprocess_comment(&$variables) {
+  $variables['title'] = '';
+}

core/modules/comment/tests/modules/comment_test/comment_test.info.yml

@@ -0,0 +1,12 @@
+name: 'Comment test'
+type: module
+description: 'Support module for Comment module testing.'
+package: Testing
+# version: VERSION
+dependencies:
+  - drupal:comment
+
+# Information added by Drupal.org packaging script on 2024-07-04
+version: '10.3.1'
+project: 'drupal'
+datestamp: 1720094222

core/modules/comment/tests/modules/comment_test/comment_test.module

@@ -0,0 +1,43 @@
+<?php
+
+/**
+ * @file
+ * Implements comment-related hooks to test API interactions.
+ */
+
+use Drupal\comment\CommentInterface;
+use Drupal\Core\Url;
+
+/**
+ * Implements hook_entity_type_alter().
+ */
+function comment_test_entity_type_alter(array &$entity_types) {
+  /** @var \Drupal\Core\Entity\EntityTypeInterface[] $entity_types */
+  if (\Drupal::languageManager()->isMultilingual()) {
+    // Enable language handling for comment fields.
+    $translation = $entity_types['comment']->get('translation');
+    $translation['comment_test'] = TRUE;
+    $entity_types['comment']->set('translation', $translation);
+  }
+}
+
+/**
+ * Implements hook_comment_links_alter().
+ */
+function comment_test_comment_links_alter(array &$links, CommentInterface &$entity, array &$context) {
+  // Allow tests to enable or disable this alter hook.
+  if (!\Drupal::state()->get('comment_test_links_alter_enabled', FALSE)) {
+    return;
+  }
+
+  $links['comment_test'] = [
+    '#theme' => 'links__comment__comment_test',
+    '#attributes' => ['class' => ['links', 'inline']],
+    '#links' => [
+      'comment-report' => [
+        'title' => t('Report'),
+        'url' => Url::fromRoute('comment_test.report', ['comment' => $entity->id()], ['query' => ['token' => \Drupal::getContainer()->get('csrf_token')->get("comment/{$entity->id()}/report")]]),
+      ],
+    ],
+  ];
+}

core/modules/comment/tests/modules/comment_test/comment_test.routing.yml

@@ -0,0 +1,8 @@
+comment_test.report:
+  path: '/comment/{comment}/report'
+  defaults:
+    _title: 'Report'
+    _controller: '\Drupal\comment_test\Controller\CommentTestController::commentReport'
+  requirements:
+    _access: 'TRUE'
+    _csrf_token: 'TRUE'

core/modules/comment/tests/modules/comment_test/src/Controller/CommentTestController.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace Drupal\comment_test\Controller;
+
+use Drupal\comment\CommentInterface;
+use Drupal\Core\Controller\ControllerBase;
+
+/**
+ * Controller for the comment_test.module.
+ */
+class CommentTestController extends ControllerBase {
+
+  /**
+   * Provides a comment report.
+   */
+  public function commentReport(CommentInterface $comment) {
+    return ['#markup' => $this->t('Report for a comment')];
+  }
+
+}

core/modules/comment/tests/modules/comment_test_views/comment_test_views.info.yml

@@ -0,0 +1,13 @@
+name: 'Comment test views'
+type: module
+description: 'Provides default views for views comment tests.'
+package: Testing
+# version: VERSION
+dependencies:
+  - drupal:comment
+  - drupal:views
+
+# Information added by Drupal.org packaging script on 2024-07-04
+version: '10.3.1'
+project: 'drupal'
+datestamp: 1720094222

core/modules/comment/tests/modules/comment_test_views/test_views/views.view.test_comment.yml

@@ -0,0 +1,42 @@
+langcode: en
+status: true
+dependencies:
+  module:
+    - comment
+    - entity_test
+    - user
+id: test_comment
+label: test_comment
+module: views
+description: ''
+tag: ''
+base_table: comment_field_data
+base_field: cid
+display:
+  default:
+    display_plugin: default
+    display_title: Default
+    id: default
+    position: 0
+    display_options:
+      defaults:
+        fields: false
+        pager: false
+        sorts: false
+      row:
+        type: fields
+      fields:
+        subject:
+          id: subject
+          table: comment_field_data
+          field: subject
+          label: ''
+          type: string
+          plugin_id: field
+          entity_type: comment
+          entity_field: subject
+      pager:
+        options:
+          offset: 0
+        type: none
+      sorts: {  }

core/modules/comment/tests/modules/comment_test_views/test_views/views.view.test_comment_count.yml

@@ -0,0 +1,244 @@
+langcode: en
+status: true
+dependencies:
+  module:
+    - node
+    - user
+id: test_comment_count
+label: 'test comment count'
+module: views
+description: ''
+tag: ''
+base_table: node_field_data
+base_field: nid
+display:
+  default:
+    display_plugin: default
+    id: default
+    display_title: Default
+    position: 0
+    display_options:
+      access:
+        type: perm
+        options:
+          perm: 'access content'
+      cache:
+        type: tag
+        options: {  }
+      query:
+        type: views_query
+        options:
+          disable_sql_rewrite: false
+          distinct: false
+          replica: false
+          query_comment: ''
+          query_tags: {  }
+      exposed_form:
+        type: basic
+        options:
+          submit_button: Apply
+          reset_button: false
+          reset_button_label: Reset
+          exposed_sorts_label: 'Sort by'
+          expose_sort_order: true
+          sort_asc_label: Asc
+          sort_desc_label: Desc
+      pager:
+        type: mini
+        options:
+          items_per_page: 10
+          offset: 0
+          id: 0
+          total_pages: null
+          expose:
+            items_per_page: false
+            items_per_page_label: 'Items per page'
+            items_per_page_options: '5, 10, 25, 50'
+            items_per_page_options_all: false
+            items_per_page_options_all_label: '- All -'
+            offset: false
+            offset_label: Offset
+          tags:
+            previous: ‹‹
+            next: ››
+      style:
+        type: default
+        options:
+          grouping: {  }
+          row_class: ''
+          default_row_class: true
+          uses_fields: false
+      row:
+        type: fields
+        options:
+          inline: {  }
+          separator: ''
+          hide_empty: false
+          default_field_elements: true
+      fields:
+        title:
+          id: title
+          table: node_field_data
+          field: title
+          entity_type: node
+          entity_field: title
+          label: ''
+          alter:
+            alter_text: false
+            make_link: false
+            absolute: false
+            trim: false
+            word_boundary: false
+            ellipsis: false
+            strip_tags: false
+            html: false
+          hide_empty: false
+          empty_zero: false
+          settings:
+            link_to_entity: true
+          plugin_id: field
+          relationship: none
+          group_type: group
+          admin_label: ''
+          exclude: false
+          element_type: ''
+          element_class: ''
+          element_label_type: ''
+          element_label_class: ''
+          element_label_colon: true
+          element_wrapper_type: ''
+          element_wrapper_class: ''
+          element_default_classes: true
+          empty: ''
+          hide_alter_empty: true
+          click_sort_column: value
+          type: string
+          group_column: value
+          group_columns: {  }
+          group_rows: true
+          delta_limit: 0
+          delta_offset: 0
+          delta_reversed: false
+          delta_first_last: false
+          multi_type: separator
+          separator: ', '
+          field_api_classes: false
+        comment_count:
+          id: comment_count
+          table: comment_entity_statistics
+          field: comment_count
+          relationship: none
+          group_type: group
+          admin_label: ''
+          label: ''
+          exclude: false
+          alter:
+            alter_text: false
+            text: ''
+            make_link: false
+            path: ''
+            absolute: false
+            external: false
+            replace_spaces: false
+            path_case: none
+            trim_whitespace: false
+            alt: ''
+            rel: ''
+            link_class: ''
+            prefix: ''
+            suffix: ''
+            target: ''
+            nl2br: false
+            max_length: 0
+            word_boundary: true
+            ellipsis: true
+            more_link: false
+            more_link_text: ''
+            more_link_path: ''
+            strip_tags: false
+            trim: false
+            preserve_tags: ''
+            html: false
+          element_type: ''
+          element_class: ''
+          element_label_type: ''
+          element_label_class: ''
+          element_label_colon: false
+          element_wrapper_type: ''
+          element_wrapper_class: ''
+          element_default_classes: true
+          empty: ''
+          hide_empty: false
+          empty_zero: false
+          hide_alter_empty: true
+          set_precision: false
+          precision: 0
+          decimal: .
+          separator: ''
+          format_plural: false
+          format_plural_string: !!binary MQNAY291bnQ=
+          prefix: ''
+          suffix: ''
+          plugin_id: numeric
+      filters:
+        status:
+          value: '1'
+          table: node_field_data
+          field: status
+          plugin_id: boolean
+          entity_type: node
+          entity_field: status
+          id: status
+          expose:
+            operator: ''
+            operator_limit_selection: false
+            operator_list: {  }
+          group: 1
+      sorts:
+        created:
+          id: created
+          table: node_field_data
+          field: created
+          order: DESC
+          entity_type: node
+          entity_field: created
+          plugin_id: date
+          relationship: none
+          group_type: group
+          admin_label: ''
+          exposed: false
+          expose:
+            label: ''
+          granularity: second
+      header: {  }
+      footer: {  }
+      empty: {  }
+      relationships: {  }
+      arguments: {  }
+      display_extenders: {  }
+    cache_metadata:
+      max-age: -1
+      contexts:
+        - 'languages:language_content'
+        - 'languages:language_interface'
+        - url.query_args
+        - 'user.node_grants:view'
+        - user.permissions
+      tags: {  }
+  page_1:
+    display_plugin: page
+    id: page_1
+    display_title: Page
+    position: 1
+    display_options:
+      display_extenders: {  }
+      path: test-comment-count
+    cache_metadata:
+      max-age: -1
+      contexts:
+        - 'languages:language_content'
+        - 'languages:language_interface'
+        - url.query_args
+        - 'user.node_grants:view'
+        - user.permissions
+      tags: {  }

core/modules/comment/tests/modules/comment_test_views/test_views/views.view.test_comment_field_name.yml

@@ -0,0 +1,202 @@
+langcode: en
+status: true
+dependencies:
+  module:
+    - comment
+    - user
+id: test_comment_field_name
+label: 'Comment field name test'
+module: views
+description: ''
+tag: ''
+base_table: comment_field_data
+base_field: cid
+display:
+  default:
+    display_plugin: default
+    id: default
+    display_title: Default
+    position: 0
+    display_options:
+      access:
+        type: perm
+        options:
+          perm: 'access comments'
+      cache:
+        type: tag
+        options: {  }
+      query:
+        type: views_query
+        options:
+          disable_sql_rewrite: false
+          distinct: false
+          replica: false
+          query_comment: ''
+          query_tags: {  }
+      exposed_form:
+        type: basic
+        options:
+          submit_button: Apply
+          reset_button: false
+          reset_button_label: Reset
+          exposed_sorts_label: 'Sort by'
+          expose_sort_order: true
+          sort_asc_label: Asc
+          sort_desc_label: Desc
+      pager:
+        type: full
+        options:
+          items_per_page: 10
+          offset: 0
+          id: 0
+          total_pages: null
+          expose:
+            items_per_page: false
+            items_per_page_label: 'Items per page'
+            items_per_page_options: '5, 10, 25, 50'
+            items_per_page_options_all: false
+            items_per_page_options_all_label: '- All -'
+            offset: false
+            offset_label: Offset
+          tags:
+            previous: '‹ Previous'
+            next: 'Next ›'
+            first: '« First'
+            last: 'Last »'
+          quantity: 9
+      style:
+        type: default
+      row:
+        type: fields
+      relationships: {  }
+      fields:
+        field_name:
+          id: field_name
+          table: comment_field_data
+          field: field_name
+          relationship: none
+          group_type: group
+          admin_label: ''
+          label: ''
+          exclude: false
+          alter:
+            alter_text: false
+            text: ''
+            make_link: false
+            path: ''
+            absolute: false
+            external: false
+            replace_spaces: false
+            path_case: none
+            trim_whitespace: false
+            alt: ''
+            rel: ''
+            link_class: ''
+            prefix: ''
+            suffix: ''
+            target: ''
+            nl2br: false
+            max_length: 0
+            word_boundary: true
+            ellipsis: true
+            more_link: false
+            more_link_text: ''
+            more_link_path: ''
+            strip_tags: false
+            trim: false
+            preserve_tags: ''
+            html: false
+          element_type: ''
+          element_class: ''
+          element_label_type: ''
+          element_label_class: ''
+          element_label_colon: false
+          element_wrapper_type: ''
+          element_wrapper_class: ''
+          element_default_classes: true
+          empty: ''
+          hide_empty: false
+          empty_zero: false
+          hide_alter_empty: true
+          click_sort_column: value
+          type: string
+          settings:
+            link_to_entity: false
+          group_column: value
+          group_columns: {  }
+          group_rows: true
+          delta_limit: 0
+          delta_offset: 0
+          delta_reversed: false
+          delta_first_last: false
+          multi_type: separator
+          separator: ', '
+          field_api_classes: false
+          entity_type: comment
+          entity_field: field_name
+          plugin_id: field
+      filters:
+        field_name:
+          id: field_name
+          table: comment_field_data
+          field: field_name
+          relationship: none
+          group_type: group
+          admin_label: ''
+          operator: starts
+          value: comment
+          group: 1
+          exposed: false
+          expose:
+            operator_id: ''
+            label: ''
+            description: ''
+            use_operator: false
+            operator: ''
+            identifier: ''
+            required: false
+            remember: false
+            multiple: false
+            remember_roles:
+              authenticated: authenticated
+          is_grouped: false
+          group_info:
+            label: ''
+            description: ''
+            identifier: ''
+            optional: true
+            widget: select
+            multiple: false
+            remember: false
+            default_group: All
+            default_group_multiple: {  }
+            group_items: {  }
+          entity_type: comment
+          entity_field: field_name
+          plugin_id: string
+      sorts:
+        field_name:
+          id: field_name
+          table: comment_field_data
+          field: field_name
+          relationship: none
+          group_type: group
+          admin_label: ''
+          order: ASC
+          exposed: false
+          expose:
+            label: ''
+          entity_type: comment
+          entity_field: field_name
+          plugin_id: standard
+      title: 'Comment Field Name test'
+      header: {  }
+      footer: {  }
+      empty: {  }
+      arguments: {  }
+      display_extenders: {  }
+    cache_metadata:
+      contexts:
+        - languages
+        - user
+      max-age: 0

core/modules/comment/tests/modules/comment_test_views/test_views/views.view.test_comment_operations.yml

@@ -0,0 +1,253 @@
+langcode: en
+status: true
+dependencies:
+  module:
+    - comment
+    - user
+id: test_comment_operations
+label: test_comment_operations
+module: views
+description: ''
+tag: ''
+base_table: comment_field_data
+base_field: cid
+display:
+  default:
+    display_plugin: default
+    id: default
+    display_title: Default
+    position: 0
+    display_options:
+      access:
+        type: perm
+        options:
+          perm: 'administer comments'
+      cache:
+        type: tag
+        options: {  }
+      query:
+        type: views_query
+        options:
+          disable_sql_rewrite: false
+          distinct: false
+          replica: false
+          query_comment: ''
+          query_tags: {  }
+      exposed_form:
+        type: basic
+        options:
+          submit_button: Apply
+          reset_button: false
+          reset_button_label: Reset
+          exposed_sorts_label: 'Sort by'
+          expose_sort_order: true
+          sort_asc_label: Asc
+          sort_desc_label: Desc
+      pager:
+        type: full
+        options:
+          items_per_page: 10
+          offset: 0
+          id: 0
+          total_pages: null
+          expose:
+            items_per_page: false
+            items_per_page_label: 'Items per page'
+            items_per_page_options: '5, 10, 25, 50'
+            items_per_page_options_all: false
+            items_per_page_options_all_label: '- All -'
+            offset: false
+            offset_label: Offset
+          tags:
+            previous: '‹ Previous'
+            next: 'Next ›'
+            first: '« First'
+            last: 'Last »'
+          quantity: 9
+      style:
+        type: table
+        options:
+          grouping: {  }
+          row_class: ''
+          default_row_class: true
+          override: true
+          sticky: false
+          caption: ''
+          summary: ''
+          description: ''
+          columns:
+            subject: subject
+            operations: operations
+          info:
+            subject:
+              sortable: false
+              default_sort_order: asc
+              align: ''
+              separator: ''
+              empty_column: false
+              responsive: ''
+            operations:
+              sortable: false
+              default_sort_order: asc
+              align: ''
+              separator: ''
+              empty_column: false
+              responsive: ''
+          default: '-1'
+          empty_table: false
+      row:
+        type: fields
+        options:
+          inline: {  }
+          separator: ''
+          hide_empty: false
+          default_field_elements: true
+      relationships: {  }
+      fields:
+        subject:
+          id: subject
+          table: comment_field_data
+          field: subject
+          relationship: none
+          group_type: group
+          admin_label: ''
+          label: Subject
+          exclude: false
+          alter:
+            alter_text: false
+            text: ''
+            make_link: false
+            path: ''
+            absolute: false
+            external: false
+            replace_spaces: false
+            path_case: none
+            trim_whitespace: false
+            alt: ''
+            rel: ''
+            link_class: ''
+            prefix: ''
+            suffix: ''
+            target: ''
+            nl2br: false
+            max_length: 0
+            word_boundary: false
+            ellipsis: false
+            more_link: false
+            more_link_text: ''
+            more_link_path: ''
+            strip_tags: false
+            trim: false
+            preserve_tags: ''
+            html: false
+          element_type: ''
+          element_class: ''
+          element_label_type: ''
+          element_label_class: ''
+          element_label_colon: true
+          element_wrapper_type: ''
+          element_wrapper_class: ''
+          element_default_classes: true
+          empty: ''
+          hide_empty: false
+          empty_zero: false
+          hide_alter_empty: true
+          click_sort_column: value
+          type: string
+          settings:
+            link_to_entity: true
+          group_column: value
+          group_columns: {  }
+          group_rows: true
+          delta_limit: 0
+          delta_offset: 0
+          delta_reversed: false
+          delta_first_last: false
+          multi_type: separator
+          separator: ', '
+          field_api_classes: false
+          entity_type: comment
+          entity_field: subject
+          plugin_id: field
+        operations:
+          id: operations
+          table: comment
+          field: operations
+          relationship: none
+          group_type: group
+          admin_label: ''
+          label: Operations
+          exclude: false
+          alter:
+            alter_text: false
+            text: ''
+            make_link: false
+            path: ''
+            absolute: false
+            external: false
+            replace_spaces: false
+            path_case: none
+            trim_whitespace: false
+            alt: ''
+            rel: ''
+            link_class: ''
+            prefix: ''
+            suffix: ''
+            target: ''
+            nl2br: false
+            max_length: 0
+            word_boundary: true
+            ellipsis: true
+            more_link: false
+            more_link_text: ''
+            more_link_path: ''
+            strip_tags: false
+            trim: false
+            preserve_tags: ''
+            html: false
+          element_type: ''
+          element_class: ''
+          element_label_type: ''
+          element_label_class: ''
+          element_label_colon: false
+          element_wrapper_type: ''
+          element_wrapper_class: ''
+          element_default_classes: true
+          empty: ''
+          hide_empty: false
+          empty_zero: false
+          hide_alter_empty: true
+          destination: true
+          entity_type: comment
+          plugin_id: entity_operations
+      filters: {  }
+      sorts: {  }
+      header: {  }
+      footer: {  }
+      empty: {  }
+      arguments: {  }
+      display_extenders: {  }
+    cache_metadata:
+      max-age: 0
+      contexts:
+        - 'languages:language_content'
+        - 'languages:language_interface'
+        - url.query_args
+        - user.permissions
+      tags: {  }
+  page_1:
+    display_plugin: page
+    id: page_1
+    display_title: Page
+    position: 1
+    display_options:
+      display_extenders: {  }
+      path: test-comment-operations
+    cache_metadata:
+      max-age: 0
+      contexts:
+        - 'languages:language_content'
+        - 'languages:language_interface'
+        - url.query_args
+        - user.permissions
+      tags: {  }

core/modules/comment/tests/modules/comment_test_views/test_views/views.view.test_comment_row.yml

@@ -0,0 +1,156 @@
+langcode: en
+status: true
+dependencies:
+  module:
+    - comment
+    - node
+    - user
+id: test_comment_row
+label: test_comment_row
+module: views
+description: ''
+tag: ''
+base_table: comment_field_data
+base_field: cid
+display:
+  default:
+    display_plugin: default
+    id: default
+    display_title: Default
+    position: 1
+    display_options:
+      access:
+        type: perm
+        options:
+          perm: 'access content'
+      cache:
+        type: tag
+        options: {  }
+      query:
+        type: views_query
+        options:
+          disable_sql_rewrite: false
+          distinct: false
+          replica: false
+          query_comment: ''
+          query_tags: {  }
+      exposed_form:
+        type: basic
+        options:
+          submit_button: Apply
+          reset_button: false
+          reset_button_label: Reset
+          exposed_sorts_label: 'Sort by'
+          expose_sort_order: true
+          sort_asc_label: Asc
+          sort_desc_label: Desc
+      pager:
+        type: full
+        options:
+          items_per_page: 10
+          offset: 0
+          id: 0
+          total_pages: null
+          expose:
+            items_per_page: false
+            items_per_page_label: 'Items per page'
+            items_per_page_options: '5, 10, 25, 50'
+            items_per_page_options_all: false
+            items_per_page_options_all_label: '- All -'
+            offset: false
+            offset_label: Offset
+          tags:
+            previous: '‹ Previous'
+            next: 'Next ›'
+            first: '« First'
+            last: 'Last »'
+          quantity: 9
+      style:
+        type: default
+      row:
+        type: 'entity:comment'
+        options:
+          view_mode: full
+      relationships:
+        node:
+          field: node
+          id: node
+          required: true
+          table: comment_field_data
+          relationship: none
+          group_type: group
+          admin_label: Content
+      fields:
+        subject:
+          id: subject
+          table: comment_field_data
+          field: subject
+          label: ''
+          alter:
+            alter_text: false
+            make_link: false
+            absolute: false
+            trim: false
+            word_boundary: false
+            ellipsis: false
+            strip_tags: false
+            html: false
+          hide_empty: false
+          empty_zero: false
+          relationship: none
+          group_type: group
+          admin_label: ''
+          exclude: false
+          element_type: ''
+          element_class: ''
+          element_label_type: ''
+          element_label_class: ''
+          element_label_colon: true
+          element_wrapper_type: ''
+          element_wrapper_class: ''
+          element_default_classes: true
+          empty: ''
+          hide_alter_empty: true
+          type: string
+          settings:
+            link_to_entity: true
+          plugin_id: field
+          entity_type: comment
+          entity_field: subject
+      filters:
+        status:
+          value: '1'
+          table: comment_field_data
+          field: status
+          id: status
+          expose:
+            operator: ''
+          group: 1
+          plugin_id: boolean
+          entity_type: comment
+          entity_field: status
+        status_node:
+          value: '1'
+          table: node_field_data
+          field: status
+          relationship: node
+          id: status_node
+          expose:
+            operator: ''
+          group: 1
+          plugin_id: boolean
+          entity_type: node
+          entity_field: status
+      sorts: {  }
+      title: test_comment_row
+      header: {  }
+      footer: {  }
+      empty: {  }
+      arguments: {  }
+  page_1:
+    display_plugin: page
+    id: page_1
+    display_title: Page
+    position: 1
+    display_options:
+      path: test-comment-row

core/modules/comment/tests/modules/comment_test_views/test_views/views.view.test_comment_rss.yml

@@ -0,0 +1,78 @@
+langcode: en
+status: true
+dependencies:
+  module:
+    - comment
+    - node
+    - user
+id: test_comment_rss
+label: test_comment_rss
+module: views
+description: ''
+tag: ''
+base_table: comment_field_data
+base_field: cid
+display:
+  default:
+    display_plugin: default
+    id: default
+    display_title: Default
+    position: null
+    display_options:
+      access:
+        type: perm
+      cache:
+        type: tag
+      query:
+        type: views_query
+      exposed_form:
+        type: basic
+      pager:
+        type: full
+      style:
+        type: default
+      row:
+        type: fields
+      relationships:
+        node:
+          field: node
+          id: node
+          required: true
+          table: comment_field_data
+      fields:
+        subject:
+          id: subject
+          table: comment_field_data
+          field: subject
+          plugin_id: field
+          label: ''
+          alter:
+            alter_text: false
+            make_link: false
+            absolute: false
+            trim: false
+            word_boundary: false
+            ellipsis: false
+            strip_tags: false
+            html: false
+          hide_empty: false
+          empty_zero: false
+          type: string
+          settings:
+            link_to_entity: true
+          entity_type: comment
+          entity_field: subject
+      filters: {  }
+      sorts: {  }
+  feed_1:
+    display_plugin: feed
+    id: feed_1
+    display_title: Feed
+    position: null
+    display_options:
+      path: test-comment-rss
+      defaults:
+        row: false
+      row:
+        type: comment_rss
+        options: {}

core/modules/comment/tests/modules/comment_test_views/test_views/views.view.test_comment_schema.yml

@@ -0,0 +1,301 @@
+langcode: en
+status: true
+dependencies:
+  module:
+    - comment
+    - user
+id: test_comment_schema
+label: Comments
+module: comment
+description: 'Find and manage comments.'
+tag: default
+base_table: comment_field_data
+base_field: cid
+display:
+  default:
+    id: default
+    display_title: Default
+    display_plugin: default
+    position: 0
+    display_options:
+      title: Comments
+      fields:
+        subject:
+          id: subject
+          table: comment_field_data
+          field: subject
+          relationship: none
+          group_type: group
+          admin_label: ''
+          entity_type: comment
+          entity_field: subject
+          plugin_id: field
+          label: Title
+          exclude: false
+          alter:
+            alter_text: false
+            text: ''
+            make_link: false
+            path: ''
+            absolute: false
+            external: false
+            replace_spaces: false
+            path_case: none
+            trim_whitespace: false
+            alt: ''
+            rel: ''
+            link_class: ''
+            prefix: ''
+            suffix: ''
+            target: ''
+            nl2br: false
+            max_length: 0
+            word_boundary: true
+            ellipsis: true
+            more_link: false
+            more_link_text: ''
+            more_link_path: ''
+            strip_tags: false
+            trim: false
+            preserve_tags: ''
+            html: false
+          element_type: ''
+          element_class: ''
+          element_label_type: ''
+          element_label_class: ''
+          element_label_colon: true
+          element_wrapper_type: ''
+          element_wrapper_class: ''
+          element_default_classes: true
+          empty: ''
+          hide_empty: false
+          empty_zero: false
+          hide_alter_empty: true
+          click_sort_column: value
+          type: comment_permalink
+          settings:
+            link_to_entity: false
+          group_column: value
+          group_columns: {  }
+          group_rows: true
+          delta_limit: 0
+          delta_offset: 0
+          delta_reversed: false
+          delta_first_last: false
+          multi_type: separator
+          separator: ', '
+          field_api_classes: false
+        approve_comment:
+          id: approve_comment
+          table: comment
+          field: approve_comment
+          relationship: none
+          group_type: group
+          admin_label: ''
+          entity_type: comment
+          plugin_id: comment_link_approve
+          label: 'Link to approve comment'
+          exclude: false
+          alter:
+            alter_text: false
+            text: ''
+            make_link: false
+            path: ''
+            absolute: false
+            external: false
+            replace_spaces: false
+            path_case: none
+            trim_whitespace: false
+            alt: ''
+            rel: ''
+            link_class: ''
+            prefix: ''
+            suffix: ''
+            target: ''
+            nl2br: false
+            max_length: 0
+            word_boundary: true
+            ellipsis: true
+            more_link: false
+            more_link_text: ''
+            more_link_path: ''
+            strip_tags: false
+            trim: false
+            preserve_tags: ''
+            html: false
+          element_type: ''
+          element_class: ''
+          element_label_type: ''
+          element_label_class: ''
+          element_label_colon: true
+          element_wrapper_type: ''
+          element_wrapper_class: ''
+          element_default_classes: true
+          empty: ''
+          hide_empty: false
+          empty_zero: false
+          hide_alter_empty: true
+          text: Approve
+        status:
+          id: status
+          table: comment_field_data
+          field: status
+          relationship: none
+          group_type: group
+          admin_label: ''
+          entity_type: comment
+          entity_field: status
+          plugin_id: field
+          label: 'Approved status'
+          exclude: false
+          alter:
+            alter_text: false
+            text: ''
+            make_link: false
+            path: ''
+            absolute: false
+            external: false
+            replace_spaces: false
+            path_case: none
+            trim_whitespace: false
+            alt: ''
+            rel: ''
+            link_class: ''
+            prefix: ''
+            suffix: ''
+            target: ''
+            nl2br: false
+            max_length: 0
+            word_boundary: true
+            ellipsis: true
+            more_link: false
+            more_link_text: ''
+            more_link_path: ''
+            strip_tags: false
+            trim: false
+            preserve_tags: ''
+            html: false
+          element_type: ''
+          element_class: ''
+          element_label_type: ''
+          element_label_class: ''
+          element_label_colon: true
+          element_wrapper_type: ''
+          element_wrapper_class: ''
+          element_default_classes: true
+          empty: ''
+          hide_empty: false
+          empty_zero: false
+          hide_alter_empty: true
+          click_sort_column: value
+          type: boolean
+          settings:
+            format: yes-no
+            format_custom_false: ''
+            format_custom_true: Approved
+          group_column: value
+          group_columns: {  }
+          group_rows: true
+          delta_limit: 0
+          delta_offset: 0
+          delta_reversed: false
+          delta_first_last: false
+          multi_type: separator
+          separator: ', '
+          field_api_classes: false
+      pager:
+        type: none
+        options:
+          offset: 0
+      exposed_form:
+        type: basic
+        options:
+          submit_button: Filter
+          reset_button: false
+          reset_button_label: Reset
+          exposed_sorts_label: 'Sort by'
+          expose_sort_order: true
+          sort_asc_label: Asc
+          sort_desc_label: Desc
+      access:
+        type: perm
+        options:
+          perm: 'administer comments'
+      cache:
+        type: none
+        options: {  }
+      empty: {  }
+      sorts: {  }
+      arguments: {  }
+      filters: {  }
+      filter_groups:
+        operator: AND
+        groups: {  }
+      style:
+        type: table
+        options:
+          grouping: {  }
+          row_class: ''
+          default_row_class: false
+          columns:
+            approve_comment: approve_comment
+          default: '-1'
+          info:
+            approve_comment:
+              sortable: false
+              default_sort_order: asc
+              align: ''
+              separator: ''
+              empty_column: false
+              responsive: ''
+          override: false
+          sticky: false
+          summary: ''
+          empty_table: false
+          caption: ''
+          description: ''
+      row:
+        type: fields
+      query:
+        type: views_query
+        options:
+          query_comment: ''
+          disable_sql_rewrite: false
+          distinct: false
+          replica: false
+          query_tags: {  }
+      relationships: {  }
+      css_class: ''
+      use_ajax: false
+      group_by: false
+      show_admin_links: true
+      use_more: false
+      use_more_always: true
+      use_more_text: more
+      header: {  }
+      footer: {  }
+      hide_attachment_summary: false
+      display_extenders: {  }
+    cache_metadata:
+      max-age: -1
+      contexts:
+        - 'languages:language_content'
+        - 'languages:language_interface'
+        - user.permissions
+      tags: {  }
+      cacheable: false
+  page_1:
+    id: page_1
+    display_title: Page
+    display_plugin: page
+    position: 1
+    display_options:
+      display_extenders: {  }
+      path: admin/moderate-comments
+    cache_metadata:
+      max-age: -1
+      contexts:
+        - 'languages:language_content'
+        - 'languages:language_interface'
+        - user.permissions
+      tags: {  }

core/modules/comment/tests/modules/comment_test_views/test_views/views.view.test_comment_user_uid.yml

@@ -0,0 +1,66 @@
+langcode: en
+status: true
+dependencies:
+  module:
+    - comment
+    - comment_test_views
+    - node
+    - user
+id: test_comment_user_uid
+label: test_comment_user_uid
+module: comment_test_views
+description: ''
+tag: default
+base_table: node_field_data
+base_field: nid
+display:
+  default:
+    display_options:
+      access:
+        type: perm
+      arguments:
+        uid_touch:
+          default_argument_type: fixed
+          field: uid_touch
+          id: uid_touch
+          summary:
+            format: default_summary
+            number_of_records: 0
+          summary_options:
+            items_per_page: 25
+          table: node_field_data
+          plugin_id: argument_comment_user_uid
+          entity_type: node
+      cache:
+        type: tag
+      exposed_form:
+        type: basic
+      fields:
+        nid:
+          field: nid
+          id: nid
+          table: node_field_data
+          plugin_id: node
+          entity_type: node
+          entity_field: nid
+        title:
+          field: title
+          id: title
+          table: node_field_data
+          plugin_id: field
+          entity_type: node
+          entity_field: title
+      pager:
+        type: full
+      query:
+        options:
+          query_comment: ''
+        type: views_query
+      style:
+        type: default
+      row:
+        type: 'entity:node'
+    display_plugin: default
+    display_title: Default
+    id: default
+    position: 0

core/modules/comment/tests/modules/comment_test_views/test_views/views.view.test_field_filters.yml

@@ -0,0 +1,324 @@
+langcode: en
+status: true
+dependencies:
+  module:
+    - comment
+    - node
+    - user
+id: test_field_filters
+label: 'Test field filters'
+module: views
+description: ''
+tag: ''
+base_table: comment_field_data
+base_field: cid
+display:
+  default:
+    display_plugin: default
+    id: default
+    display_title: Default
+    position: 0
+    display_options:
+      access:
+        type: perm
+        options:
+          perm: 'access content'
+      cache:
+        type: tag
+        options: {  }
+      query:
+        type: views_query
+        options:
+          disable_sql_rewrite: false
+          distinct: false
+          replica: false
+          query_comment: ''
+          query_tags: {  }
+      exposed_form:
+        type: basic
+        options:
+          submit_button: Apply
+          reset_button: false
+          reset_button_label: Reset
+          exposed_sorts_label: 'Sort by'
+          expose_sort_order: true
+          sort_asc_label: Asc
+          sort_desc_label: Desc
+      pager:
+        type: none
+        options:
+          items_per_page: 0
+          offset: 0
+      style:
+        type: default
+      row:
+        type: 'entity:comment'
+        options:
+          view_mode: default
+      relationships:
+        node:
+          id: node
+          table: comment_field_data
+          field: node
+          required: true
+          plugin_id: standard
+          relationship: none
+          group_type: group
+          admin_label: Content
+      fields:
+        subject:
+          id: subject
+          table: comment_field_data
+          field: subject
+          label: ''
+          alter:
+            alter_text: false
+            make_link: false
+            absolute: false
+            trim: false
+            word_boundary: false
+            ellipsis: false
+            strip_tags: false
+            html: false
+          hide_empty: false
+          empty_zero: false
+          relationship: none
+          group_type: group
+          admin_label: ''
+          exclude: false
+          element_type: ''
+          element_class: ''
+          element_label_type: ''
+          element_label_class: ''
+          element_label_colon: true
+          element_wrapper_type: ''
+          element_wrapper_class: ''
+          element_default_classes: true
+          empty: ''
+          hide_alter_empty: true
+          type: string
+          settings:
+            link_to_entity: false
+          plugin_id: field
+          entity_type: comment
+          entity_field: subject
+      filters:
+        subject:
+          id: subject
+          table: comment_field_data
+          field: subject
+          relationship: none
+          group_type: group
+          admin_label: ''
+          operator: contains
+          value: Comida
+          group: 1
+          exposed: false
+          expose:
+            operator_id: ''
+            label: ''
+            description: ''
+            use_operator: false
+            operator: ''
+            identifier: ''
+            required: false
+            remember: false
+            multiple: false
+            remember_roles:
+              authenticated: authenticated
+          is_grouped: false
+          group_info:
+            label: ''
+            description: ''
+            identifier: ''
+            optional: true
+            widget: select
+            multiple: false
+            remember: false
+            default_group: All
+            default_group_multiple: {  }
+            group_items: {  }
+          plugin_id: string
+          entity_type: comment
+          entity_field: subject
+      sorts: {  }
+      title: 'Title filter page'
+      header: {  }
+      footer: {  }
+      empty: {  }
+      arguments: {  }
+      rendering_language: '***LANGUAGE_entity_translation***'
+  page_bf:
+    display_plugin: page
+    id: page_bf
+    display_title: 'Body Comida'
+    position: 1
+    display_options:
+      path: test-body-filter
+      display_description: ''
+      filters:
+        comment_body_value:
+          id: comment_body_value
+          table: comment__comment_body
+          field: comment_body_value
+          relationship: none
+          group_type: group
+          admin_label: ''
+          operator: contains
+          value: Comida
+          group: 1
+          exposed: false
+          expose:
+            operator_id: ''
+            label: ''
+            description: ''
+            use_operator: false
+            operator: ''
+            identifier: ''
+            required: false
+            remember: false
+            multiple: false
+            remember_roles:
+              authenticated: authenticated
+          is_grouped: false
+          group_info:
+            label: ''
+            description: ''
+            identifier: ''
+            optional: true
+            widget: select
+            multiple: false
+            remember: false
+            default_group: All
+            default_group_multiple: {  }
+            group_items: {  }
+          plugin_id: string
+          entity_type: comment
+          entity_field: comment_body
+      defaults:
+        filters: false
+        filter_groups: false
+        title: false
+      filter_groups:
+        operator: AND
+        groups:
+          1: AND
+      title: 'Body filter page'
+  page_bp:
+    display_plugin: page
+    id: page_bp
+    display_title: 'Body Paris'
+    position: 1
+    display_options:
+      path: test-body-paris
+      display_description: ''
+      filters:
+        comment_body_value:
+          id: comment_body_value
+          table: comment__comment_body
+          field: comment_body_value
+          relationship: none
+          group_type: group
+          admin_label: ''
+          operator: contains
+          value: Paris
+          group: 1
+          exposed: false
+          expose:
+            operator_id: ''
+            label: ''
+            description: ''
+            use_operator: false
+            operator: ''
+            identifier: ''
+            required: false
+            remember: false
+            multiple: false
+            remember_roles:
+              authenticated: authenticated
+          is_grouped: false
+          group_info:
+            label: ''
+            description: ''
+            identifier: ''
+            optional: true
+            widget: select
+            multiple: false
+            remember: false
+            default_group: All
+            default_group_multiple: {  }
+            group_items: {  }
+          plugin_id: string
+          entity_type: comment
+          entity_field: comment_body
+      defaults:
+        filters: false
+        filter_groups: false
+        title: false
+      filter_groups:
+        operator: AND
+        groups:
+          1: AND
+      title: 'Body filter page'
+  page_tc:
+    display_plugin: page
+    id: page_tc
+    display_title: 'Title Comida'
+    position: 1
+    display_options:
+      path: test-title-filter
+      display_description: ''
+  page_tp:
+    display_plugin: page
+    id: page_tp
+    display_title: 'Title Paris'
+    position: 1
+    display_options:
+      path: test-title-paris
+      display_description: ''
+      filters:
+        subject:
+          id: subject
+          table: comment_field_data
+          field: subject
+          relationship: none
+          group_type: group
+          admin_label: ''
+          operator: contains
+          value: Paris
+          group: 1
+          exposed: false
+          expose:
+            operator_id: ''
+            label: ''
+            description: ''
+            use_operator: false
+            operator: ''
+            identifier: ''
+            required: false
+            remember: false
+            multiple: false
+            remember_roles:
+              authenticated: authenticated
+          is_grouped: false
+          group_info:
+            label: ''
+            description: ''
+            identifier: ''
+            optional: true
+            widget: select
+            multiple: false
+            remember: false
+            default_group: All
+            default_group_multiple: {  }
+            group_items: {  }
+          plugin_id: string
+          entity_type: comment
+          entity_field: subject
+      defaults:
+        filters: false
+        filter_groups: false
+      filter_groups:
+        operator: AND
+        groups:
+          1: AND

core/modules/comment/tests/modules/comment_test_views/test_views/views.view.test_new_comments.yml

@@ -0,0 +1,162 @@
+langcode: en
+status: true
+dependencies:
+  module:
+    - comment
+    - node
+    - user
+id: '2505879'
+label: '2505879'
+module: views
+description: ''
+tag: ''
+base_table: node_field_data
+base_field: nid
+display:
+  default:
+    display_plugin: default
+    id: default
+    display_title: Default
+    position: 0
+    display_options:
+      access:
+        type: perm
+        options:
+          perm: 'access content'
+      cache:
+        type: tag
+        options: {  }
+      query:
+        type: views_query
+        options:
+          disable_sql_rewrite: false
+          distinct: false
+          replica: false
+          query_comment: ''
+          query_tags: {  }
+      pager:
+        type: full
+      style:
+        type: table
+      row:
+        type: fields
+      fields:
+        title:
+          id: title
+          table: node_field_data
+          field: title
+          entity_type: node
+          entity_field: title
+          alter:
+            alter_text: false
+            make_link: false
+            absolute: false
+            trim: false
+            word_boundary: false
+            ellipsis: false
+            strip_tags: false
+            html: false
+          hide_empty: false
+          empty_zero: false
+          settings:
+            link_to_entity: true
+          plugin_id: field
+          relationship: none
+          group_type: group
+          admin_label: ''
+          label: Title
+          exclude: false
+          element_type: ''
+          element_class: ''
+          element_label_type: ''
+          element_label_class: ''
+          element_label_colon: true
+          element_wrapper_type: ''
+          element_wrapper_class: ''
+          element_default_classes: true
+          empty: ''
+          hide_alter_empty: true
+          click_sort_column: value
+          type: string
+          group_column: value
+          group_columns: {  }
+          group_rows: true
+          delta_limit: 0
+          delta_offset: 0
+          delta_reversed: false
+          delta_first_last: false
+          multi_type: separator
+          separator: ', '
+          field_api_classes: false
+        new_comments:
+          id: new_comments
+          table: node
+          field: new_comments
+          relationship: none
+          group_type: group
+          admin_label: ''
+          label: 'New comments'
+          exclude: false
+          alter:
+            alter_text: false
+            text: ''
+            make_link: false
+            path: ''
+            absolute: false
+            external: false
+            replace_spaces: false
+            path_case: none
+            trim_whitespace: false
+            alt: ''
+            rel: ''
+            link_class: ''
+            prefix: ''
+            suffix: ''
+            target: ''
+            nl2br: false
+            max_length: 0
+            word_boundary: true
+            ellipsis: true
+            more_link: false
+            more_link_text: ''
+            more_link_path: ''
+            strip_tags: false
+            trim: false
+            preserve_tags: ''
+            html: false
+          element_type: ''
+          element_class: ''
+          element_label_type: ''
+          element_label_class: ''
+          element_label_colon: true
+          element_wrapper_type: ''
+          element_wrapper_class: ''
+          element_default_classes: true
+          empty: ''
+          hide_empty: false
+          empty_zero: false
+          hide_alter_empty: true
+          set_precision: false
+          precision: 0
+          decimal: .
+          prefix: ''
+          suffix: ''
+          link_to_comment: true
+          entity_type: node
+          plugin_id: node_new_comments
+      filters: { }
+      sorts: { }
+      title: ''
+      header: {  }
+      footer: {  }
+      empty: {  }
+      relationships: {  }
+      arguments: {  }
+      display_extenders: {  }
+  page_1:
+    display_plugin: page
+    id: page_1
+    display_title: Page
+    position: 1
+    display_options:
+      path: 'test-new-comments'

core/modules/comment/tests/src/Functional/CommentAccessTest.php

@@ -0,0 +1,127 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+use Drupal\comment\Entity\Comment;
+use Drupal\comment\Tests\CommentTestTrait;
+use Drupal\node\Entity\NodeType;
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests comment administration and preview access.
+ *
+ * @group comment
+ */
+class CommentAccessTest extends BrowserTestBase {
+
+  use CommentTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'node',
+    'comment',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Node for commenting.
+   *
+   * @var \Drupal\node\NodeInterface
+   */
+  protected $unpublishedNode;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $node_type = NodeType::create([
+      'type' => 'article',
+      'name' => 'Article',
+    ]);
+    $node_type->save();
+    $node_author = $this->drupalCreateUser([
+      'create article content',
+      'access comments',
+    ]);
+
+    $this->drupalLogin($this->drupalCreateUser([
+      'edit own comments',
+      'skip comment approval',
+      'post comments',
+      'access comments',
+      'access content',
+    ]));
+
+    $this->addDefaultCommentField('node', 'article');
+    $this->unpublishedNode = $this->createNode([
+      'title' => 'This is unpublished',
+      'uid' => $node_author->id(),
+      'status' => 0,
+      'type' => 'article',
+    ]);
+    $this->unpublishedNode->save();
+  }
+
+  /**
+   * Tests commenting disabled for access-blocked entities.
+   */
+  public function testCannotCommentOnEntitiesYouCannotView(): void {
+    $assert = $this->assertSession();
+
+    $comment_url = 'comment/reply/node/' . $this->unpublishedNode->id() . '/comment';
+
+    // Commenting on an unpublished node results in access denied.
+    $this->drupalGet($comment_url);
+    $assert->statusCodeEquals(403);
+
+    // Publishing the node grants access.
+    $this->unpublishedNode->setPublished()->save();
+    $this->drupalGet($comment_url);
+    $assert->statusCodeEquals(200);
+  }
+
+  /**
+   * Tests cannot view comment reply form on entities you cannot view.
+   */
+  public function testCannotViewCommentReplyFormOnEntitiesYouCannotView(): void {
+    $assert = $this->assertSession();
+
+    // Create a comment on an unpublished node.
+    $comment = Comment::create([
+      'entity_type' => 'node',
+      'name' => 'Tony',
+      'hostname' => 'magic.example.com',
+      'mail' => 'foo@example.com',
+      'subject' => 'Comment on unpublished node',
+      'entity_id' => $this->unpublishedNode->id(),
+      'comment_type' => 'comment',
+      'field_name' => 'comment',
+      'pid' => 0,
+      'uid' => $this->unpublishedNode->getOwnerId(),
+      'status' => 1,
+    ]);
+    $comment->save();
+
+    $comment_url = 'comment/reply/node/' . $this->unpublishedNode->id() . '/comment/' . $comment->id();
+
+    // Replying to a comment on an unpublished node results in access denied.
+    $this->drupalGet($comment_url);
+    $assert->statusCodeEquals(403);
+
+    // Publishing the node grants access.
+    $this->unpublishedNode->setPublished()->save();
+    $this->drupalGet($comment_url);
+    $assert->statusCodeEquals(200);
+  }
+
+}

core/modules/comment/tests/src/Functional/CommentAdminTest.php

@@ -0,0 +1,293 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+use Drupal\comment\CommentInterface;
+use Drupal\Component\Render\FormattableMarkup;
+use Drupal\Component\Utility\Html;
+use Drupal\language\Entity\ConfigurableLanguage;
+use Drupal\user\RoleInterface;
+use Drupal\comment\Entity\Comment;
+
+/**
+ * Tests comment approval functionality.
+ *
+ * @group comment
+ */
+class CommentAdminTest extends CommentTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->drupalPlaceBlock('page_title_block');
+  }
+
+  /**
+   * Tests comment approval functionality through admin/content/comment.
+   */
+  public function testApprovalAdminInterface(): void {
+    // Set anonymous comments to require approval.
+    user_role_change_permissions(RoleInterface::ANONYMOUS_ID, [
+      'access comments' => TRUE,
+      'post comments' => TRUE,
+      'skip comment approval' => FALSE,
+    ]);
+    $this->drupalLogin($this->adminUser);
+    // Ensure that doesn't require contact info.
+    $this->setCommentAnonymous(CommentInterface::ANONYMOUS_MAYNOT_CONTACT);
+
+    // Test that the comments page loads correctly when there are no comments
+    $this->drupalGet('admin/content/comment');
+    $this->assertSession()->pageTextContains('No comments available.');
+
+    $this->drupalLogout();
+
+    // Post anonymous comment without contact info.
+    $subject = $this->randomMachineName();
+    $body = $this->randomMachineName();
+    // Set $contact to true so that it won't check for id and message.
+    $this->postComment($this->node, $body, $subject, TRUE);
+    $this->assertSession()->pageTextContains('Your comment has been queued for review by site administrators and will be published after approval.');
+
+    // Get unapproved comment id.
+    $this->drupalLogin($this->adminUser);
+    $anonymous_comment4 = $this->getUnapprovedComment($subject);
+    $anonymous_comment4 = Comment::create([
+      'cid' => $anonymous_comment4,
+      'subject' => $subject,
+      'comment_body' => $body,
+      'entity_id' => $this->node->id(),
+      'entity_type' => 'node',
+      'field_name' => 'comment',
+    ]);
+    $this->drupalLogout();
+
+    $this->assertFalse($this->commentExists($anonymous_comment4), 'Anonymous comment was not published.');
+
+    // Approve comment.
+    $this->drupalLogin($this->adminUser);
+    $this->performCommentOperation($anonymous_comment4, 'publish', TRUE);
+    $this->drupalLogout();
+
+    $this->drupalGet('node/' . $this->node->id());
+    $this->assertTrue($this->commentExists($anonymous_comment4), 'Anonymous comment visible.');
+
+    // Post 2 anonymous comments without contact info.
+    $comments[] = $this->postComment($this->node, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+    $comments[] = $this->postComment($this->node, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+
+    // Publish multiple comments in one operation.
+    $this->drupalLogin($this->adminUser);
+    $this->drupalGet('admin/content/comment/approval');
+    $this->assertSession()->pageTextContains('Unapproved comments (2)');
+    $edit = [
+      "comments[{$comments[0]->id()}]" => 1,
+      "comments[{$comments[1]->id()}]" => 1,
+    ];
+    $this->submitForm($edit, 'Update');
+    $this->assertSession()->pageTextContains('Unapproved comments (0)');
+
+    // Delete multiple comments in one operation.
+    $edit = [
+      'operation' => 'delete',
+      "comments[{$comments[0]->id()}]" => 1,
+      "comments[{$comments[1]->id()}]" => 1,
+      "comments[{$anonymous_comment4->id()}]" => 1,
+    ];
+    $this->submitForm($edit, 'Update');
+    $this->assertSession()->pageTextContains('Are you sure you want to delete these comments and all their children?');
+    $this->submitForm([], 'Delete');
+    $this->assertSession()->pageTextContains('No comments available.');
+    // Test message when no comments selected.
+    $edit = [
+      'operation' => 'delete',
+    ];
+    $this->submitForm($edit, 'Update');
+    $this->assertSession()->pageTextContains('Select one or more comments to perform the update on.');
+
+    // Make sure the label of unpublished node is not visible on listing page.
+    $this->drupalGet('admin/content/comment');
+    $this->postComment($this->node, $this->randomMachineName());
+    $this->drupalGet('admin/content/comment');
+    $this->assertSession()->pageTextContains(Html::escape($this->node->label()));
+    $this->node->setUnpublished()->save();
+    $this->drupalGet('admin/content/comment');
+    $this->assertSession()->pageTextNotContains(Html::escape($this->node->label()));
+  }
+
+  /**
+   * Tests comment approval functionality through the node interface.
+   */
+  public function testApprovalNodeInterface(): void {
+    // Set anonymous comments to require approval.
+    user_role_change_permissions(RoleInterface::ANONYMOUS_ID, [
+      'access comments' => TRUE,
+      'post comments' => TRUE,
+      'skip comment approval' => FALSE,
+    ]);
+    // Ensure that doesn't require contact info.
+    $this->setCommentAnonymous(CommentInterface::ANONYMOUS_MAYNOT_CONTACT);
+
+    // Post anonymous comment without contact info.
+    $subject = $this->randomMachineName();
+    $body = $this->randomMachineName();
+    // Set $contact to true so that it won't check for id and message.
+    $this->postComment($this->node, $body, $subject, TRUE);
+    $this->assertSession()->pageTextContains('Your comment has been queued for review by site administrators and will be published after approval.');
+
+    // Get unapproved comment id.
+    $this->drupalLogin($this->adminUser);
+    $anonymous_comment4 = $this->getUnapprovedComment($subject);
+    $anonymous_comment4 = Comment::create([
+      'cid' => $anonymous_comment4,
+      'subject' => $subject,
+      'comment_body' => $body,
+      'entity_id' => $this->node->id(),
+      'entity_type' => 'node',
+      'field_name' => 'comment',
+    ]);
+    $this->drupalLogout();
+
+    $this->assertFalse($this->commentExists($anonymous_comment4), 'Anonymous comment was not published.');
+
+    // Ensure comments cannot be approved without a valid token.
+    $this->drupalLogin($this->adminUser);
+    $this->drupalGet('comment/1/approve');
+    $this->assertSession()->statusCodeEquals(403);
+    $this->drupalGet('comment/1/approve', ['query' => ['token' => 'forged']]);
+    $this->assertSession()->statusCodeEquals(403);
+
+    // Approve comment.
+    $this->drupalGet('comment/1/edit');
+    $this->assertSession()->checkboxChecked('edit-status-0');
+    $this->drupalGet('node/' . $this->node->id());
+    $this->clickLink('Approve');
+    $this->drupalLogout();
+
+    $this->drupalGet('node/' . $this->node->id());
+    $this->assertTrue($this->commentExists($anonymous_comment4), 'Anonymous comment visible.');
+  }
+
+  /**
+   * Tests comment bundle admin.
+   */
+  public function testCommentAdmin(): void {
+    // Login.
+    $this->drupalLogin($this->adminUser);
+    // Browse to comment bundle overview.
+    $this->drupalGet('admin/structure/comment');
+    $this->assertSession()->statusCodeEquals(200);
+    // Make sure titles visible.
+    $this->assertSession()->pageTextContains('Comment type');
+    $this->assertSession()->pageTextContains('Description');
+    // Make sure the description is present.
+    $this->assertSession()->pageTextContains('Default comment field');
+    // Manage fields.
+    $this->clickLink('Manage fields');
+    $this->assertSession()->statusCodeEquals(200);
+    // Make sure comment_body field is shown.
+    $this->assertSession()->pageTextContains('comment_body');
+    // Rest from here on in is field_ui.
+  }
+
+  /**
+   * Tests editing a comment as an admin.
+   */
+  public function testEditComment(): void {
+    // Enable anonymous user comments.
+    user_role_grant_permissions(RoleInterface::ANONYMOUS_ID, [
+      'access comments',
+      'post comments',
+      'skip comment approval',
+    ]);
+
+    // Log in as a web user.
+    $this->drupalLogin($this->webUser);
+    // Post a comment.
+    $comment = $this->postComment($this->node, $this->randomMachineName());
+
+    $this->drupalLogout();
+
+    // Post anonymous comment.
+    // Ensure that we need email id before posting comment.
+    $this->setCommentAnonymous(CommentInterface::ANONYMOUS_MUST_CONTACT);
+
+    // Post comment with contact info (required).
+    $author_name = $this->randomMachineName();
+    $author_mail = $this->randomMachineName() . '@example.com';
+    $anonymous_comment = $this->postComment($this->node, $this->randomMachineName(), $this->randomMachineName(), ['name' => $author_name, 'mail' => $author_mail]);
+
+    // Log in as an admin user.
+    $this->drupalLogin($this->adminUser);
+
+    // Make sure the comment field is not visible when
+    // the comment was posted by an authenticated user.
+    $this->drupalGet('comment/' . $comment->id() . '/edit');
+    $this->assertSession()->fieldNotExists('edit-mail');
+
+    // Make sure the comment field is visible when
+    // the comment was posted by an anonymous user.
+    $this->drupalGet('comment/' . $anonymous_comment->id() . '/edit');
+    $this->assertSession()->fieldValueEquals('edit-mail', $anonymous_comment->getAuthorEmail());
+  }
+
+  /**
+   * Tests commented translation deletion admin view.
+   */
+  public function testCommentedTranslationDeletion(): void {
+    \Drupal::service('module_installer')->install([
+      'language',
+      'locale',
+    ]);
+    \Drupal::service('router.builder')->rebuildIfNeeded();
+
+    ConfigurableLanguage::createFromLangcode('ur')->save();
+    // Rebuild the container to update the default language container variable.
+    $this->rebuildContainer();
+    // Ensure that doesn't require contact info.
+    $this->setCommentAnonymous(CommentInterface::ANONYMOUS_MAYNOT_CONTACT);
+    $this->drupalLogin($this->webUser);
+    $count_query = \Drupal::entityTypeManager()
+      ->getStorage('comment')
+      ->getQuery()
+      ->accessCheck(FALSE)
+      ->count();
+    $before_count = $count_query->execute();
+    // Post 2 anonymous comments without contact info.
+    $comment1 = $this->postComment($this->node, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+    $comment2 = $this->postComment($this->node, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+
+    $comment1->addTranslation('ur', ['subject' => 'ur ' . $comment1->label()])
+      ->save();
+    $comment2->addTranslation('ur', ['subject' => 'ur ' . $comment1->label()])
+      ->save();
+    $this->drupalLogout();
+    $this->drupalLogin($this->adminUser);
+    // Delete multiple comments in one operation.
+    $edit = [
+      'operation' => 'delete',
+      "comments[{$comment1->id()}]" => 1,
+      "comments[{$comment2->id()}]" => 1,
+    ];
+    $this->drupalGet('admin/content/comment');
+    $this->submitForm($edit, 'Update');
+    $this->assertSession()->responseContains(new FormattableMarkup('@label (Original translation) - <em>The following comment translations will be deleted:</em>', ['@label' => $comment1->label()]));
+    $this->assertSession()->responseContains(new FormattableMarkup('@label (Original translation) - <em>The following comment translations will be deleted:</em>', ['@label' => $comment2->label()]));
+    $this->assertSession()->pageTextContains('English');
+    $this->assertSession()->pageTextContains('Urdu');
+    $this->submitForm([], 'Delete');
+    $after_count = $count_query->execute();
+    $this->assertEquals($before_count, $after_count, 'No comment or translation found.');
+  }
+
+}

core/modules/comment/tests/src/Functional/CommentAnonymousTest.php

@@ -0,0 +1,214 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+use Drupal\comment\CommentInterface;
+use Drupal\user\RoleInterface;
+
+/**
+ * Tests anonymous commenting.
+ *
+ * @group comment
+ */
+class CommentAnonymousTest extends CommentTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // Enable anonymous and authenticated user comments.
+    user_role_grant_permissions(RoleInterface::ANONYMOUS_ID, [
+      'access comments',
+      'post comments',
+      'skip comment approval',
+    ]);
+    user_role_grant_permissions(RoleInterface::AUTHENTICATED_ID, [
+      'access comments',
+      'post comments',
+      'skip comment approval',
+    ]);
+  }
+
+  /**
+   * Tests anonymous comment functionality.
+   */
+  public function testAnonymous(): void {
+    $this->setCommentAnonymous(CommentInterface::ANONYMOUS_MAYNOT_CONTACT);
+
+    // Preview comments (with `skip comment approval` permission).
+    $edit = [];
+    $title = 'comment title with skip comment approval';
+    $body = 'comment body with skip comment approval';
+    $edit['subject[0][value]'] = $title;
+    $edit['comment_body[0][value]'] = $body;
+    $this->drupalGet($this->node->toUrl());
+    $this->submitForm($edit, 'Preview');
+    // Cannot use assertRaw here since both title and body are in the form.
+    $preview = (string) $this->cssSelect('[data-drupal-selector="edit-comment-preview"]')[0]->getHtml();
+    $this->assertStringContainsString($title, $preview, 'Anonymous user can preview comment title.');
+    $this->assertStringContainsString($body, $preview, 'Anonymous user can preview comment body.');
+
+    // Preview comments (without `skip comment approval` permission).
+    user_role_revoke_permissions(RoleInterface::ANONYMOUS_ID, ['skip comment approval']);
+    $edit = [];
+    $title = 'comment title without skip comment approval';
+    $body = 'comment body without skip comment approval';
+    $edit['subject[0][value]'] = $title;
+    $edit['comment_body[0][value]'] = $body;
+    $this->drupalGet($this->node->toUrl());
+    $this->submitForm($edit, 'Preview');
+    // Cannot use assertRaw here since both title and body are in the form.
+    $preview = (string) $this->cssSelect('[data-drupal-selector="edit-comment-preview"]')[0]->getHtml();
+    $this->assertStringContainsString($title, $preview, 'Anonymous user can preview comment title.');
+    $this->assertStringContainsString($body, $preview, 'Anonymous user can preview comment body.');
+    user_role_grant_permissions(RoleInterface::ANONYMOUS_ID, ['skip comment approval']);
+
+    // Post anonymous comment without contact info.
+    $anonymous_comment1 = $this->postComment($this->node, $this->randomMachineName(), $this->randomMachineName());
+    $this->assertTrue($this->commentExists($anonymous_comment1), 'Anonymous comment without contact info found.');
+
+    // Ensure anonymous users cannot post in the name of registered users.
+    $edit = [
+      'name' => $this->adminUser->getAccountName(),
+      'comment_body[0][value]' => $this->randomMachineName(),
+    ];
+    $this->drupalGet('comment/reply/node/' . $this->node->id() . '/comment');
+    $this->submitForm($edit, 'Save');
+    $this->assertSession()->pageTextContains('The name you used (' . $this->adminUser->getAccountName() . ') belongs to a registered user.');
+
+    // Allow contact info.
+    $this->drupalLogin($this->adminUser);
+    $this->setCommentAnonymous(CommentInterface::ANONYMOUS_MAY_CONTACT);
+
+    // Attempt to edit anonymous comment.
+    $this->drupalGet('comment/' . $anonymous_comment1->id() . '/edit');
+    $edited_comment = $this->postComment(NULL, $this->randomMachineName(), $this->randomMachineName());
+    $this->assertTrue($this->commentExists($edited_comment, FALSE), 'Modified reply found.');
+    $this->drupalLogout();
+
+    // Post anonymous comment with contact info (optional).
+    $this->drupalGet('comment/reply/node/' . $this->node->id() . '/comment');
+    $this->assertTrue($this->commentContactInfoAvailable(), 'Contact information available.');
+
+    // Check the presence of expected cache tags.
+    $this->assertSession()->responseHeaderContains('X-Drupal-Cache-Tags', 'config:field.field.node.article.comment');
+    $this->assertSession()->responseHeaderContains('X-Drupal-Cache-Tags', 'config:user.settings');
+
+    $anonymous_comment2 = $this->postComment($this->node, $this->randomMachineName(), $this->randomMachineName());
+    $this->assertTrue($this->commentExists($anonymous_comment2), 'Anonymous comment with contact info (optional) found.');
+
+    // Ensure anonymous users cannot post in the name of registered users.
+    $edit = [
+      'name' => $this->adminUser->getAccountName(),
+      'mail' => $this->randomMachineName() . '@example.com',
+      'subject[0][value]' => $this->randomMachineName(),
+      'comment_body[0][value]' => $this->randomMachineName(),
+    ];
+    $this->drupalGet('comment/reply/node/' . $this->node->id() . '/comment');
+    $this->submitForm($edit, 'Save');
+    $this->assertSession()->pageTextContains('The name you used (' . $this->adminUser->getAccountName() . ') belongs to a registered user.');
+
+    // Require contact info.
+    $this->setCommentAnonymous(CommentInterface::ANONYMOUS_MUST_CONTACT);
+
+    // Try to post comment with contact info (required).
+    $this->drupalGet('comment/reply/node/' . $this->node->id() . '/comment');
+    $this->assertTrue($this->commentContactInfoAvailable(), 'Contact information available.');
+
+    $anonymous_comment3 = $this->postComment($this->node, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+    // Name should have 'Anonymous' for value by default.
+    $this->assertSession()->pageTextContains('Email field is required.');
+    $this->assertFalse($this->commentExists($anonymous_comment3), 'Anonymous comment with contact info (required) not found.');
+
+    // Post comment with contact info (required).
+    $author_name = $this->randomMachineName();
+    $author_mail = $this->randomMachineName() . '@example.com';
+    $anonymous_comment3 = $this->postComment($this->node, $this->randomMachineName(), $this->randomMachineName(), ['name' => $author_name, 'mail' => $author_mail]);
+    $this->assertTrue($this->commentExists($anonymous_comment3), 'Anonymous comment with contact info (required) found.');
+
+    // Make sure the user data appears correctly when editing the comment.
+    $this->drupalLogin($this->adminUser);
+    $this->drupalGet('comment/' . $anonymous_comment3->id() . '/edit');
+    $this->assertSession()->responseContains($author_name);
+    // Check the author field is empty (i.e. anonymous) when editing the comment.
+    $this->assertSession()->fieldValueEquals('uid', '');
+    $this->assertSession()->responseContains($author_mail);
+
+    // Unpublish comment.
+    $this->performCommentOperation($anonymous_comment3, 'unpublish');
+
+    $this->drupalGet('admin/content/comment/approval');
+    $this->assertSession()->responseContains('comments[' . $anonymous_comment3->id() . ']');
+
+    // Publish comment.
+    $this->performCommentOperation($anonymous_comment3, 'publish', TRUE);
+
+    $this->drupalGet('admin/content/comment');
+    $this->assertSession()->responseContains('comments[' . $anonymous_comment3->id() . ']');
+
+    // Delete comment.
+    $this->performCommentOperation($anonymous_comment3, 'delete');
+
+    $this->drupalGet('admin/content/comment');
+    $this->assertSession()->responseNotContains('comments[' . $anonymous_comment3->id() . ']');
+    $this->drupalLogout();
+
+    // Comment 3 was deleted.
+    $this->drupalGet('comment/reply/node/' . $this->node->id() . '/comment/' . $anonymous_comment3->id());
+    $this->assertSession()->statusCodeEquals(403);
+
+    // Reset.
+    user_role_change_permissions(RoleInterface::ANONYMOUS_ID, [
+      'access comments' => FALSE,
+      'post comments' => FALSE,
+      'skip comment approval' => FALSE,
+    ]);
+
+    // Attempt to view comments while disallowed.
+    // NOTE: if authenticated user has permission to post comments, then a
+    // "Login or register to post comments" type link may be shown.
+    $this->drupalGet('node/' . $this->node->id());
+    // Verify that comments were not displayed.
+    $this->assertSession()->responseNotMatches('@<h2[^>]*>Comments</h2>@');
+    $this->assertSession()->linkNotExists('Add new comment', 'Link to add comment was found.');
+
+    // Attempt to view node-comment form while disallowed.
+    $this->drupalGet('comment/reply/node/' . $this->node->id() . '/comment');
+    $this->assertSession()->statusCodeEquals(403);
+
+    user_role_change_permissions(RoleInterface::ANONYMOUS_ID, [
+      'access comments' => TRUE,
+      'post comments' => FALSE,
+      'skip comment approval' => FALSE,
+    ]);
+    $this->drupalGet('node/' . $this->node->id());
+    // Verify that the comment field title is displayed.
+    $this->assertSession()->responseMatches('@<h2[^>]*>Comments</h2>@');
+    $this->assertSession()->linkExists('Log in', 1, 'Link to login was found.');
+    $this->assertSession()->linkExists('register', 1, 'Link to register was found.');
+
+    user_role_change_permissions(RoleInterface::ANONYMOUS_ID, [
+      'access comments' => FALSE,
+      'post comments' => TRUE,
+      'skip comment approval' => TRUE,
+    ]);
+    $this->drupalGet('node/' . $this->node->id());
+    // Verify that comments were not displayed.
+    $this->assertSession()->responseNotMatches('@<h2[^>]*>Comments</h2>@');
+    $this->assertSession()->fieldValueEquals('subject[0][value]', '');
+    $this->assertSession()->fieldValueEquals('comment_body[0][value]', '');
+
+    $this->drupalGet('comment/reply/node/' . $this->node->id() . '/comment/' . $anonymous_comment2->id());
+    $this->assertSession()->statusCodeEquals(403);
+  }
+
+}

core/modules/comment/tests/src/Functional/CommentBlockTest.php

@@ -0,0 +1,99 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+use Drupal\user\RoleInterface;
+
+/**
+ * Tests comment block functionality.
+ *
+ * @group comment
+ */
+class CommentBlockTest extends CommentTestBase {
+
+  /**
+   * Modules to install.
+   *
+   * @var array
+   */
+  protected static $modules = ['block', 'views'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    // Update admin user to have the 'administer blocks' permission.
+    $this->adminUser = $this->drupalCreateUser([
+      'administer content types',
+      'administer comments',
+      'skip comment approval',
+      'post comments',
+      'access comments',
+      'access content',
+      'administer blocks',
+    ]);
+  }
+
+  /**
+   * Tests the recent comments block.
+   */
+  public function testRecentCommentBlock(): void {
+    $this->drupalLogin($this->adminUser);
+    $this->drupalPlaceBlock('views_block:comments_recent-block_1');
+
+    // Add some test comments, with and without subjects. Because the 10 newest
+    // comments should be shown by the block, we create 11 to test that behavior
+    // below.
+    $timestamp = \Drupal::time()->getRequestTime();
+    for ($i = 0; $i < 11; ++$i) {
+      $subject = ($i % 2) ? $this->randomMachineName() : '';
+      $comments[$i] = $this->postComment($this->node, $this->randomMachineName(), $subject);
+      $comments[$i]->created->value = $timestamp--;
+      $comments[$i]->save();
+    }
+
+    // Test that a user without the 'access comments' permission cannot see the
+    // block.
+    $this->drupalLogout();
+    user_role_revoke_permissions(RoleInterface::ANONYMOUS_ID, ['access comments']);
+    $this->drupalGet('');
+    $this->assertSession()->pageTextNotContains('Recent comments');
+    user_role_grant_permissions(RoleInterface::ANONYMOUS_ID, ['access comments']);
+
+    // Test that a user with the 'access comments' permission can see the
+    // block.
+    $this->drupalLogin($this->webUser);
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains('Recent comments');
+
+    // Test the only the 10 latest comments are shown and in the proper order.
+    $this->assertSession()->pageTextNotContains($comments[10]->getSubject());
+    for ($i = 0; $i < 10; $i++) {
+      $this->assertSession()->pageTextContains($comments[$i]->getSubject());
+      if ($i > 1) {
+        $previous_position = $position;
+        $position = strpos($this->getSession()->getPage()->getContent(), $comments[$i]->getSubject());
+        $this->assertGreaterThan($previous_position, $position, sprintf('Comment %d does not appear after comment %d', 10 - $i, 11 - $i));
+      }
+      $position = strpos($this->getSession()->getPage()->getContent(), $comments[$i]->getSubject());
+    }
+
+    // Test that links to comments work when comments are across pages.
+    $this->setCommentsPerPage(1);
+
+    for ($i = 0; $i < 10; $i++) {
+      $this->clickLink($comments[$i]->getSubject());
+      $this->assertSession()->pageTextContains($comments[$i]->getSubject());
+      $this->assertSession()->responseContains('<link rel="canonical"');
+    }
+  }
+
+}

core/modules/comment/tests/src/Functional/CommentCSSTest.php

@@ -0,0 +1,149 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+use Drupal\Core\Language\LanguageInterface;
+use Drupal\comment\CommentInterface;
+use Drupal\user\RoleInterface;
+use Drupal\comment\Entity\Comment;
+use Drupal\Tests\Traits\Core\GeneratePermutationsTrait;
+
+/**
+ * Tests CSS classes on comments.
+ *
+ * @group comment
+ */
+class CommentCSSTest extends CommentTestBase {
+
+  use GeneratePermutationsTrait;
+
+  /**
+   * The theme to install as the default for testing.
+   *
+   * @var string
+   */
+  protected $defaultTheme = 'starterkit_theme';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // Allow anonymous users to see comments.
+    user_role_grant_permissions(RoleInterface::ANONYMOUS_ID, [
+      'access comments',
+      'access content',
+    ]);
+  }
+
+  /**
+   * Tests CSS classes on comments.
+   */
+  public function testCommentClasses(): void {
+    // Create all permutations for comments, users, and nodes.
+    $parameters = [
+      'node_uid' => [0, $this->webUser->id()],
+      'comment_uid' => [0, $this->webUser->id(), $this->adminUser->id()],
+      'comment_status' => [CommentInterface::PUBLISHED, CommentInterface::NOT_PUBLISHED],
+      'user' => ['anonymous', 'authenticated', 'admin'],
+    ];
+    $permutations = $this->generatePermutations($parameters);
+
+    foreach ($permutations as $case) {
+      // Create a new node.
+      $node = $this->drupalCreateNode(['type' => 'article', 'uid' => $case['node_uid']]);
+
+      // Add a comment.
+      /** @var \Drupal\comment\CommentInterface $comment */
+      $comment = Comment::create([
+        'entity_id' => $node->id(),
+        'entity_type' => 'node',
+        'field_name' => 'comment',
+        'uid' => $case['comment_uid'],
+        'status' => $case['comment_status'],
+        'subject' => $this->randomMachineName(),
+        'language' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
+        'comment_body' => [LanguageInterface::LANGCODE_NOT_SPECIFIED => [$this->randomMachineName()]],
+      ]);
+      $comment->save();
+
+      // Adjust the current/viewing user.
+      switch ($case['user']) {
+        case 'anonymous':
+          if ($this->loggedInUser) {
+            $this->drupalLogout();
+          }
+          $case['user_uid'] = 0;
+          break;
+
+        case 'authenticated':
+          $this->drupalLogin($this->webUser);
+          $case['user_uid'] = $this->webUser->id();
+          break;
+
+        case 'admin':
+          $this->drupalLogin($this->adminUser);
+          $case['user_uid'] = $this->adminUser->id();
+          break;
+      }
+      // Request the node with the comment.
+      $this->drupalGet('node/' . $node->id());
+      $settings = $this->getDrupalSettings();
+
+      // Verify the data-history-node-id attribute, which is necessary for the
+      // by-viewer class and the "new" indicator, see below.
+      $this->assertSession()->elementsCount('xpath', '//*[@data-history-node-id="' . $node->id() . '"]', 1);
+
+      // Verify classes if the comment is visible for the current user.
+      if ($case['comment_status'] == CommentInterface::PUBLISHED || $case['user'] == 'admin') {
+        // Verify the by-anonymous class.
+        $comments = '//*[contains(@class, "comment") and contains(@class, "by-anonymous")]';
+        if ($case['comment_uid'] == 0) {
+          $this->assertSession()->elementsCount('xpath', $comments, 1);
+        }
+        else {
+          $this->assertSession()->elementNotExists('xpath', $comments);
+        }
+
+        // Verify the by-node-author class.
+        $comments = '//*[contains(@class, "comment") and contains(@class, "by-node-author")]';
+        if ($case['comment_uid'] > 0 && $case['comment_uid'] == $case['node_uid']) {
+          $this->assertSession()->elementsCount('xpath', $comments, 1);
+        }
+        else {
+          $this->assertSession()->elementNotExists('xpath', $comments);
+        }
+
+        // Verify the data-comment-user-id attribute, which is used by the
+        // drupal.comment-by-viewer library to add a by-viewer when the current
+        // user (the viewer) was the author of the comment. We do this in Java-
+        // Script to prevent breaking the render cache.
+        $this->assertSession()->elementsCount('xpath', '//*[contains(@class, "comment") and @data-comment-user-id="' . $case['comment_uid'] . '"]', 1);
+        $this->assertSession()->responseContains($this->getModulePath('comment') . '/js/comment-by-viewer.js');
+      }
+
+      // Verify the unpublished class.
+      $comments = '//*[contains(@class, "comment") and contains(@class, "unpublished")]';
+      if ($case['comment_status'] == CommentInterface::NOT_PUBLISHED && $case['user'] == 'admin') {
+        $this->assertSession()->elementsCount('xpath', $comments, 1);
+      }
+      else {
+        $this->assertSession()->elementNotExists('xpath', $comments);
+      }
+
+      // Verify the data-comment-timestamp attribute, which is used by the
+      // drupal.comment-new-indicator library to add a "new" indicator to each
+      // comment that was created or changed after the last time the current
+      // user read the corresponding node.
+      if ($case['comment_status'] == CommentInterface::PUBLISHED || $case['user'] == 'admin') {
+        $this->assertSession()->elementsCount('xpath', '//*[contains(@class, "comment")]/*[@data-comment-timestamp="' . $comment->getChangedTime() . '"]', 1);
+        $expectedJS = ($case['user'] !== 'anonymous');
+        $this->assertSame($expectedJS, isset($settings['ajaxPageState']['libraries']) && in_array('comment/drupal.comment-new-indicator', explode(',', $settings['ajaxPageState']['libraries'])), 'drupal.comment-new-indicator library is present.');
+      }
+    }
+  }
+
+}

core/modules/comment/tests/src/Functional/CommentCacheTagsTest.php

@@ -0,0 +1,177 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+use Drupal\comment\CommentInterface;
+use Drupal\comment\CommentManagerInterface;
+use Drupal\comment\Entity\Comment;
+use Drupal\comment\Tests\CommentTestTrait;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Language\LanguageInterface;
+use Drupal\entity_test\Entity\EntityTest;
+use Drupal\field\Entity\FieldConfig;
+use Drupal\Tests\system\Functional\Entity\EntityWithUriCacheTagsTestBase;
+use Drupal\user\Entity\Role;
+use Drupal\user\RoleInterface;
+
+// cspell:ignore amphibius Hippopotamidae
+
+/**
+ * Tests the Comment entity's cache tags.
+ *
+ * @group comment
+ */
+class CommentCacheTagsTest extends EntityWithUriCacheTagsTestBase {
+
+  use CommentTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['comment'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * @var \Drupal\entity_test\Entity\EntityTest
+   */
+  protected $entityTestCamelid;
+
+  /**
+   * @var \Drupal\entity_test\Entity\EntityTest
+   */
+  protected $entityTestHippopotamidae;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // Give anonymous users permission to view comments, so that we can verify
+    // the cache tags of cached versions of comment pages.
+    $user_role = Role::load(RoleInterface::ANONYMOUS_ID);
+    $user_role->grantPermission('access comments');
+    $user_role->save();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function createEntity() {
+    // Create a "bar" bundle for the "entity_test" entity type and create.
+    $bundle = 'bar';
+    entity_test_create_bundle($bundle, NULL, 'entity_test');
+
+    // Create a comment field on this bundle.
+    $this->addDefaultCommentField('entity_test', 'bar', 'comment');
+
+    // Display comments in a flat list; threaded comments are not render cached.
+    $field = FieldConfig::loadByName('entity_test', 'bar', 'comment');
+    $field->setSetting('default_mode', CommentManagerInterface::COMMENT_MODE_FLAT);
+    $field->save();
+
+    // Create a "Camelids" test entity that the comment will be assigned to.
+    $this->entityTestCamelid = EntityTest::create([
+      'name' => 'Camelids',
+      'type' => 'bar',
+    ]);
+    $this->entityTestCamelid->save();
+
+    // Create a "Llama" comment.
+    $comment = Comment::create([
+      'subject' => 'Llama',
+      'comment_body' => [
+        'value' => 'The name "llama" was adopted by European settlers from native Peruvians.',
+        'format' => 'plain_text',
+      ],
+      'entity_id' => $this->entityTestCamelid->id(),
+      'entity_type' => 'entity_test',
+      'field_name' => 'comment',
+      'status' => CommentInterface::PUBLISHED,
+    ]);
+    $comment->save();
+
+    return $comment;
+  }
+
+  /**
+   * Tests that comments invalidate the cache tag of their host entity.
+   */
+  public function testCommentEntity(): void {
+    $this->verifyPageCache($this->entityTestCamelid->toUrl(), 'MISS');
+    $this->verifyPageCache($this->entityTestCamelid->toUrl(), 'HIT');
+
+    // Create a "Hippopotamus" comment.
+    $this->entityTestHippopotamidae = EntityTest::create([
+      'name' => 'Hippopotamus',
+      'type' => 'bar',
+    ]);
+    $this->entityTestHippopotamidae->save();
+
+    $this->verifyPageCache($this->entityTestHippopotamidae->toUrl(), 'MISS');
+    $this->verifyPageCache($this->entityTestHippopotamidae->toUrl(), 'HIT');
+
+    $hippo_comment = Comment::create([
+      'subject' => 'Hippopotamus',
+      'comment_body' => [
+        'value' => 'The common hippopotamus (Hippopotamus amphibius), or hippo, is a large, mostly herbivorous mammal in sub-Saharan Africa',
+        'format' => 'plain_text',
+      ],
+      'entity_id' => $this->entityTestHippopotamidae->id(),
+      'entity_type' => 'entity_test',
+      'field_name' => 'comment',
+      'status' => CommentInterface::PUBLISHED,
+    ]);
+    $hippo_comment->save();
+
+    // Ensure that a new comment only invalidates the commented entity.
+    $this->verifyPageCache($this->entityTestCamelid->toUrl(), 'HIT');
+    $this->verifyPageCache($this->entityTestHippopotamidae->toUrl(), 'MISS');
+    $this->assertSession()->pageTextContains($hippo_comment->getSubject());
+
+    // Ensure that updating an existing comment only invalidates the commented
+    // entity.
+    $this->entity->save();
+    $this->verifyPageCache($this->entityTestCamelid->toUrl(), 'MISS');
+    $this->verifyPageCache($this->entityTestHippopotamidae->toUrl(), 'HIT');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getAdditionalCacheContextsForEntity(EntityInterface $entity) {
+    return [];
+  }
+
+  /**
+   * {@inheritdoc}
+   *
+   * Each comment must have a comment body, which always has a text format.
+   */
+  protected function getAdditionalCacheTagsForEntity(EntityInterface $entity) {
+    /** @var \Drupal\comment\CommentInterface $entity */
+    return [
+      'config:filter.format.plain_text',
+      'user:' . $entity->getOwnerId(),
+      'user_view',
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getDefaultCacheContexts() {
+    return [
+      'languages:' . LanguageInterface::TYPE_INTERFACE,
+      'theme',
+      'user.permissions',
+    ];
+  }
+
+}

core/modules/comment/tests/src/Functional/CommentDisplayConfigurableTest.php

@@ -0,0 +1,87 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+use Drupal\Core\Entity\Entity\EntityViewDisplay;
+use Drupal\Core\Language\LanguageInterface;
+use Drupal\comment\CommentInterface;
+use Drupal\comment\Entity\Comment;
+use Drupal\user\RoleInterface;
+
+/**
+ * Tests making comment base fields' displays configurable.
+ *
+ * @group comment
+ */
+class CommentDisplayConfigurableTest extends CommentTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'olivero';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // Allow anonymous users to see comments.
+    user_role_grant_permissions(RoleInterface::ANONYMOUS_ID, [
+      'access comments',
+      'access content',
+    ]);
+  }
+
+  /**
+   * Sets base fields to configurable display and check settings are respected.
+   */
+  public function testDisplayConfigurable(): void {
+    // Add a comment.
+    $nid = $this->node->id();
+    /** @var \Drupal\comment\CommentInterface $comment */
+    $comment = Comment::create([
+      'entity_id' => $nid,
+      'entity_type' => 'node',
+      'field_name' => 'comment',
+      'uid' => $this->webUser->id(),
+      'status' => CommentInterface::PUBLISHED,
+      'subject' => $this->randomMachineName(),
+      'language' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
+      'comment_body' => [LanguageInterface::LANGCODE_NOT_SPECIFIED => [$this->randomMachineName()]],
+    ]);
+    $comment->save();
+    $assert = $this->assertSession();
+
+    // Check the comment author with Drupal default non-configurable display.
+    $this->drupalGet('node/' . $nid);
+    $assert->elementExists('css', 'p.comment__author span');
+
+    // Enable module to make base fields' displays configurable.
+    \Drupal::service('module_installer')->install(['comment_display_configurable_test']);
+
+    // Configure display.
+    $display = EntityViewDisplay::load('comment.comment.default');
+    $display->setComponent('uid',
+      [
+        'type' => 'entity_reference_label',
+        'label' => 'above',
+        'settings' => ['link' => FALSE],
+      ])
+      ->save();
+    // Recheck the comment author with configurable display.
+    $this->drupalGet('node/' . $nid);
+    $assert->elementExists('css', '.field--name-uid .field__item');
+
+    // Remove from display.
+    $display->removeComponent('uid')
+      ->removeComponent('created')
+      ->save();
+
+    $this->drupalGet('node/' . $this->node->id());
+    $assert->elementNotExists('css', '.field--name-uid .field__item');
+  }
+
+}

core/modules/comment/tests/src/Functional/CommentEntityReferenceTest.php

@@ -0,0 +1,126 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+use Drupal\comment\Entity\Comment;
+use Drupal\Tests\field\Traits\EntityReferenceFieldCreationTrait;
+
+/**
+ * Tests that comments behave correctly when added as entity references.
+ *
+ * @group comment
+ */
+class CommentEntityReferenceTest extends CommentTestBase {
+
+  use EntityReferenceFieldCreationTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * A second test node containing references to comments.
+   *
+   * @var \Drupal\node\NodeInterface
+   */
+  protected $node2;
+
+  /**
+   * A comment linked to a node.
+   *
+   * @var \Drupal\comment\CommentInterface
+   */
+  protected $comment;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->createEntityReferenceField(
+      'node',
+      'article',
+      'entity_reference_comment',
+      'Entity Reference Comment',
+      'comment',
+      'default',
+      ['target_bundles' => ['comment']]
+    );
+    \Drupal::service('entity_display.repository')
+      ->getFormDisplay('node', 'article')
+      ->setComponent('entity_reference_comment', ['type' => 'options_select'])
+      ->save();
+    \Drupal::service('entity_display.repository')
+      ->getViewDisplay('node', 'article')
+      ->setComponent('entity_reference_comment', ['type' => 'entity_reference_label'])
+      ->save();
+
+    $administratorUser = $this->drupalCreateUser([
+      'skip comment approval',
+      'post comments',
+      'access comments',
+      'access content',
+      'administer nodes',
+      'administer comments',
+      'bypass node access',
+    ]);
+    $this->drupalLogin($administratorUser);
+
+    $this->node = $this->drupalCreateNode(['type' => 'article', 'promote' => 1, 'uid' => $this->webUser->id()]);
+    $this->comment = $this->postComment($this->node, $this->randomMachineName(), $this->randomMachineName());
+    $this->assertInstanceOf(Comment::class, $this->comment);
+
+    $this->node2 = $this->drupalCreateNode([
+      'title' => $this->randomMachineName(),
+      'type' => 'article',
+    ]);
+  }
+
+  /**
+   * Tests that comments are correctly saved as entity references.
+   */
+  public function testCommentAsEntityReference(): void {
+    // Load the node and save it.
+    $edit = [
+      'entity_reference_comment' => $this->comment->id(),
+    ];
+    $this->drupalGet('node/' . $this->node2->id() . '/edit');
+    $this->submitForm($edit, 'Save');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains('has been updated');
+
+    // Make sure the comment is linked.
+    $this->assertSession()->pageTextContains($this->comment->label());
+  }
+
+  /**
+   * Tests that comments of unpublished are not shown.
+   */
+  public function testCommentOfUnpublishedNodeBypassAccess(): void {
+    // Unpublish the node that has the comment.
+    $this->node->setUnpublished()->save();
+
+    // When the user has 'bypass node access' permission, they can still set it.
+    $edit = [
+      'entity_reference_comment' => $this->comment->id(),
+    ];
+    $this->drupalGet('node/' . $this->node2->id() . '/edit');
+    $this->submitForm($edit, 'Save');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains('has been updated');
+
+    // Comment is seen as administrator user.
+    $this->assertSession()->pageTextContains($this->comment->label());
+
+    // But not as anonymous.
+    $this->drupalLogout();
+    $this->drupalGet('node/' . $this->node2->id());
+    $this->assertSession()->pageTextContains($this->node2->label());
+    $this->assertSession()->pageTextNotContains($this->comment->label());
+  }
+
+}

core/modules/comment/tests/src/Functional/CommentEntityTest.php

@@ -0,0 +1,98 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+use Drupal\comment\Entity\CommentType;
+use Drupal\comment\Plugin\Field\FieldType\CommentItemInterface;
+use Drupal\Core\Language\LanguageInterface;
+use Drupal\comment\CommentInterface;
+use Drupal\comment\Entity\Comment;
+use Drupal\Tests\taxonomy\Traits\TaxonomyTestTrait;
+
+/**
+ * Tests comments with other entities.
+ *
+ * @group comment
+ */
+class CommentEntityTest extends CommentTestBase {
+
+  use TaxonomyTestTrait;
+
+  /**
+   * Modules to install.
+   *
+   * @var array
+   */
+  protected static $modules = [
+    'block',
+    'comment',
+    'node',
+    'history',
+    'field_ui',
+    'datetime',
+    'taxonomy',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  protected $vocab;
+  protected $commentType;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->vocab = $this->createVocabulary();
+    $this->commentType = CommentType::create([
+      'id' => 'taxonomy_comment',
+      'label' => 'Taxonomy comment',
+      'description' => '',
+      'target_entity_type_id' => 'taxonomy_term',
+    ]);
+    $this->commentType->save();
+    $this->addDefaultCommentField(
+      'taxonomy_term',
+      $this->vocab->id(),
+      'field_comment',
+      CommentItemInterface::OPEN,
+      $this->commentType->id()
+    );
+  }
+
+  /**
+   * Tests CSS classes on comments.
+   */
+  public function testEntityChanges(): void {
+    $this->drupalLogin($this->webUser);
+    // Create a new node.
+    $term = $this->createTerm($this->vocab, ['uid' => $this->webUser->id()]);
+
+    // Add a comment.
+    /** @var \Drupal\comment\CommentInterface $comment */
+    $comment = Comment::create([
+      'entity_id' => $term->id(),
+      'entity_type' => 'taxonomy_term',
+      'field_name' => 'field_comment',
+      'uid' => $this->webUser->id(),
+      'status' => CommentInterface::PUBLISHED,
+      'subject' => $this->randomMachineName(),
+      'language' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
+      'comment_body' => [LanguageInterface::LANGCODE_NOT_SPECIFIED => [$this->randomMachineName()]],
+    ]);
+    $comment->save();
+
+    // Request the node with the comment.
+    $this->drupalGet('taxonomy/term/' . $term->id());
+    $settings = $this->getDrupalSettings();
+    $this->assertFalse(isset($settings['ajaxPageState']['libraries']) && in_array('comment/drupal.comment-new-indicator', explode(',', $settings['ajaxPageState']['libraries'])), 'drupal.comment-new-indicator library is present.');
+    $this->assertFalse(isset($settings['history']['lastReadTimestamps']) && in_array($term->id(), array_keys($settings['history']['lastReadTimestamps'])), 'history.lastReadTimestamps is present.');
+  }
+
+}

core/modules/comment/tests/src/Functional/CommentFieldsTest.php

@@ -0,0 +1,201 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+use Drupal\comment\Plugin\Field\FieldType\CommentItemInterface;
+use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\field\Entity\FieldConfig;
+use Drupal\comment\Entity\CommentType;
+
+/**
+ * Tests fields on comments.
+ *
+ * @group comment
+ */
+class CommentFieldsTest extends CommentTestBase {
+
+  /**
+   * Install the field UI.
+   *
+   * @var array
+   */
+  protected static $modules = ['field_ui'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Tests that the default 'comment_body' field is correctly added.
+   */
+  public function testCommentDefaultFields(): void {
+    // Do not make assumptions on default node types created by the test
+    // installation profile, and create our own.
+    $this->drupalCreateContentType(['type' => 'test_node_type']);
+    $this->addDefaultCommentField('node', 'test_node_type');
+
+    // Check that the 'comment_body' field is present on the comment bundle.
+    $field = FieldConfig::loadByName('comment', 'comment', 'comment_body');
+    $this->assertNotEmpty($field, 'The comment_body field is added when a comment bundle is created');
+
+    $field->delete();
+
+    // Check that the 'comment_body' field is not deleted since it is persisted
+    // even if it has no fields.
+    $field_storage = FieldStorageConfig::loadByName('comment', 'comment_body');
+    $this->assertInstanceOf(FieldStorageConfig::class, $field_storage);
+
+    // Create a new content type.
+    $type_name = 'test_node_type_2';
+    $this->drupalCreateContentType(['type' => $type_name]);
+    $this->addDefaultCommentField('node', $type_name);
+
+    // Check that the 'comment_body' field exists and has an instance on the
+    // new comment bundle.
+    $field_storage = FieldStorageConfig::loadByName('comment', 'comment_body');
+    $this->assertInstanceOf(FieldStorageConfig::class, $field_storage);
+    $field = FieldConfig::loadByName('comment', 'comment', 'comment_body');
+    $this->assertTrue(isset($field), "The comment_body field is present for comments on type $type_name");
+
+    // Test adding a field that defaults to CommentItemInterface::CLOSED.
+    $this->addDefaultCommentField('node', 'test_node_type', 'who_likes_ponies', CommentItemInterface::CLOSED, 'who_likes_ponies');
+    $field = FieldConfig::load('node.test_node_type.who_likes_ponies');
+    $this->assertEquals(CommentItemInterface::CLOSED, $field->getDefaultValueLiteral()[0]['status']);
+  }
+
+  /**
+   * Tests that you can remove a comment field.
+   */
+  public function testCommentFieldDelete(): void {
+    $this->drupalCreateContentType(['type' => 'test_node_type']);
+    $this->addDefaultCommentField('node', 'test_node_type');
+    // We want to test the handling of removing the primary comment field, so we
+    // ensure there is at least one other comment field attached to a node type
+    // so that comment_entity_load() runs for nodes.
+    $this->addDefaultCommentField('node', 'test_node_type', 'comment2');
+
+    // Create a sample node.
+    $node = $this->drupalCreateNode([
+      'title' => 'Baloney',
+      'type' => 'test_node_type',
+    ]);
+
+    $this->drupalLogin($this->webUser);
+
+    $this->drupalGet('node/' . $node->nid->value);
+    $elements = $this->cssSelect('.comment-form');
+    $this->assertCount(2, $elements, 'There are two comment fields on the node.');
+
+    // Delete the first comment field.
+    FieldStorageConfig::loadByName('node', 'comment')->delete();
+    $this->drupalGet('node/' . $node->nid->value);
+    $elements = $this->cssSelect('.comment-form');
+    $this->assertCount(1, $elements, 'There is one comment field on the node.');
+  }
+
+  /**
+   * Tests link building with non-default comment field names.
+   */
+  public function testCommentFieldLinksNonDefaultName(): void {
+    $this->drupalCreateContentType(['type' => 'test_node_type']);
+    $this->addDefaultCommentField('node', 'test_node_type', 'comment2');
+
+    $web_user2 = $this->drupalCreateUser([
+      'access comments',
+      'post comments',
+      'create article content',
+      'edit own comments',
+      'skip comment approval',
+      'access content',
+    ]);
+
+    // Create a sample node.
+    $node = $this->drupalCreateNode([
+      'title' => 'Baloney',
+      'type' => 'test_node_type',
+    ]);
+
+    // Go to the node first so that web_user2 see new comments.
+    $this->drupalLogin($web_user2);
+    $this->drupalGet($node->toUrl());
+    $this->drupalLogout();
+
+    // Test that buildCommentedEntityLinks() does not break when the 'comment'
+    // field does not exist. Requires at least one comment.
+    $this->drupalLogin($this->webUser);
+    $this->postComment($node, 'Here is a comment', '', NULL, 'comment2');
+    $this->drupalLogout();
+
+    $this->drupalLogin($web_user2);
+
+    // We want to check the attached drupalSettings of
+    // \Drupal\comment\CommentLinkBuilder::buildCommentedEntityLinks. Therefore
+    // we need a node listing, let's use views for that.
+    $this->container->get('module_installer')->install(['views'], TRUE);
+    $this->drupalGet('node');
+
+    $link_info = $this->getDrupalSettings()['comment']['newCommentsLinks']['node']['comment2']['2'];
+    $this->assertSame(1, $link_info['new_comment_count']);
+    $this->assertSame($node->toUrl('canonical', ['fragment' => 'new'])->toString(), $link_info['first_new_comment_link']);
+  }
+
+  /**
+   * Tests creating a comment field through the interface.
+   */
+  public function testCommentFieldCreate(): void {
+    // Create user who can administer user fields.
+    $user = $this->drupalCreateUser([
+      'administer user fields',
+    ]);
+    $this->drupalLogin($user);
+
+    // Create comment field in account settings.
+    $edit = [
+      'new_storage_type' => 'comment',
+    ];
+    $this->drupalGet('admin/config/people/accounts/fields/add-field');
+    $this->submitForm($edit, 'Continue');
+    $edit = [
+      'label' => 'User comment',
+      'field_name' => 'user_comment',
+    ];
+    $this->submitForm($edit, 'Continue');
+
+    // Try to save the comment field without selecting a comment type.
+    $edit = [];
+    $this->submitForm($edit, 'Update settings');
+    // We should get an error message.
+    $this->assertSession()->pageTextContains('The submitted value in the Comment type element is not allowed.');
+
+    // Create a comment type for users.
+    $bundle = CommentType::create([
+      'id' => 'user_comment_type',
+      'label' => 'user_comment_type',
+      'description' => '',
+      'target_entity_type_id' => 'user',
+    ]);
+    $bundle->save();
+
+    // Select a comment type and try to save again.
+    $edit = [
+      'field_storage[subform][settings][comment_type]' => 'user_comment_type',
+    ];
+    $this->drupalGet('admin/config/people/accounts/add-field/user/field_user_comment');
+    $this->submitForm($edit, 'Update settings');
+    // We shouldn't get an error message.
+    $this->assertSession()->pageTextNotContains('The submitted value in the Comment type element is not allowed.');
+
+    // Try to save the comment field with "Comments per page"
+    // setting value as zero.
+    $edit = [
+      'settings[per_page]' => 0,
+    ];
+    $this->drupalGet('admin/config/people/accounts/add-field/user/field_user_comment');
+    $this->submitForm($edit, 'Save settings');
+    $this->assertSession()->statusMessageContains('Saved User comment configuration.', 'status');
+  }
+
+}

core/modules/comment/tests/src/Functional/CommentInterfaceTest.php

@@ -0,0 +1,359 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+use Drupal\Core\Url;
+use Drupal\comment\CommentManagerInterface;
+use Drupal\comment\Plugin\Field\FieldType\CommentItemInterface;
+use Drupal\comment\Entity\Comment;
+use Drupal\Core\Entity\Entity\EntityViewDisplay;
+use Drupal\Core\Entity\Entity\EntityViewMode;
+use Drupal\field\Entity\FieldConfig;
+use Drupal\user\RoleInterface;
+use Drupal\filter\Entity\FilterFormat;
+
+/**
+ * Tests comment user interfaces.
+ *
+ * @group comment
+ */
+class CommentInterfaceTest extends CommentTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Set up comments to have subject and preview disabled.
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    // Make sure that comment field title is not displayed when there's no
+    // comments posted.
+    $this->drupalGet($this->node->toUrl());
+    $this->assertSession()->responseNotMatches('@<h2[^>]*>Comments</h2>@');
+
+    // Set comments to have subject and preview disabled.
+    $this->setCommentPreview(DRUPAL_DISABLED);
+    $this->setCommentForm(TRUE);
+    $this->setCommentSubject(FALSE);
+    $this->setCommentSettings('default_mode', CommentManagerInterface::COMMENT_MODE_THREADED, 'Comment paging changed.');
+  }
+
+  /**
+   * Tests the comment interface.
+   */
+  public function testCommentInterface(): void {
+
+    // Post comment #1 without subject or preview.
+    $this->drupalLogin($this->webUser);
+    $comment_text = $this->randomMachineName();
+    $comment = $this->postComment($this->node, $comment_text);
+    $this->assertTrue($this->commentExists($comment), 'Comment found.');
+
+    // Test that using an invalid entity-type does not raise an error.
+    $this->drupalGet('comment/reply/yeah-this-is-not-an-entity-type/' . $this->node->id() . '/comment/' . $comment->id());
+    $this->assertSession()->statusCodeEquals(404);
+
+    // Test the comment field title is displayed when there's comments.
+    $this->drupalGet($this->node->toUrl());
+    $this->assertSession()->responseMatches('@<h2[^>]*>Comments</h2>@');
+
+    // Set comments to have subject and preview to required.
+    $this->drupalLogout();
+    $this->setCommentSubject(TRUE);
+    $this->setCommentPreview(DRUPAL_REQUIRED);
+
+    // Create comment #2 that allows subject and requires preview.
+    $this->drupalLogin($this->webUser);
+    $subject_text = $this->randomMachineName();
+    $comment_text = $this->randomMachineName();
+    $comment = $this->postComment($this->node, $comment_text, $subject_text, TRUE);
+    $this->assertTrue($this->commentExists($comment), 'Comment found.');
+
+    // Comment as anonymous with preview required.
+    $this->drupalLogout();
+    user_role_grant_permissions(RoleInterface::ANONYMOUS_ID, ['access content', 'access comments', 'post comments', 'skip comment approval']);
+    $anonymous_comment = $this->postComment($this->node, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+    $this->assertTrue($this->commentExists($anonymous_comment), 'Comment found.');
+    $anonymous_comment->delete();
+
+    // Check comment display.
+    $this->drupalLogin($this->webUser);
+    $this->drupalGet('node/' . $this->node->id());
+    $this->assertSession()->pageTextContains($subject_text);
+    $this->assertSession()->pageTextContains($comment_text);
+    $this->assertSession()->elementExists('xpath', '//footer/a[contains(@href,"' . base_path() . 'comment/' . $comment->id() . '#comment-' . $comment->id() . '") and text()="Permalink"]');
+
+    // Set comments to have subject and preview to optional.
+    $this->drupalLogout();
+    $this->drupalLogin($this->adminUser);
+    $this->setCommentSubject(TRUE);
+    $this->setCommentPreview(DRUPAL_OPTIONAL);
+
+    $this->drupalGet('comment/' . $comment->id() . '/edit');
+    $this->assertSession()->titleEquals('Edit comment ' . $comment->getSubject() . ' | Drupal');
+
+    // Test changing the comment author to "Anonymous".
+    $comment = $this->postComment(NULL, $comment->comment_body->value, $comment->getSubject(), ['uid' => '']);
+    $this->assertSame('Anonymous', $comment->getAuthorName());
+    $this->assertEquals(0, $comment->getOwnerId());
+
+    // Test changing the comment author to an unverified user.
+    $random_name = $this->randomMachineName();
+    $this->drupalGet('comment/' . $comment->id() . '/edit');
+    $comment = $this->postComment(NULL, $comment->comment_body->value, $comment->getSubject(), ['name' => $random_name]);
+    $this->drupalGet('node/' . $this->node->id());
+    $this->assertSession()->pageTextContains($random_name . ' (not verified)');
+
+    // Test changing the comment author to a verified user.
+    $this->drupalGet('comment/' . $comment->id() . '/edit');
+    $comment = $this->postComment(NULL, $comment->comment_body->value, $comment->getSubject(), ['uid' => $this->webUser->getAccountName() . ' (' . $this->webUser->id() . ')']);
+    $this->assertSame($this->webUser->getAccountName(), $comment->getAuthorName());
+    $this->assertSame($this->webUser->id(), $comment->getOwnerId());
+
+    $this->drupalLogout();
+
+    // Reply to comment #2 creating comment #3 with optional preview and no
+    // subject though field enabled.
+    $this->drupalLogin($this->webUser);
+    // Deliberately use the wrong URL to test
+    // \Drupal\comment\Controller\CommentController::redirectNode().
+    $this->drupalGet('comment/' . $this->node->id() . '/reply');
+    // Verify we were correctly redirected.
+    $this->assertSession()->addressEquals(Url::fromRoute('comment.reply', ['entity_type' => 'node', 'entity' => $this->node->id(), 'field_name' => 'comment']));
+    $this->drupalGet('comment/reply/node/' . $this->node->id() . '/comment/' . $comment->id());
+    $this->assertSession()->pageTextContains($subject_text);
+    $this->assertSession()->pageTextContains($comment_text);
+    $reply = $this->postComment(NULL, $this->randomMachineName(), '', TRUE);
+    $reply_loaded = Comment::load($reply->id());
+    $this->assertTrue($this->commentExists($reply, TRUE), 'Reply found.');
+    $this->assertEquals($comment->id(), $reply_loaded->getParentComment()->id(), 'Pid of a reply to a comment is set correctly.');
+    // Check the thread of reply grows correctly.
+    $this->assertEquals(rtrim($comment->getThread(), '/') . '.00/', $reply_loaded->getThread());
+
+    // Second reply to comment #2 creating comment #4.
+    $this->drupalGet('comment/reply/node/' . $this->node->id() . '/comment/' . $comment->id());
+    $this->assertSession()->pageTextContains($comment->getSubject());
+    $this->assertSession()->pageTextContains($comment->comment_body->value);
+    $reply = $this->postComment(NULL, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+    $reply_loaded = Comment::load($reply->id());
+    $this->assertTrue($this->commentExists($reply, TRUE), 'Second reply found.');
+    // Check the thread of second reply grows correctly.
+    $this->assertEquals(rtrim($comment->getThread(), '/') . '.01/', $reply_loaded->getThread());
+
+    // Reply to comment #4 creating comment #5.
+    $this->drupalGet('comment/reply/node/' . $this->node->id() . '/comment/' . $reply_loaded->id());
+    $this->assertSession()->pageTextContains($reply_loaded->getSubject());
+    $this->assertSession()->pageTextContains($reply_loaded->comment_body->value);
+    $reply = $this->postComment(NULL, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+    $reply_loaded = Comment::load($reply->id());
+    $this->assertTrue($this->commentExists($reply, TRUE), 'Second reply found.');
+    // Check the thread of reply to second reply grows correctly.
+    $this->assertEquals(rtrim($comment->getThread(), '/') . '.01.00/', $reply_loaded->getThread());
+
+    // Edit reply.
+    $this->drupalGet('comment/' . $reply->id() . '/edit');
+    $reply = $this->postComment(NULL, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+    $this->assertTrue($this->commentExists($reply, TRUE), 'Modified reply found.');
+
+    // Confirm a new comment is posted to the correct page.
+    $this->setCommentsPerPage(2);
+    $comment_new_page = $this->postComment($this->node, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+    $this->assertTrue($this->commentExists($comment_new_page), 'Page one exists. %s');
+    $this->drupalGet('node/' . $this->node->id(), ['query' => ['page' => 2]]);
+    $this->assertTrue($this->commentExists($reply, TRUE), 'Page two exists. %s');
+    $this->setCommentsPerPage(50);
+
+    // Attempt to reply to an unpublished comment.
+    $reply_loaded->setUnpublished();
+    $reply_loaded->save();
+    $this->drupalGet('comment/reply/node/' . $this->node->id() . '/comment/' . $reply_loaded->id());
+    $this->assertSession()->statusCodeEquals(403);
+
+    // Attempt to post to node with comments disabled.
+    $this->node = $this->drupalCreateNode(['type' => 'article', 'promote' => 1, 'comment' => [['status' => CommentItemInterface::HIDDEN]]]);
+    $this->assertNotNull($this->node, 'Article node created.');
+    $this->drupalGet('comment/reply/node/' . $this->node->id() . '/comment');
+    $this->assertSession()->statusCodeEquals(403);
+    $this->assertSession()->fieldNotExists('edit-comment');
+
+    // Attempt to post to node with read-only comments.
+    $this->node = $this->drupalCreateNode(['type' => 'article', 'promote' => 1, 'comment' => [['status' => CommentItemInterface::CLOSED]]]);
+    $this->assertNotNull($this->node, 'Article node created.');
+    $this->drupalGet('comment/reply/node/' . $this->node->id() . '/comment');
+    $this->assertSession()->statusCodeEquals(403);
+    $this->assertSession()->fieldNotExists('edit-comment');
+
+    // Attempt to post to node with comments enabled (check field names etc).
+    $this->node = $this->drupalCreateNode(['type' => 'article', 'promote' => 1, 'comment' => [['status' => CommentItemInterface::OPEN]]]);
+    $this->assertNotNull($this->node, 'Article node created.');
+    $this->drupalGet('comment/reply/node/' . $this->node->id() . '/comment');
+    $this->assertSession()->pageTextNotContains('This discussion is closed');
+    // Ensure that the comment body field exists.
+    $this->assertSession()->fieldExists('edit-comment-body-0-value');
+
+    // Delete comment and make sure that reply is also removed.
+    $this->drupalLogout();
+    $this->drupalLogin($this->adminUser);
+    $this->deleteComment($comment);
+    $this->deleteComment($comment_new_page);
+
+    $this->drupalGet('node/' . $this->node->id());
+    $this->assertFalse($this->commentExists($comment), 'Comment not found.');
+    $this->assertFalse($this->commentExists($reply, TRUE), 'Reply not found.');
+
+    // Enabled comment form on node page.
+    $this->setCommentForm(TRUE);
+
+    // Submit comment through node form.
+    $this->drupalLogin($this->webUser);
+    $this->drupalGet('node/' . $this->node->id());
+    $form_comment = $this->postComment(NULL, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+    $this->assertTrue($this->commentExists($form_comment), 'Form comment found.');
+
+    // Disable comment form on node page.
+    $this->drupalLogout();
+    $this->setCommentForm(FALSE);
+  }
+
+  /**
+   * Tests that the subject is automatically filled if disabled or left blank.
+   *
+   * When the subject field is blank or disabled, the first 29 characters of the
+   * comment body are used for the subject. If this would break within a word,
+   * then the break is put at the previous word boundary instead.
+   */
+  public function testAutoFilledSubject(): void {
+    $this->drupalLogin($this->webUser);
+    $this->drupalGet('node/' . $this->node->id());
+
+    // Break when there is a word boundary before 29 characters.
+    $body_text = 'A quick brown fox jumped over the lazy dog';
+    $comment1 = $this->postComment(NULL, $body_text, '', TRUE);
+    $this->assertTrue($this->commentExists($comment1), 'Form comment found.');
+    $this->assertEquals('A quick brown fox jumped…', $comment1->getSubject());
+
+    // Break at 29 characters where there's no boundary before that.
+    $body_text2 = 'AQuickBrownFoxJumpedOverTheLazyDog';
+    $comment2 = $this->postComment(NULL, $body_text2, '', TRUE);
+    $this->assertEquals('AQuickBrownFoxJumpedOverTheL…', $comment2->getSubject());
+
+    // Make the body field non required.
+    $comment_body_field = FieldConfig::loadByName('comment', 'comment', 'comment_body');
+    $comment_body_field->setRequired(FALSE)->save();
+    // Try to post a comment without any value in body and subject fields.
+    $this->drupalGet('node/' . $this->node->id());
+    // Ensure that there are no PHP errors or warnings when automatically
+    // generating the subject. This occurs when the comment body is empty.
+    $comment2 = $this->postComment(NULL, '', '', TRUE);
+    $this->assertEquals('(No subject)', $comment2->getSubject());
+  }
+
+  /**
+   * Tests that automatic subject is correctly created from HTML comment text.
+   *
+   * This is the same test as in CommentInterfaceTest::testAutoFilledSubject()
+   * with the additional check that HTML is stripped appropriately prior to
+   * character-counting.
+   */
+  public function testAutoFilledHtmlSubject(): void {
+    // Set up two default (i.e. filtered HTML) input formats, because then we
+    // can select one of them. Then create a user that can use these formats,
+    // log the user in, and then GET the node page on which to test the
+    // comments.
+    $filtered_html_format = FilterFormat::create([
+      'format' => 'filtered_html',
+      'name' => 'Filtered HTML',
+    ]);
+    $filtered_html_format->save();
+    $full_html_format = FilterFormat::create([
+      'format' => 'full_html',
+      'name' => 'Full HTML',
+    ]);
+    $full_html_format->save();
+    $html_user = $this->drupalCreateUser([
+      'access comments',
+      'post comments',
+      'edit own comments',
+      'skip comment approval',
+      'access content',
+      $filtered_html_format->getPermissionName(),
+      $full_html_format->getPermissionName(),
+    ]);
+    $this->drupalLogin($html_user);
+    $this->drupalGet('node/' . $this->node->id());
+
+    // HTML should not be included in the character count.
+    $body_text1 = '<span></span><strong> </strong><span> </span><strong></strong>Hello World<br />';
+    $edit1 = [
+      'comment_body[0][value]' => $body_text1,
+      'comment_body[0][format]' => 'filtered_html',
+    ];
+    $this->submitForm($edit1, 'Save');
+    $this->assertEquals('Hello World', Comment::load(1)->getSubject());
+
+    // If there's nothing other than HTML, the subject should be '(No subject)'.
+    $body_text2 = '<span></span><strong> </strong><span> </span><strong></strong> <br />';
+    $edit2 = [
+      'comment_body[0][value]' => $body_text2,
+      'comment_body[0][format]' => 'filtered_html',
+    ];
+    $this->submitForm($edit2, 'Save');
+    $this->assertEquals('(No subject)', Comment::load(2)->getSubject());
+  }
+
+  /**
+   * Tests the comment formatter configured with a custom comment view mode.
+   */
+  public function testViewMode(): void {
+    $this->drupalLogin($this->webUser);
+    $this->drupalGet($this->node->toUrl());
+    $comment_text = $this->randomMachineName();
+    // Post a comment.
+    $this->postComment($this->node, $comment_text);
+
+    // Comment displayed in 'default' display mode found and has body text.
+    $comment_element = $this->cssSelect('#comment-1');
+    $this->assertNotEmpty($comment_element);
+    $this->assertSession()->responseContains('<p>' . $comment_text . '</p>');
+
+    // Create a new comment entity view mode.
+    $mode = $this->randomMachineName();
+    EntityViewMode::create([
+      'targetEntityType' => 'comment',
+      'id' => "comment.$mode",
+      'label' => 'Comment test',
+    ])->save();
+    // Create the corresponding entity view display for article node-type. Note
+    // that this new view display mode doesn't contain the comment body.
+    EntityViewDisplay::create([
+      'targetEntityType' => 'comment',
+      'bundle' => 'comment',
+      'mode' => $mode,
+    ])->setStatus(TRUE)->save();
+
+    /** @var \Drupal\Core\Entity\Display\EntityViewDisplayInterface $node_display */
+    $node_display = EntityViewDisplay::load('node.article.default');
+    $formatter = $node_display->getComponent('comment');
+    // Change the node comment field formatter to use $mode mode instead of
+    // 'default' mode.
+    $formatter['settings']['view_mode'] = $mode;
+    $node_display
+      ->setComponent('comment', $formatter)
+      ->save();
+
+    // Reloading the node page to show the same node with its same comment but
+    // with a different display mode.
+    $this->drupalGet($this->node->toUrl());
+    // The comment should exist but without the body text because we used $mode
+    // mode this time.
+    $comment_element = $this->cssSelect('#comment-1');
+    $this->assertNotEmpty($comment_element);
+    $this->assertSession()->responseNotContains('<p>' . $comment_text . '</p>');
+  }
+
+}

core/modules/comment/tests/src/Functional/CommentLanguageTest.php

@@ -0,0 +1,167 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+use Drupal\comment\Entity\Comment;
+use Drupal\comment\Plugin\Field\FieldType\CommentItemInterface;
+use Drupal\comment\Tests\CommentTestTrait;
+use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests for comment language.
+ *
+ * @group comment
+ */
+class CommentLanguageTest extends BrowserTestBase {
+
+  use CommentTestTrait;
+
+  /**
+   * Modules to install.
+   *
+   * We also use the language_test module here to be able to turn on content
+   * language negotiation. Drupal core does not provide a way in itself to do
+   * that.
+   *
+   * @var array
+   */
+  protected static $modules = [
+    'node',
+    'language',
+    'language_test',
+    'comment_test',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->drupalCreateContentType(['type' => 'article', 'name' => 'Article']);
+
+    // Create and log in user.
+    $admin_user = $this->drupalCreateUser([
+      'administer site configuration',
+      'administer languages',
+      'access administration pages',
+      'administer content types',
+      'administer comments',
+      'create article content',
+      'access comments',
+      'post comments',
+      'skip comment approval',
+    ]);
+    $this->drupalLogin($admin_user);
+
+    // Add language.
+    $edit = ['predefined_langcode' => 'fr'];
+    $this->drupalGet('admin/config/regional/language/add');
+    $this->submitForm($edit, 'Add language');
+
+    // Set "Article" content type to use multilingual support.
+    $edit = ['language_configuration[language_alterable]' => TRUE];
+    $this->drupalGet('admin/structure/types/manage/article');
+    $this->submitForm($edit, 'Save');
+
+    // Enable content language negotiation UI.
+    \Drupal::state()->set('language_test.content_language_type', TRUE);
+
+    // Set interface language detection to user and content language detection
+    // to URL. Disable inheritance from interface language to ensure content
+    // language will fall back to the default language if no URL language can be
+    // detected.
+    $edit = [
+      'language_interface[enabled][language-user]' => TRUE,
+      'language_content[enabled][language-url]' => TRUE,
+      'language_content[enabled][language-interface]' => FALSE,
+    ];
+    $this->drupalGet('admin/config/regional/language/detection');
+    $this->submitForm($edit, 'Save settings');
+
+    // Change user language preference, this way interface language is always
+    // French no matter what path prefix the URLs have.
+    $edit = ['preferred_langcode' => 'fr'];
+    $this->drupalGet("user/" . $admin_user->id() . "/edit");
+    $this->submitForm($edit, 'Save');
+
+    // Create comment field on article.
+    $this->addDefaultCommentField('node', 'article');
+
+    // Make comment body translatable.
+    $field_storage = FieldStorageConfig::loadByName('comment', 'comment_body');
+    $field_storage->setTranslatable(TRUE);
+    $field_storage->save();
+    $this->assertTrue($field_storage->isTranslatable(), 'Comment body is translatable.');
+  }
+
+  /**
+   * Tests that comment language is properly set.
+   */
+  public function testCommentLanguage(): void {
+
+    // Create two nodes, one for english and one for french, and comment each
+    // node using both english and french as content language by changing URL
+    // language prefixes. Meanwhile interface language is always French, which
+    // is the user language preference. This way we can ensure that node
+    // language and interface language do not influence comment language, as
+    // only content language has to.
+    foreach ($this->container->get('language_manager')->getLanguages() as $node_langcode => $node_language) {
+      // Create "Article" content.
+      $title = $this->randomMachineName();
+      $edit = [
+        'title[0][value]' => $title,
+        'body[0][value]' => $this->randomMachineName(),
+        'langcode[0][value]' => $node_langcode,
+        'comment[0][status]' => CommentItemInterface::OPEN,
+      ];
+      $this->drupalGet("node/add/article");
+      $this->submitForm($edit, 'Save');
+      $node = $this->drupalGetNodeByTitle($title);
+
+      $prefixes = $this->config('language.negotiation')->get('url.prefixes');
+      foreach ($this->container->get('language_manager')->getLanguages() as $langcode => $language) {
+        // Post a comment with content language $langcode.
+        $prefix = empty($prefixes[$langcode]) ? '' : $prefixes[$langcode] . '/';
+        $comment_values[$node_langcode][$langcode] = $this->randomMachineName();
+        $edit = [
+          'subject[0][value]' => $this->randomMachineName(),
+          'comment_body[0][value]' => $comment_values[$node_langcode][$langcode],
+        ];
+        $this->drupalGet($prefix . 'node/' . $node->id());
+        $this->submitForm($edit, 'Preview');
+        $this->submitForm($edit, 'Save');
+
+        // Check that comment language matches the current content language.
+        $cids = \Drupal::entityQuery('comment')
+          ->accessCheck(FALSE)
+          ->condition('entity_id', $node->id())
+          ->condition('entity_type', 'node')
+          ->condition('field_name', 'comment')
+          ->sort('cid', 'DESC')
+          ->range(0, 1)
+          ->execute();
+        $comment = Comment::load(reset($cids));
+        $this->assertEquals($langcode, $comment->langcode->value, "The comment posted with content language $langcode and belonging to the node with language $node_langcode has language {$comment->langcode->value}");
+        $this->assertEquals($comment_values[$node_langcode][$langcode], $comment->comment_body->value, 'Comment body correctly stored.');
+      }
+    }
+
+    // Check that comment bodies appear in the administration UI.
+    $this->drupalGet('admin/content/comment');
+    foreach ($comment_values as $node_values) {
+      foreach ($node_values as $value) {
+        $this->assertSession()->responseContains($value);
+      }
+    }
+  }
+
+}

core/modules/comment/tests/src/Functional/CommentLinksAlterTest.php

@@ -0,0 +1,45 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+/**
+ * Tests comment links altering.
+ *
+ * @group comment
+ */
+class CommentLinksAlterTest extends CommentTestBase {
+
+  protected static $modules = ['comment_test'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // Enable comment_test.module's hook_comment_links_alter() implementation.
+    $this->container->get('state')->set('comment_test_links_alter_enabled', TRUE);
+  }
+
+  /**
+   * Tests comment links altering.
+   */
+  public function testCommentLinksAlter(): void {
+    $this->drupalLogin($this->webUser);
+    $comment_text = $this->randomMachineName();
+    $subject = $this->randomMachineName();
+    $this->postComment($this->node, $comment_text, $subject);
+
+    $this->drupalGet('node/' . $this->node->id());
+
+    $this->assertSession()->linkExists('Report');
+  }
+
+}

core/modules/comment/tests/src/Functional/CommentLinksTest.php

@@ -0,0 +1,159 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+use Drupal\comment\Plugin\Field\FieldType\CommentItemInterface;
+use Drupal\Core\Language\LanguageInterface;
+use Drupal\comment\CommentInterface;
+use Drupal\comment\CommentManagerInterface;
+use Drupal\user\RoleInterface;
+use Drupal\comment\Entity\Comment;
+
+/**
+ * Basic comment links tests to ensure markup present.
+ *
+ * @group comment
+ */
+class CommentLinksTest extends CommentTestBase {
+
+  /**
+   * Comment being tested.
+   *
+   * @var \Drupal\comment\CommentInterface
+   */
+  protected $comment;
+
+  /**
+   * Seen comments, array of comment IDs.
+   *
+   * @var array
+   */
+  protected $seen = [];
+
+  /**
+   * Use the main node listing to test rendering on teasers.
+   *
+   * @var array
+   *
+   * @todo Remove this dependency.
+   */
+  protected static $modules = ['views'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Tests that comment links are output and can be hidden.
+   */
+  public function testCommentLinks(): void {
+    // Remove additional user permissions from $this->webUser added by setUp(),
+    // since this test is limited to anonymous and authenticated roles only.
+    $roles = $this->webUser->getRoles();
+    \Drupal::entityTypeManager()->getStorage('user_role')->load(reset($roles))->delete();
+
+    // Create a comment via CRUD API functionality, since
+    // $this->postComment() relies on actual user permissions.
+    $comment = Comment::create([
+      'cid' => NULL,
+      'entity_id' => $this->node->id(),
+      'entity_type' => 'node',
+      'field_name' => 'comment',
+      'pid' => 0,
+      'uid' => 0,
+      'status' => CommentInterface::PUBLISHED,
+      'subject' => $this->randomMachineName(),
+      'hostname' => '127.0.0.1',
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
+      'comment_body' => [['value' => $this->randomMachineName()]],
+    ]);
+    $comment->save();
+    $this->comment = $comment;
+
+    // Tests that reply link is not visible when threading is disabled.
+    $this->drupalLogin($this->webUser);
+    $this->setCommentSettings('default_mode', CommentManagerInterface::COMMENT_MODE_FLAT, 'Comment paging changed.');
+    $this->drupalGet('node/' . $this->node->id());
+    $this->assertSession()->linkNotExists('Reply');
+    // Tests that reply link is visible when threading is enabled.
+    $this->setCommentSettings('default_mode', CommentManagerInterface::COMMENT_MODE_THREADED, 'Comment paging changed.');
+    $this->drupalGet('node/' . $this->node->id());
+    $this->assertSession()->linkExists('Reply');
+
+    // Change comment settings.
+    $this->setCommentSettings('form_location', CommentItemInterface::FORM_BELOW, 'Set comment form location');
+    $this->node->comment = CommentItemInterface::OPEN;
+    $this->node->save();
+
+    // Change user permissions.
+    $perms = [
+      'access comments' => 1,
+      'post comments' => 1,
+      'skip comment approval' => 1,
+      'edit own comments' => 1,
+    ];
+    user_role_change_permissions(RoleInterface::ANONYMOUS_ID, $perms);
+
+    $nid = $this->node->id();
+
+    // Assert basic link is output, actual functionality is unit-tested in
+    // \Drupal\comment\Tests\CommentLinkBuilderTest.
+    foreach (['node', "node/$nid"] as $path) {
+      $this->drupalGet($path);
+
+      // In teaser view, a link containing the comment count is always
+      // expected.
+      if ($path == 'node') {
+        $this->assertSession()->linkExists('1 comment');
+      }
+      $this->assertSession()->linkExists('Add new comment');
+    }
+
+    $display_repository = $this->container->get('entity_display.repository');
+
+    // Change weight to make links go before comment body.
+    $display_repository->getViewDisplay('comment', 'comment')
+      ->setComponent('links', ['weight' => -100])
+      ->save();
+    $this->drupalGet($this->node->toUrl());
+    $element = $this->cssSelect('article.js-comment > div');
+    // Get last child element.
+    $element = end($element);
+    $this->assertSame('div', $element->getTagName(), 'Last element is comment body.');
+
+    // Change weight to make links go after comment body.
+    $display_repository->getViewDisplay('comment', 'comment')
+      ->setComponent('links', ['weight' => 100])
+      ->save();
+    $this->drupalGet($this->node->toUrl());
+    $element = $this->cssSelect('article.js-comment > div');
+    // Get last child element.
+    $element = end($element);
+    $this->assertNotEmpty($element->find('css', 'ul.links'), 'Last element is comment links.');
+
+    // Make sure we can hide node links.
+    $display_repository->getViewDisplay('node', $this->node->bundle())
+      ->removeComponent('links')
+      ->save();
+    $this->drupalGet($this->node->toUrl());
+    $this->assertSession()->linkNotExists('1 comment');
+    $this->assertSession()->linkNotExists('Add new comment');
+
+    // Visit the full node, make sure there are links for the comment.
+    $this->drupalGet('node/' . $this->node->id());
+    $this->assertSession()->pageTextContains($comment->getSubject());
+    $this->assertSession()->linkExists('Reply');
+
+    // Make sure we can hide comment links.
+    $display_repository->getViewDisplay('comment', 'comment')
+      ->removeComponent('links')
+      ->save();
+    $this->drupalGet('node/' . $this->node->id());
+    $this->assertSession()->pageTextContains($comment->getSubject());
+    $this->assertSession()->linkNotExists('Reply');
+  }
+
+}

core/modules/comment/tests/src/Functional/CommentNewIndicatorTest.php

@@ -0,0 +1,144 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+use Drupal\Component\Serialization\Json;
+use Drupal\Core\Language\LanguageInterface;
+use Drupal\comment\CommentInterface;
+use Drupal\Core\Url;
+use Drupal\comment\Entity\Comment;
+
+/**
+ * Tests the 'new' indicator posted on comments.
+ *
+ * @group comment
+ */
+class CommentNewIndicatorTest extends CommentTestBase {
+
+  /**
+   * Use the main node listing to test rendering on teasers.
+   *
+   * @var array
+   *
+   * @todo Remove this dependency.
+   */
+  protected static $modules = ['views'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Get node "x new comments" metadata from the server for the current user.
+   *
+   * @param array $node_ids
+   *   An array of node IDs.
+   *
+   * @return \Psr\Http\Message\ResponseInterface
+   *   The HTTP response.
+   */
+  protected function renderNewCommentsNodeLinks(array $node_ids) {
+    $client = $this->getHttpClient();
+    $url = Url::fromRoute('comment.new_comments_node_links');
+
+    return $client->request('POST', $this->buildUrl($url), [
+      'cookies' => $this->getSessionCookies(),
+      'http_errors' => FALSE,
+      'form_params' => [
+        'node_ids' => $node_ids,
+        'field_name' => 'comment',
+      ],
+    ]);
+  }
+
+  /**
+   * Tests new comment marker.
+   */
+  public function testCommentNewCommentsIndicator(): void {
+    // Test if the right links are displayed when no comment is present for the
+    // node.
+    $this->drupalLogin($this->adminUser);
+    $this->drupalGet('node');
+    $this->assertSession()->linkNotExists('0 comments');
+    $this->assertSession()->linkExists('Read more');
+    // Verify the data-history-node-last-comment-timestamp attribute, which is
+    // used by the drupal.node-new-comments-link library to determine whether
+    // a "x new comments" link might be necessary or not. We do this in
+    // JavaScript to prevent breaking the render cache.
+    $this->assertSession()->elementNotExists('xpath', '//*[@data-history-node-last-comment-timestamp]');
+
+    // Create a new comment. This helper function may be run with different
+    // comment settings so use $comment->save() to avoid complex setup.
+    /** @var \Drupal\comment\CommentInterface $comment */
+    $comment = Comment::create([
+      'cid' => NULL,
+      'entity_id' => $this->node->id(),
+      'entity_type' => 'node',
+      'field_name' => 'comment',
+      'pid' => 0,
+      'uid' => $this->loggedInUser->id(),
+      'status' => CommentInterface::PUBLISHED,
+      'subject' => $this->randomMachineName(),
+      'hostname' => '127.0.0.1',
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
+      'comment_body' => [LanguageInterface::LANGCODE_NOT_SPECIFIED => [$this->randomMachineName()]],
+    ]);
+    $comment->save();
+    $this->drupalLogout();
+
+    // Log in with 'web user' and check comment links.
+    $this->drupalLogin($this->webUser);
+    $this->drupalGet('node');
+    // Verify the data-history-node-last-comment-timestamp attribute. Given its
+    // value, the drupal.node-new-comments-link library would determine that the
+    // node received a comment after the user last viewed it, and hence it would
+    // perform an HTTP request to render the "new comments" node link.
+    $this->assertSession()->elementsCount('xpath', '//*[@data-history-node-last-comment-timestamp="' . $comment->getChangedTime() . '"]', 1);
+    $this->assertSession()->elementsCount('xpath', '//*[@data-history-node-field-name="comment"]', 1);
+    // The data will be pre-seeded on this particular page in drupalSettings, to
+    // avoid the need for the client to make a separate request to the server.
+    $settings = $this->getDrupalSettings();
+    $this->assertEquals(['lastReadTimestamps' => [1 => 0]], $settings['history']);
+    $this->assertEquals([
+      'newCommentsLinks' => [
+        'node' => [
+          'comment' => [
+            1 => [
+              'new_comment_count' => 1,
+              'first_new_comment_link' => Url::fromRoute('entity.node.canonical', ['node' => 1])->setOptions([
+                'fragment' => 'new',
+              ])->toString(),
+            ],
+          ],
+        ],
+      ],
+    ], $settings['comment']);
+    // Pretend the data was not present in drupalSettings, i.e. test the
+    // separate request to the server.
+    $response = $this->renderNewCommentsNodeLinks([$this->node->id()]);
+    $this->assertSame(200, $response->getStatusCode());
+    $json = Json::decode($response->getBody());
+    $expected = [
+      $this->node->id() => [
+        'new_comment_count' => 1,
+        'first_new_comment_link' => $this->node->toUrl('canonical', ['fragment' => 'new'])->toString(),
+      ],
+    ];
+    $this->assertSame($expected, $json);
+
+    // Failing to specify node IDs for the endpoint should return a 404.
+    $response = $this->renderNewCommentsNodeLinks([]);
+    $this->assertSame(404, $response->getStatusCode());
+
+    // Accessing the endpoint as the anonymous user should return a 403.
+    $this->drupalLogout();
+    $response = $this->renderNewCommentsNodeLinks([$this->node->id()]);
+    $this->assertSame(403, $response->getStatusCode());
+    $response = $this->renderNewCommentsNodeLinks([]);
+    $this->assertSame(403, $response->getStatusCode());
+  }
+
+}

core/modules/comment/tests/src/Functional/CommentNodeAccessTest.php

@@ -0,0 +1,90 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+use Drupal\comment\CommentManagerInterface;
+
+/**
+ * Tests comments with node access.
+ *
+ * Verifies there is no PostgreSQL error when viewing a node with threaded
+ * comments (a comment and a reply), if a node access module is in use.
+ *
+ * @group comment
+ */
+class CommentNodeAccessTest extends CommentTestBase {
+
+  /**
+   * Modules to install.
+   *
+   * @var array
+   */
+  protected static $modules = ['node_access_test'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    node_access_rebuild();
+
+    // Re-create user.
+    $this->webUser = $this->drupalCreateUser([
+      'access comments',
+      'post comments',
+      'create article content',
+      'edit own comments',
+      'node test view',
+      'skip comment approval',
+    ]);
+
+    // Set the author of the created node to the web_user uid.
+    $this->node->setOwnerId($this->webUser->id())->save();
+  }
+
+  /**
+   * Tests that threaded comments can be viewed.
+   */
+  public function testThreadedCommentView(): void {
+    // Set comments to have subject required and preview disabled.
+    $this->setCommentPreview(DRUPAL_DISABLED);
+    $this->setCommentForm(TRUE);
+    $this->setCommentSubject(TRUE);
+    $this->setCommentSettings('default_mode', CommentManagerInterface::COMMENT_MODE_THREADED, 'Comment paging changed.');
+
+    // Post comment.
+    $this->drupalLogin($this->webUser);
+    $comment_text = $this->randomMachineName();
+    $comment_subject = $this->randomMachineName();
+    $comment = $this->postComment($this->node, $comment_text, $comment_subject);
+    $this->assertTrue($this->commentExists($comment), 'Comment found.');
+
+    // Check comment display.
+    $this->drupalGet('node/' . $this->node->id());
+    $this->assertSession()->pageTextContains($comment_subject);
+    $this->assertSession()->pageTextContains($comment_text);
+
+    // Reply to comment, creating second comment.
+    $this->drupalGet('comment/reply/node/' . $this->node->id() . '/comment/' . $comment->id());
+    $reply_text = $this->randomMachineName();
+    $reply_subject = $this->randomMachineName();
+    $reply = $this->postComment(NULL, $reply_text, $reply_subject, TRUE);
+    $this->assertTrue($this->commentExists($reply, TRUE), 'Reply found.');
+
+    // Go to the node page and verify comment and reply are visible.
+    $this->drupalGet('node/' . $this->node->id());
+    $this->assertSession()->pageTextContains($comment_text);
+    $this->assertSession()->pageTextContains($comment_subject);
+    $this->assertSession()->pageTextContains($reply_text);
+    $this->assertSession()->pageTextContains($reply_subject);
+  }
+
+}

core/modules/comment/tests/src/Functional/CommentNodeChangesTest.php

@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+use Drupal\comment\Entity\Comment;
+use Drupal\field\Entity\FieldConfig;
+use Drupal\field\Entity\FieldStorageConfig;
+
+/**
+ * Tests that comments behave correctly when the node is changed.
+ *
+ * @group comment
+ */
+class CommentNodeChangesTest extends CommentTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Tests that comments are deleted with the node.
+   */
+  public function testNodeDeletion(): void {
+    $this->drupalLogin($this->webUser);
+    $comment = $this->postComment($this->node, $this->randomMachineName(), $this->randomMachineName());
+    $this->assertInstanceOf(Comment::class, $comment);
+    $this->node->delete();
+    $this->assertNull(Comment::load($comment->id()), 'The comment could not be loaded after the node was deleted.');
+    // Make sure the comment field storage and all its fields are deleted when
+    // the node type is deleted.
+    $this->assertNotNull(FieldStorageConfig::load('node.comment'), 'Comment field storage exists');
+    $this->assertNotNull(FieldConfig::load('node.article.comment'), 'Comment field exists');
+    // Delete the node type.
+    $this->node->get('type')->entity->delete();
+    $this->assertNull(FieldStorageConfig::load('node.comment'), 'Comment field storage deleted');
+    $this->assertNull(FieldConfig::load('node.article.comment'), 'Comment field deleted');
+  }
+
+}

core/modules/comment/tests/src/Functional/CommentNonNodeTest.php

@@ -0,0 +1,555 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+use Drupal\comment\CommentInterface;
+use Drupal\comment\Entity\Comment;
+use Drupal\comment\Entity\CommentType;
+use Drupal\comment\Plugin\Field\FieldType\CommentItemInterface;
+use Drupal\comment\Tests\CommentTestTrait;
+use Drupal\entity_test\Entity\EntityTest;
+use Drupal\field\Entity\FieldConfig;
+use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\Tests\BrowserTestBase;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Tests\field_ui\Traits\FieldUiTestTrait;
+use Drupal\user\RoleInterface;
+
+/**
+ * Tests commenting on a test entity.
+ *
+ * @group comment
+ */
+class CommentNonNodeTest extends BrowserTestBase {
+
+  use FieldUiTestTrait;
+  use CommentTestTrait;
+
+  protected static $modules = [
+    'comment',
+    'user',
+    'field_ui',
+    'entity_test',
+    'block',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * An administrative user with permission to configure comment settings.
+   *
+   * @var \Drupal\user\UserInterface
+   */
+  protected $adminUser;
+
+  /**
+   * The entity to use within tests.
+   *
+   * @var \Drupal\entity_test\Entity\EntityTest
+   */
+  protected $entity;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->drupalPlaceBlock('system_breadcrumb_block');
+    $this->drupalPlaceBlock('page_title_block');
+
+    // Create a bundle for entity_test.
+    entity_test_create_bundle('entity_test', 'Entity Test', 'entity_test');
+    CommentType::create([
+      'id' => 'comment',
+      'label' => 'Comment settings',
+      'description' => 'Comment settings',
+      'target_entity_type_id' => 'entity_test',
+    ])->save();
+    // Create comment field on entity_test bundle.
+    $this->addDefaultCommentField('entity_test', 'entity_test');
+
+    // Verify that bundles are defined correctly.
+    $bundles = \Drupal::service('entity_type.bundle.info')->getBundleInfo('comment');
+    $this->assertEquals('Comment settings', $bundles['comment']['label']);
+
+    // Create test user.
+    $this->adminUser = $this->drupalCreateUser([
+      'administer comments',
+      'skip comment approval',
+      'post comments',
+      'access comments',
+      'view test entity',
+      'administer entity_test content',
+    ]);
+
+    // Enable anonymous and authenticated user comments.
+    user_role_grant_permissions(RoleInterface::ANONYMOUS_ID, [
+      'access comments',
+      'post comments',
+      'skip comment approval',
+    ]);
+    user_role_grant_permissions(RoleInterface::AUTHENTICATED_ID, [
+      'access comments',
+      'post comments',
+      'skip comment approval',
+    ]);
+
+    // Create a test entity.
+    $random_label = $this->randomMachineName();
+    $data = ['type' => 'entity_test', 'name' => $random_label];
+    $this->entity = EntityTest::create($data);
+    $this->entity->save();
+  }
+
+  /**
+   * Posts a comment.
+   *
+   * @param \Drupal\Core\Entity\EntityInterface|null $entity
+   *   Entity to post comment on or NULL to post to the previously loaded page.
+   * @param string $comment
+   *   Comment body.
+   * @param string $subject
+   *   Comment subject.
+   * @param mixed $contact
+   *   Set to NULL for no contact info, TRUE to ignore success checking, and
+   *   array of values to set contact info.
+   *
+   * @return \Drupal\comment\CommentInterface
+   *   The new comment entity.
+   */
+  public function postComment(?EntityInterface $entity, $comment, $subject = '', $contact = NULL) {
+    $edit = [];
+    $edit['comment_body[0][value]'] = $comment;
+
+    $field = FieldConfig::loadByName('entity_test', 'entity_test', 'comment');
+    $preview_mode = $field->getSetting('preview');
+
+    // Must get the page before we test for fields.
+    if ($entity !== NULL) {
+      $this->drupalGet('comment/reply/entity_test/' . $entity->id() . '/comment');
+    }
+
+    // Determine the visibility of subject form field.
+    $display_repository = $this->container->get('entity_display.repository');
+    if ($display_repository->getFormDisplay('comment', 'comment')->getComponent('subject')) {
+      // Subject input allowed.
+      $edit['subject[0][value]'] = $subject;
+    }
+    else {
+      $this->assertSession()->fieldValueNotEquals('subject[0][value]', '');
+    }
+
+    if ($contact !== NULL && is_array($contact)) {
+      $edit += $contact;
+    }
+    switch ($preview_mode) {
+      case DRUPAL_REQUIRED:
+        // Preview required so no save button should be found.
+        $this->assertSession()->buttonNotExists('Save');
+        $this->submitForm($edit, 'Preview');
+        // Don't break here so that we can test post-preview field presence and
+        // function below.
+      case DRUPAL_OPTIONAL:
+        $this->assertSession()->buttonExists('Preview');
+        $this->assertSession()->buttonExists('Save');
+        $this->submitForm($edit, 'Save');
+        break;
+
+      case DRUPAL_DISABLED:
+        $this->assertSession()->buttonNotExists('Preview');
+        $this->assertSession()->buttonExists('Save');
+        $this->submitForm($edit, 'Save');
+        break;
+    }
+    $match = [];
+    // Get comment ID
+    preg_match('/#comment-([0-9]+)/', $this->getURL(), $match);
+
+    // Get comment.
+    if ($contact !== TRUE) {
+      // If true then attempting to find error message.
+      if ($subject) {
+        $this->assertSession()->pageTextContains($subject);
+      }
+      $this->assertSession()->pageTextContains($comment);
+      // Check the comment ID was extracted.
+      $this->assertArrayHasKey(1, $match);
+    }
+
+    return Comment::load($match[1]);
+  }
+
+  /**
+   * Checks current page for specified comment.
+   *
+   * @param \Drupal\comment\CommentInterface $comment
+   *   The comment object.
+   * @param bool $reply
+   *   Boolean indicating whether the comment is a reply to another comment.
+   *
+   * @return bool
+   *   Boolean indicating whether the comment was found.
+   */
+  public function commentExists(?CommentInterface $comment = NULL, $reply = FALSE) {
+    if ($comment) {
+      $regex = '/' . ($reply ? '<div class="indented">(.*?)' : '');
+      $regex .= '<article(.*?)id="comment-' . $comment->id() . '"(.*?)';
+      $regex .= $comment->getSubject() . '(.*?)';
+      $regex .= $comment->comment_body->value . '(.*?)';
+      $regex .= '/s';
+
+      return (boolean) preg_match($regex, $this->getSession()->getPage()->getContent());
+    }
+    else {
+      return FALSE;
+    }
+  }
+
+  /**
+   * Checks whether the commenter's contact information is displayed.
+   *
+   * @return bool
+   *   Contact info is available.
+   */
+  public function commentContactInfoAvailable() {
+    return (bool) preg_match('/(input).*?(name="name").*?(input).*?(name="mail").*?(input).*?(name="homepage")/s', $this->getSession()->getPage()->getContent());
+  }
+
+  /**
+   * Performs the specified operation on the specified comment.
+   *
+   * @param object $comment
+   *   Comment to perform operation on.
+   * @param string $operation
+   *   Operation to perform.
+   * @param bool $approval
+   *   Operation is found on approval page.
+   */
+  public function performCommentOperation($comment, $operation, $approval = FALSE) {
+    $edit = [];
+    $edit['operation'] = $operation;
+    $edit['comments[' . $comment->id() . ']'] = TRUE;
+    $this->drupalGet('admin/content/comment' . ($approval ? '/approval' : ''));
+    $this->submitForm($edit, 'Update');
+
+    if ($operation == 'delete') {
+      $this->submitForm([], 'Delete');
+      $this->assertSession()->pageTextContains('Deleted 1 comment.');
+    }
+    else {
+      $this->assertSession()->pageTextContains('The update has been performed.');
+    }
+  }
+
+  /**
+   * Gets the comment ID for an unapproved comment.
+   *
+   * @param string $subject
+   *   Comment subject to find.
+   *
+   * @return int
+   *   Comment ID.
+   */
+  public function getUnapprovedComment($subject) {
+    $this->drupalGet('admin/content/comment/approval');
+    preg_match('/href="(.*?)#comment-([^"]+)"(.*?)>(' . $subject . ')/', $this->getSession()->getPage()->getContent(), $match);
+
+    return $match[2];
+  }
+
+  /**
+   * Tests anonymous comment functionality.
+   */
+  public function testCommentFunctionality(): void {
+    $limited_user = $this->drupalCreateUser([
+      'administer entity_test fields',
+    ]);
+    $this->drupalLogin($limited_user);
+    // Test that default field exists.
+    $this->drupalGet('entity_test/structure/entity_test/fields');
+    $this->assertSession()->pageTextContains('Comments');
+    $this->assertSession()->linkByHrefExists('entity_test/structure/entity_test/fields/entity_test.entity_test.comment');
+    // Test widget hidden option is not visible when there's no comments.
+    $this->drupalGet('entity_test/structure/entity_test/fields/entity_test.entity_test.comment');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->fieldNotExists('edit-default-value-input-comment-und-0-status-0');
+    // Test that field to change cardinality is not available.
+    $this->assertSession()->fieldNotExists('cardinality_number');
+    $this->assertSession()->fieldNotExists('cardinality');
+
+    $this->drupalLogin($this->adminUser);
+
+    // Test breadcrumb on comment add page.
+    $this->drupalGet('comment/reply/entity_test/' . $this->entity->id() . '/comment');
+    $this->assertSession()->elementTextEquals('xpath', '//nav[@aria-labelledby="system-breadcrumb"]/ol/li[last()]/a', $this->entity->label());
+
+    // Post a comment.
+    /** @var \Drupal\comment\CommentInterface $comment1 */
+    $comment1 = $this->postComment($this->entity, $this->randomMachineName(), $this->randomMachineName());
+    $this->assertTrue($this->commentExists($comment1), 'Comment on test entity exists.');
+
+    // Test breadcrumb on comment reply page.
+    $this->drupalGet('comment/reply/entity_test/' . $this->entity->id() . '/comment/' . $comment1->id());
+    $this->assertSession()->elementTextEquals('xpath', '//nav[@aria-labelledby="system-breadcrumb"]/ol/li[last()]/a', $comment1->getSubject());
+
+    // Test breadcrumb on comment edit page.
+    $this->drupalGet('comment/' . $comment1->id() . '/edit');
+    $this->assertSession()->elementTextEquals('xpath', '//nav[@aria-labelledby="system-breadcrumb"]/ol/li[last()]/a', $comment1->getSubject());
+
+    // Test breadcrumb on comment delete page.
+    $this->drupalGet('comment/' . $comment1->id() . '/delete');
+    $this->assertSession()->elementTextEquals('xpath', '//nav[@aria-labelledby="system-breadcrumb"]/ol/li[last()]/a', $comment1->getSubject());
+
+    // Test threading replying to comment #1 creating comment #1_2.
+    $this->drupalGet('comment/reply/entity_test/' . $this->entity->id() . '/comment/' . $comment1->id());
+    $comment1_2 = $this->postComment(NULL, $this->randomMachineName(), $this->randomMachineName());
+    $this->assertTrue($this->commentExists($comment1_2, TRUE), 'Comment #1_2. Reply found.');
+    $this->assertEquals('01.00/', $comment1_2->getThread());
+
+    // Test nested threading replying to comment #1_2 creating comment #1_2_3.
+    $this->drupalGet('comment/reply/entity_test/' . $this->entity->id() . '/comment/' . $comment1_2->id());
+    $comment1_2_3 = $this->postComment(NULL, $this->randomMachineName(), $this->randomMachineName());
+    $this->assertTrue($this->commentExists($comment1_2_3, TRUE), 'Comment #1_2_3. Reply found.');
+    $this->assertEquals('01.00.00/', $comment1_2_3->getThread());
+
+    // Unpublish the comment.
+    $this->performCommentOperation($comment1, 'unpublish');
+    $this->drupalGet('admin/content/comment/approval');
+    $this->assertSession()->responseContains('comments[' . $comment1->id() . ']');
+
+    // Publish the comment.
+    $this->performCommentOperation($comment1, 'publish', TRUE);
+    $this->drupalGet('admin/content/comment');
+    $this->assertSession()->responseContains('comments[' . $comment1->id() . ']');
+
+    // Delete the comment.
+    $this->performCommentOperation($comment1, 'delete');
+    $this->drupalGet('admin/content/comment');
+    $this->assertSession()->responseNotContains('comments[' . $comment1->id() . ']');
+
+    // Post another comment.
+    $comment1 = $this->postComment($this->entity, $this->randomMachineName(), $this->randomMachineName());
+    $this->assertTrue($this->commentExists($comment1), 'Comment on test entity exists.');
+
+    // Check that the comment was found.
+    $this->drupalGet('admin/content/comment');
+    $this->assertSession()->responseContains('comments[' . $comment1->id() . ']');
+
+    // Check that entity access applies to administrative page.
+    $this->assertSession()->pageTextContains($this->entity->label());
+    $limited_user = $this->drupalCreateUser([
+      'administer comments',
+    ]);
+    $this->drupalLogin($limited_user);
+    $this->drupalGet('admin/content/comment');
+    $this->assertSession()->pageTextNotContains($this->entity->label());
+
+    $this->drupalLogout();
+
+    // Deny anonymous users access to comments.
+    user_role_change_permissions(RoleInterface::ANONYMOUS_ID, [
+      'access comments' => FALSE,
+      'post comments' => FALSE,
+      'skip comment approval' => FALSE,
+      'view test entity' => TRUE,
+    ]);
+
+    // Attempt to view comments while disallowed.
+    $this->drupalGet('entity-test/' . $this->entity->id());
+    // Verify that comments were not displayed.
+    $this->assertSession()->responseNotMatches('@<h2[^>]*>Comments</h2>@');
+    $this->assertSession()->linkNotExists('Add new comment', 'Link to add comment was found.');
+
+    // Attempt to view test entity comment form while disallowed.
+    $this->drupalGet('comment/reply/entity_test/' . $this->entity->id() . '/comment');
+    $this->assertSession()->statusCodeEquals(403);
+    $this->assertSession()->fieldNotExists('subject[0][value]');
+    $this->assertSession()->fieldNotExists('comment_body[0][value]');
+
+    user_role_change_permissions(RoleInterface::ANONYMOUS_ID, [
+      'access comments' => TRUE,
+      'post comments' => FALSE,
+      'view test entity' => TRUE,
+      'skip comment approval' => FALSE,
+    ]);
+    $this->drupalGet('entity_test/' . $this->entity->id());
+    // Verify that the comment field title is displayed.
+    $this->assertSession()->responseMatches('@<h2[^>]*>Comments</h2>@');
+    $this->assertSession()->linkExists('Log in', 0, 'Link to login was found.');
+    $this->assertSession()->linkExists('register', 0, 'Link to register was found.');
+    $this->assertSession()->fieldNotExists('subject[0][value]');
+    $this->assertSession()->fieldNotExists('comment_body[0][value]');
+
+    // Test the combination of anonymous users being able to post, but not view
+    // comments, to ensure that access to post comments doesn't grant access to
+    // view them.
+    user_role_change_permissions(RoleInterface::ANONYMOUS_ID, [
+      'access comments' => FALSE,
+      'post comments' => TRUE,
+      'skip comment approval' => TRUE,
+      'view test entity' => TRUE,
+    ]);
+    $this->drupalGet('entity_test/' . $this->entity->id());
+    // Verify that comments were not displayed.
+    $this->assertSession()->responseNotMatches('@<h2[^>]*>Comments</h2>@');
+    $this->assertSession()->fieldValueEquals('subject[0][value]', '');
+    $this->assertSession()->fieldValueEquals('comment_body[0][value]', '');
+
+    $this->drupalGet('comment/reply/entity_test/' . $this->entity->id() . '/comment/' . $comment1->id());
+    $this->assertSession()->statusCodeEquals(403);
+    $this->assertSession()->pageTextNotContains($comment1->getSubject());
+
+    // Test comment field widget changes.
+    $limited_user = $this->drupalCreateUser([
+      'administer entity_test fields',
+      'view test entity',
+      'administer entity_test content',
+      'administer comments',
+    ]);
+    $this->drupalLogin($limited_user);
+    $this->drupalGet('entity_test/structure/entity_test/fields/entity_test.entity_test.comment');
+    $this->assertSession()->checkboxNotChecked('edit-default-value-input-comment-0-status-0');
+    $this->assertSession()->checkboxNotChecked('edit-default-value-input-comment-0-status-1');
+    $this->assertSession()->checkboxChecked('edit-default-value-input-comment-0-status-2');
+    // Test comment option change in field settings.
+    $edit = [
+      'default_value_input[comment][0][status]' => CommentItemInterface::CLOSED,
+      'settings[anonymous]' => CommentInterface::ANONYMOUS_MAY_CONTACT,
+    ];
+    $this->submitForm($edit, 'Save settings');
+    $this->drupalGet('entity_test/structure/entity_test/fields/entity_test.entity_test.comment');
+    $this->assertSession()->checkboxNotChecked('edit-default-value-input-comment-0-status-0');
+    $this->assertSession()->checkboxChecked('edit-default-value-input-comment-0-status-1');
+    $this->assertSession()->checkboxNotChecked('edit-default-value-input-comment-0-status-2');
+    $this->assertSession()->fieldValueEquals('settings[anonymous]', CommentInterface::ANONYMOUS_MAY_CONTACT);
+
+    // Add a new comment-type.
+    $bundle = CommentType::create([
+      'id' => 'foobar',
+      'label' => 'Foobar',
+      'description' => '',
+      'target_entity_type_id' => 'entity_test',
+    ]);
+    $bundle->save();
+
+    // Add a new comment field.
+    $storage_edit = [
+      'settings[comment_type]' => 'foobar',
+    ];
+    $this->fieldUIAddNewField('entity_test/structure/entity_test', 'foobar', 'Foobar', 'comment', $storage_edit);
+
+    // Add a third comment field.
+    $this->fieldUIAddNewField('entity_test/structure/entity_test', 'bar_foo', 'Bar_Foo', 'comment', $storage_edit);
+
+    // Check the field contains the correct comment type.
+    $field_storage = FieldStorageConfig::load('entity_test.field_bar_foo');
+    $this->assertInstanceOf(FieldStorageConfig::class, $field_storage);
+    $this->assertEquals('foobar', $field_storage->getSetting('comment_type'));
+    $this->assertEquals(1, $field_storage->getCardinality());
+
+    // Test the new entity commenting inherits default.
+    $random_label = $this->randomMachineName();
+    $data = ['bundle' => 'entity_test', 'name' => $random_label];
+    $new_entity = EntityTest::create($data);
+    $new_entity->save();
+    $this->drupalGet('entity_test/manage/' . $new_entity->id() . '/edit');
+    $this->assertSession()->checkboxChecked('edit-field-foobar-0-status-2');
+    $this->assertSession()->checkboxNotChecked('edit-field-foobar-0-status-0');
+    $this->assertSession()->fieldNotExists('edit-field-foobar-0-status-1');
+
+    // @todo Check proper URL and form https://www.drupal.org/node/2458323
+    $this->drupalGet('comment/reply/entity_test/comment/' . $new_entity->id());
+    $this->assertSession()->fieldNotExists('subject[0][value]');
+    $this->assertSession()->fieldNotExists('comment_body[0][value]');
+
+    // Test removal of comment_body field.
+    $limited_user = $this->drupalCreateUser([
+      'administer entity_test fields',
+      'post comments',
+      'administer comment fields',
+      'administer comment types',
+      'view test entity',
+    ]);
+    $this->drupalLogin($limited_user);
+
+    $this->drupalGet('comment/reply/entity_test/' . $this->entity->id() . '/comment');
+    $this->assertSession()->fieldValueEquals('comment_body[0][value]', '');
+    $this->fieldUIDeleteField('admin/structure/comment/manage/comment', 'comment.comment.comment_body', 'Comment', 'Comment settings', 'comment type');
+    $this->drupalGet('comment/reply/entity_test/' . $this->entity->id() . '/comment');
+    $this->assertSession()->fieldNotExists('comment_body[0][value]');
+    // Set subject field to autogenerate it.
+    $edit = ['subject[0][value]' => ''];
+    $this->submitForm($edit, 'Save');
+  }
+
+  /**
+   * Tests comment fields cannot be added to entity types without integer IDs.
+   */
+  public function testsNonIntegerIdEntities(): void {
+    // Create a bundle for entity_test_string_id.
+    entity_test_create_bundle('entity_test', 'Entity Test', 'entity_test_string_id');
+    $limited_user = $this->drupalCreateUser([
+      'administer entity_test_string_id fields',
+      'administer comment types',
+    ]);
+    $this->drupalLogin($limited_user);
+    // Visit the Field UI field add page.
+    $this->drupalGet('entity_test_string_id/structure/entity_test/fields/add-field');
+    // Ensure field isn't shown for string IDs.
+    $this->assertSession()->elementNotExists('css', "[name='new_storage_type'][value='comment']");
+    // Ensure a core field type shown.
+    $this->assertSession()->elementExists('css', "[name='new_storage_type'][value='boolean']");
+
+    // Attempt to add a comment-type referencing this entity-type.
+    $this->drupalGet('admin/structure/comment/types/add');
+    $this->assertSession()->optionNotExists('edit-target-entity-type-id', 'entity_test_string_id');
+    $this->assertSession()->responseNotContains('Test entity with string_id');
+
+    // Create a bundle for entity_test_no_id.
+    entity_test_create_bundle('entity_test', 'Entity Test', 'entity_test_no_id');
+    $this->drupalLogin($this->drupalCreateUser([
+      'administer entity_test_no_id fields',
+    ]));
+    // Visit the Field UI field add page.
+    $this->drupalGet('entity_test_no_id/structure/entity_test/fields/add-field');
+    // Ensure field isn't shown for empty IDs.
+    $this->assertSession()->elementNotExists('css', "[name='new_storage_type'][value='comment']");
+    // Ensure a core field type shown.
+    $this->assertSession()->elementExists('css', "[name='new_storage_type'][value='boolean']");
+  }
+
+  /**
+   * Ensures that comment settings are not required.
+   */
+  public function testCommentSettingsNotRequired(): void {
+    $limited_user = $this->drupalCreateUser([
+      'administer entity_test fields',
+    ]);
+    $this->drupalLogin($limited_user);
+    $this->drupalGet('entity_test/structure/entity_test/fields/entity_test.entity_test.comment');
+
+    // Change the comments to be displayed as hidden by default.
+    $edit = [
+      'default_value_input[comment][0][status]' => CommentItemInterface::HIDDEN,
+      'settings[anonymous]' => CommentInterface::ANONYMOUS_MAY_CONTACT,
+    ];
+    $this->submitForm($edit, 'Save settings');
+
+    // Ensure that the comment settings field is not required and can be saved
+    // with the default value.
+    $this->drupalLogin($this->adminUser);
+    $this->drupalGet('/entity_test/add');
+    $this->assertSession()->checkboxChecked('edit-comment-0-status-0');
+    $edit = [
+      "name[0][value]" => 'Comment test',
+    ];
+    $this->submitForm($edit, 'Save');
+    $this->assertSession()->pageTextContains('entity_test 2 has been created.');
+  }
+
+}

core/modules/comment/tests/src/Functional/CommentPagerTest.php

@@ -0,0 +1,453 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+use Drupal\comment\CommentManagerInterface;
+use Drupal\Component\Render\FormattableMarkup;
+use Drupal\node\Entity\Node;
+
+/**
+ * Tests paging of comments and their settings.
+ *
+ * @group comment
+ */
+class CommentPagerTest extends CommentTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Confirms comment paging works correctly with flat and threaded comments.
+   */
+  public function testCommentPaging(): void {
+    $this->drupalLogin($this->adminUser);
+
+    // Set comment variables.
+    $this->setCommentForm(TRUE);
+    $this->setCommentSubject(TRUE);
+    $this->setCommentPreview(DRUPAL_DISABLED);
+
+    // Create a node and three comments.
+    $node = $this->drupalCreateNode(['type' => 'article', 'promote' => 1]);
+    $comments = [];
+    $comments[] = $this->postComment($node, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+    $comments[] = $this->postComment($node, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+    $comments[] = $this->postComment($node, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+
+    $this->setCommentSettings('default_mode', CommentManagerInterface::COMMENT_MODE_FLAT, 'Comment paging changed.');
+
+    // Set "Comments per page" as zero and verify that all comments are appearing
+    // on the page.
+    $this->setCommentsPerPage(0);
+    $this->drupalGet('node/' . $node->id());
+    $this->assertTrue($this->commentExists($comments[0]), 'Comment 1 appears on page.');
+    $this->assertTrue($this->commentExists($comments[1]), 'Comment 2 appears on page.');
+    $this->assertTrue($this->commentExists($comments[2]), 'Comment 3 appears on page.');
+
+    // Set comments to one per page so that we are able to test paging without
+    // needing to insert large numbers of comments.
+    $this->setCommentsPerPage(1);
+
+    // Check the first page of the node, and confirm the correct comments are
+    // shown.
+    $this->drupalGet('node/' . $node->id());
+    $this->assertSession()->pageTextContains('next');
+    $this->assertTrue($this->commentExists($comments[0]), 'Comment 1 appears on page 1.');
+    $this->assertFalse($this->commentExists($comments[1]), 'Comment 2 does not appear on page 1.');
+    $this->assertFalse($this->commentExists($comments[2]), 'Comment 3 does not appear on page 1.');
+
+    // Check the second page.
+    $this->drupalGet('node/' . $node->id(), ['query' => ['page' => 1]]);
+    $this->assertTrue($this->commentExists($comments[1]), 'Comment 2 appears on page 2.');
+    $this->assertFalse($this->commentExists($comments[0]), 'Comment 1 does not appear on page 2.');
+    $this->assertFalse($this->commentExists($comments[2]), 'Comment 3 does not appear on page 2.');
+
+    // Check the third page.
+    $this->drupalGet('node/' . $node->id(), ['query' => ['page' => 2]]);
+    $this->assertTrue($this->commentExists($comments[2]), 'Comment 3 appears on page 3.');
+    $this->assertFalse($this->commentExists($comments[0]), 'Comment 1 does not appear on page 3.');
+    $this->assertFalse($this->commentExists($comments[1]), 'Comment 2 does not appear on page 3.');
+
+    // Post a reply to the oldest comment and test again.
+    $oldest_comment = reset($comments);
+    $this->drupalGet('comment/reply/node/' . $node->id() . '/comment/' . $oldest_comment->id());
+    $reply = $this->postComment(NULL, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+
+    $this->setCommentsPerPage(2);
+    // We are still in flat view - the replies should not be on the first page,
+    // even though they are replies to the oldest comment.
+    $this->drupalGet('node/' . $node->id(), ['query' => ['page' => 0]]);
+    $this->assertFalse($this->commentExists($reply, TRUE), 'In flat mode, reply does not appear on page 1.');
+
+    // If we switch to threaded mode, the replies on the oldest comment
+    // should be bumped to the first page and comment 6 should be bumped
+    // to the second page.
+    $this->setCommentSettings('default_mode', CommentManagerInterface::COMMENT_MODE_THREADED, 'Switched to threaded mode.');
+    $this->drupalGet('node/' . $node->id(), ['query' => ['page' => 0]]);
+    $this->assertTrue($this->commentExists($reply, TRUE), 'In threaded mode, reply appears on page 1.');
+    $this->assertFalse($this->commentExists($comments[1]), 'In threaded mode, comment 2 has been bumped off of page 1.');
+
+    // If (# replies > # comments per page) in threaded expanded view,
+    // the overage should be bumped.
+    $reply2 = $this->postComment(NULL, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+    $this->drupalGet('node/' . $node->id(), ['query' => ['page' => 0]]);
+    $this->assertFalse($this->commentExists($reply2, TRUE), 'In threaded mode where # replies > # comments per page, the newest reply does not appear on page 1.');
+
+    // Test that the page build process does not somehow generate errors when
+    // # comments per page is set to 0.
+    $this->setCommentsPerPage(0);
+    $this->drupalGet('node/' . $node->id(), ['query' => ['page' => 0]]);
+    $this->assertFalse($this->commentExists($reply2, TRUE), 'Threaded mode works correctly when comments per page is 0.');
+    // Test that all main comments are appearing in the threaded mode.
+    $this->assertTrue($this->commentExists($comments[0]), 'Comment 1 appears on page.');
+    $this->assertTrue($this->commentExists($comments[1]), 'Comment 2 appears on page.');
+    $this->assertTrue($this->commentExists($comments[2]), 'Comment 3 appears on page.');
+
+    $this->drupalLogout();
+  }
+
+  /**
+   * Confirms comment paging works correctly with flat and threaded comments.
+   */
+  public function testCommentPermalink(): void {
+    $this->drupalLogin($this->adminUser);
+
+    // Set comment variables.
+    $this->setCommentForm(TRUE);
+    $this->setCommentSubject(TRUE);
+    $this->setCommentPreview(DRUPAL_DISABLED);
+
+    // Create a node and three comments.
+    $node = $this->drupalCreateNode(['type' => 'article', 'promote' => 1]);
+    $comments = [];
+    $comments[] = $this->postComment($node, 'comment 1: ' . $this->randomMachineName(), $this->randomMachineName(), TRUE);
+    $comments[] = $this->postComment($node, 'comment 2: ' . $this->randomMachineName(), $this->randomMachineName(), TRUE);
+    $comments[] = $this->postComment($node, 'comment 3: ' . $this->randomMachineName(), $this->randomMachineName(), TRUE);
+
+    $this->setCommentSettings('default_mode', CommentManagerInterface::COMMENT_MODE_FLAT, 'Comment paging changed.');
+
+    // Set comments to one per page so that we are able to test paging without
+    // needing to insert large numbers of comments.
+    $this->setCommentsPerPage(1);
+
+    // Navigate to each comment permalink as anonymous and assert it appears on
+    // the page.
+    foreach ($comments as $index => $comment) {
+      $this->drupalGet($comment->toUrl());
+      $this->assertTrue($this->commentExists($comment), sprintf('Comment %d appears on page %d.', $index + 1, $index + 1));
+    }
+  }
+
+  /**
+   * Tests comment ordering and threading.
+   */
+  public function testCommentOrderingThreading(): void {
+    $this->drupalLogin($this->adminUser);
+
+    // Set comment variables.
+    $this->setCommentForm(TRUE);
+    $this->setCommentSubject(TRUE);
+    $this->setCommentPreview(DRUPAL_DISABLED);
+
+    // Display all the comments on the same page.
+    $this->setCommentsPerPage(1000);
+
+    // Create a node and three comments.
+    $node = $this->drupalCreateNode(['type' => 'article', 'promote' => 1]);
+    $comments = [];
+    $comments[] = $this->postComment($node, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+    $comments[] = $this->postComment($node, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+    $comments[] = $this->postComment($node, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+
+    // Post a reply to the second comment.
+    $this->drupalGet('comment/reply/node/' . $node->id() . '/comment/' . $comments[1]->id());
+    $comments[] = $this->postComment(NULL, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+
+    // Post a reply to the first comment.
+    $this->drupalGet('comment/reply/node/' . $node->id() . '/comment/' . $comments[0]->id());
+    $comments[] = $this->postComment(NULL, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+
+    // Post a reply to the last comment.
+    $this->drupalGet('comment/reply/node/' . $node->id() . '/comment/' . $comments[2]->id());
+    $comments[] = $this->postComment(NULL, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+
+    // Post a reply to the second comment.
+    $this->drupalGet('comment/reply/node/' . $node->id() . '/comment/' . $comments[3]->id());
+    $comments[] = $this->postComment(NULL, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+
+    // At this point, the comment tree is:
+    // - 0
+    //   - 4
+    // - 1
+    //   - 3
+    //     - 6
+    // - 2
+    //   - 5
+
+    $this->setCommentSettings('default_mode', CommentManagerInterface::COMMENT_MODE_FLAT, 'Comment paging changed.');
+
+    $expected_order = [
+      0,
+      1,
+      2,
+      3,
+      4,
+      5,
+      6,
+    ];
+    $this->drupalGet('node/' . $node->id());
+    $this->assertCommentOrder($comments, $expected_order);
+
+    $this->setCommentSettings('default_mode', CommentManagerInterface::COMMENT_MODE_THREADED, 'Switched to threaded mode.');
+
+    $expected_order = [
+      0,
+      4,
+      1,
+      3,
+      6,
+      2,
+      5,
+    ];
+    $this->drupalGet('node/' . $node->id());
+    $this->assertCommentOrder($comments, $expected_order);
+  }
+
+  /**
+   * Asserts that the comments are displayed in the correct order.
+   *
+   * @param \Drupal\comment\CommentInterface[] $comments
+   *   An array of comments, must be of the type CommentInterface.
+   * @param array $expected_order
+   *   An array of keys from $comments describing the expected order.
+   *
+   * @internal
+   */
+  public function assertCommentOrder(array $comments, array $expected_order): void {
+    $expected_cids = [];
+
+    // First, rekey the expected order by cid.
+    foreach ($expected_order as $key) {
+      $expected_cids[] = $comments[$key]->id();
+    }
+
+    $comment_anchors = $this->xpath('//article[starts-with(@id,"comment-")]');
+    $result_order = [];
+    foreach ($comment_anchors as $anchor) {
+      $result_order[] = substr($anchor->getAttribute('id'), 8);
+    }
+    $this->assertEquals($expected_cids, $result_order, sprintf('Comment order: expected %s, returned %s.', implode(',', $expected_cids), implode(',', $result_order)));
+  }
+
+  /**
+   * Tests calculation of first page with new comment.
+   */
+  public function testCommentNewPageIndicator(): void {
+    $this->drupalLogin($this->adminUser);
+
+    // Set comment variables.
+    $this->setCommentForm(TRUE);
+    $this->setCommentSubject(TRUE);
+    $this->setCommentPreview(DRUPAL_DISABLED);
+
+    // Set comments to one per page so that we are able to test paging without
+    // needing to insert large numbers of comments.
+    $this->setCommentsPerPage(1);
+
+    // Create a node and three comments.
+    $node = $this->drupalCreateNode(['type' => 'article', 'promote' => 1]);
+    $comments = [];
+    $comments[] = $this->postComment($node, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+    $comments[] = $this->postComment($node, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+    $comments[] = $this->postComment($node, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+
+    // Post a reply to the second comment.
+    $this->drupalGet('comment/reply/node/' . $node->id() . '/comment/' . $comments[1]->id());
+    $comments[] = $this->postComment(NULL, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+
+    // Post a reply to the first comment.
+    $this->drupalGet('comment/reply/node/' . $node->id() . '/comment/' . $comments[0]->id());
+    $comments[] = $this->postComment(NULL, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+
+    // Post a reply to the last comment.
+    $this->drupalGet('comment/reply/node/' . $node->id() . '/comment/' . $comments[2]->id());
+    $comments[] = $this->postComment(NULL, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+
+    // At this point, the comment tree is:
+    // - 0
+    //   - 4
+    // - 1
+    //   - 3
+    // - 2
+    //   - 5
+
+    $this->setCommentSettings('default_mode', CommentManagerInterface::COMMENT_MODE_FLAT, 'Comment paging changed.');
+
+    $expected_pages = [
+      // Page of comment 5
+      1 => 5,
+      // Page of comment 4
+      2 => 4,
+      // Page of comment 3
+      3 => 3,
+      // Page of comment 2
+      4 => 2,
+      // Page of comment 1
+      5 => 1,
+      // Page of comment 0
+      6 => 0,
+    ];
+
+    $node = Node::load($node->id());
+    foreach ($expected_pages as $new_replies => $expected_page) {
+      $returned_page = \Drupal::entityTypeManager()->getStorage('comment')
+        ->getNewCommentPageNumber($node->get('comment')->comment_count, $new_replies, $node, 'comment');
+      $this->assertSame($expected_page, $returned_page, "Flat mode, $new_replies replies: expected page $expected_page, returned page $returned_page.");
+    }
+
+    $this->setCommentSettings('default_mode', CommentManagerInterface::COMMENT_MODE_THREADED, 'Switched to threaded mode.');
+
+    $expected_pages = [
+      // Page of comment 5
+      1 => 5,
+      // Page of comment 4
+      2 => 1,
+      // Page of comment 4
+      3 => 1,
+      // Page of comment 4
+      4 => 1,
+      // Page of comment 4
+      5 => 1,
+      // Page of comment 0
+      6 => 0,
+    ];
+
+    \Drupal::entityTypeManager()->getStorage('node')->resetCache([$node->id()]);
+    $node = Node::load($node->id());
+    foreach ($expected_pages as $new_replies => $expected_page) {
+      $returned_page = \Drupal::entityTypeManager()->getStorage('comment')
+        ->getNewCommentPageNumber($node->get('comment')->comment_count, $new_replies, $node, 'comment');
+      $this->assertEquals($expected_page, $returned_page, "Threaded mode, $new_replies replies: expected page $expected_page, returned page $returned_page.");
+    }
+  }
+
+  /**
+   * Confirms comment paging works correctly with two pagers.
+   */
+  public function testTwoPagers(): void {
+    // Add another field to article content-type.
+    $this->addDefaultCommentField('node', 'article', 'comment_2');
+    // Set default to display comment list with unique pager id.
+    \Drupal::service('entity_display.repository')
+      ->getViewDisplay('node', 'article')
+      ->setComponent('comment_2', [
+        'label' => 'hidden',
+        'type' => 'comment_default',
+        'weight' => 30,
+        'settings' => [
+          'pager_id' => 1,
+          'view_mode' => 'default',
+        ],
+      ])
+      ->save();
+
+    // Make sure pager appears in formatter summary and settings form.
+    $account = $this->drupalCreateUser(['administer node display']);
+    $this->drupalLogin($account);
+    $this->drupalGet('admin/structure/types/manage/article/display');
+    // No summary for standard pager.
+    $this->assertSession()->pageTextNotContains('Pager ID: 0');
+    $this->assertSession()->pageTextContains('Pager ID: 1');
+    $this->submitForm([], 'comment_settings_edit');
+    // Change default pager to 2.
+    $this->submitForm(['fields[comment][settings_edit_form][settings][pager_id]' => 2], 'Save');
+    $this->assertSession()->pageTextContains('Pager ID: 2');
+    // Revert the changes.
+    $this->submitForm([], 'comment_settings_edit');
+    $this->submitForm(['fields[comment][settings_edit_form][settings][pager_id]' => 0], 'Save');
+    // No summary for standard pager.
+    $this->assertSession()->pageTextNotContains('Pager ID: 0');
+
+    $this->drupalLogin($this->adminUser);
+
+    // Add a new node with both comment fields open.
+    $node = $this->drupalCreateNode(['type' => 'article', 'promote' => 1, 'uid' => $this->webUser->id()]);
+    // Set comment options.
+    $comments = [];
+    foreach (['comment', 'comment_2'] as $field_name) {
+      $this->setCommentForm(TRUE, $field_name);
+      $this->setCommentPreview(DRUPAL_OPTIONAL, $field_name);
+      $this->setCommentSettings('default_mode', CommentManagerInterface::COMMENT_MODE_FLAT, 'Comment paging changed.', $field_name);
+
+      // Set comments to one per page so that we are able to test paging without
+      // needing to insert large numbers of comments.
+      $this->setCommentsPerPage(1, $field_name);
+      for ($i = 1; $i <= 4; $i++) {
+        $comment = "Comment $i on field $field_name";
+        $comments[] = $this->postComment($node, $comment, $comment, TRUE, $field_name);
+      }
+    }
+
+    // Check the first page of the node, and confirm the correct comments are
+    // shown.
+    $this->drupalGet('node/' . $node->id());
+    $this->assertSession()->pageTextContains('next');
+    $this->assertSession()->pageTextContains('Comment 1 on field comment');
+    $this->assertSession()->pageTextContains('Comment 1 on field comment_2');
+    // Navigate to next page of field 1.
+    $this->clickLinkWithXPath('//h3/a[normalize-space(text())=:label]/ancestor::section[1]//a[@rel="next"]', [':label' => 'Comment 1 on field comment']);
+    // Check only one pager updated.
+    $this->assertSession()->pageTextContains('Comment 2 on field comment');
+    $this->assertSession()->pageTextContains('Comment 1 on field comment_2');
+    // Return to page 1.
+    $this->drupalGet('node/' . $node->id());
+    // Navigate to next page of field 2.
+    $this->clickLinkWithXPath('//h3/a[normalize-space(text())=:label]/ancestor::section[1]//a[@rel="next"]', [':label' => 'Comment 1 on field comment_2']);
+    // Check only one pager updated.
+    $this->assertSession()->pageTextContains('Comment 1 on field comment');
+    $this->assertSession()->pageTextContains('Comment 2 on field comment_2');
+    // Navigate to next page of field 1.
+    $this->clickLinkWithXPath('//h3/a[normalize-space(text())=:label]/ancestor::section[1]//a[@rel="next"]', [':label' => 'Comment 1 on field comment']);
+    // Check only one pager updated.
+    $this->assertSession()->pageTextContains('Comment 2 on field comment');
+    $this->assertSession()->pageTextContains('Comment 2 on field comment_2');
+  }
+
+  /**
+   * Follows a link found at a give xpath query.
+   *
+   * Will click the first link found with the given xpath query by default,
+   * or a later one if an index is given.
+   *
+   * If the link is discovered and clicked, the test passes. Fail otherwise.
+   *
+   * @param string $xpath
+   *   Xpath query that targets an anchor tag, or set of anchor tags.
+   * @param array $arguments
+   *   An array of arguments with keys in the form ':name' matching the
+   *   placeholders in the query. The values may be either strings or numeric
+   *   values.
+   * @param int $index
+   *   Link position counting from zero.
+   *
+   * @return string|false
+   *   Page contents on success, or FALSE on failure.
+   *
+   * @see \Drupal\Tests\UiHelperTrait::clickLink()
+   */
+  protected function clickLinkWithXPath($xpath, $arguments = [], $index = 0) {
+    $url_before = $this->getUrl();
+    $urls = $this->xpath($xpath, $arguments);
+    if (isset($urls[$index])) {
+      $url_target = $this->getAbsoluteUrl($urls[$index]->getAttribute('href'));
+      return $this->drupalGet($url_target);
+    }
+    $this->fail(new FormattableMarkup('Link %label does not exist on @url_before', ['%label' => $xpath, '@url_before' => $url_before]));
+    return FALSE;
+  }
+
+}

core/modules/comment/tests/src/Functional/CommentPreviewTest.php

@@ -0,0 +1,227 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+use Drupal\comment\CommentManagerInterface;
+use Drupal\Component\Render\MarkupInterface;
+use Drupal\Core\Datetime\DrupalDateTime;
+use Drupal\comment\Entity\Comment;
+use Drupal\Tests\TestFileCreationTrait;
+
+/**
+ * Tests comment preview.
+ *
+ * @group comment
+ */
+class CommentPreviewTest extends CommentTestBase {
+
+  use TestFileCreationTrait {
+    getTestFiles as drupalGetTestFiles;
+  }
+
+  /**
+   * Modules to install.
+   *
+   * @var array
+   */
+  protected static $modules = ['olivero_test', 'test_user_config'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'olivero';
+
+  /**
+   * Tests comment preview.
+   */
+  public function testCommentPreview(): void {
+    $this->setCommentPreview(DRUPAL_OPTIONAL);
+    $this->setCommentForm(TRUE);
+    $this->setCommentSubject(TRUE);
+    $this->setCommentSettings('default_mode', CommentManagerInterface::COMMENT_MODE_THREADED, 'Comment paging changed.');
+
+    // Log in as web user.
+    $this->drupalLogin($this->webUser);
+
+    // Test escaping of the username on the preview form.
+    \Drupal::service('module_installer')->install(['user_hooks_test']);
+    \Drupal::state()->set('user_hooks_test_user_format_name_alter', TRUE);
+    $edit = [];
+    $edit['subject[0][value]'] = $this->randomMachineName(8);
+    $edit['comment_body[0][value]'] = $this->randomMachineName(16);
+    $this->drupalGet('node/' . $this->node->id());
+    $this->submitForm($edit, 'Preview');
+    $this->assertSession()->assertEscaped('<em>' . $this->webUser->id() . '</em>');
+
+    \Drupal::state()->set('user_hooks_test_user_format_name_alter_safe', TRUE);
+    $this->drupalGet('node/' . $this->node->id());
+    $this->submitForm($edit, 'Preview');
+    $this->assertInstanceOf(MarkupInterface::class, $this->webUser->getDisplayName());
+    $this->assertSession()->assertNoEscaped('<em>' . $this->webUser->id() . '</em>');
+    $this->assertSession()->responseContains('<em>' . $this->webUser->id() . '</em>');
+
+    // Add a user picture.
+    $image = current($this->drupalGetTestFiles('image'));
+    $user_edit['files[user_picture_0]'] = \Drupal::service('file_system')->realpath($image->uri);
+    $this->drupalGet('user/' . $this->webUser->id() . '/edit');
+    $this->submitForm($user_edit, 'Save');
+
+    // As the web user, fill in the comment form and preview the comment.
+    $this->drupalGet('node/' . $this->node->id());
+    $this->submitForm($edit, 'Preview');
+
+    // Check that the preview is displaying the title and body.
+    $this->assertSession()->titleEquals('Preview comment | Drupal');
+    $this->assertSession()->pageTextContains($edit['subject[0][value]']);
+    $this->assertSession()->pageTextContains($edit['comment_body[0][value]']);
+
+    // Check that the title and body fields are displayed with the correct values.
+    $this->assertSession()->fieldValueEquals('subject[0][value]', $edit['subject[0][value]']);
+    $this->assertSession()->fieldValueEquals('comment_body[0][value]', $edit['comment_body[0][value]']);
+
+    // Check that the user picture is displayed.
+    $this->assertSession()->elementExists('xpath', "//article[contains(@class, 'preview')]//div[contains(@class, 'user-picture')]//img");
+
+    // Ensure that preview node is displayed after the submit buttons of the form.
+    $xpath = $this->assertSession()->buildXPathQuery('//div[@id=:id]/following-sibling::article', [':id' => 'edit-actions']);
+    $this->assertSession()->elementExists('xpath', $xpath);
+  }
+
+  /**
+   * Tests comment preview.
+   */
+  public function testCommentPreviewDuplicateSubmission(): void {
+    $this->setCommentPreview(DRUPAL_OPTIONAL);
+    $this->setCommentForm(TRUE);
+    $this->setCommentSubject(TRUE);
+    $this->setCommentSettings('default_mode', CommentManagerInterface::COMMENT_MODE_THREADED, 'Comment paging changed.');
+
+    // Log in as web user.
+    $this->drupalLogin($this->webUser);
+
+    // As the web user, fill in the comment form and preview the comment.
+    $edit = [];
+    $edit['subject[0][value]'] = $this->randomMachineName(8);
+    $edit['comment_body[0][value]'] = $this->randomMachineName(16);
+    $this->drupalGet('node/' . $this->node->id());
+    $this->submitForm($edit, 'Preview');
+
+    // Check that the preview is displaying the title and body.
+    $this->assertSession()->titleEquals('Preview comment | Drupal');
+    $this->assertSession()->pageTextContains($edit['subject[0][value]']);
+    $this->assertSession()->pageTextContains($edit['comment_body[0][value]']);
+
+    // Check that the title and body fields are displayed with the correct values.
+    $this->assertSession()->fieldValueEquals('subject[0][value]', $edit['subject[0][value]']);
+    $this->assertSession()->fieldValueEquals('comment_body[0][value]', $edit['comment_body[0][value]']);
+
+    // Store the content of this page.
+    $this->submitForm([], 'Save');
+    $this->assertSession()->pageTextContains('Your comment has been posted.');
+    $this->assertSession()->elementsCount('xpath', '//section[contains(@class, "comments")]/article', 1);
+
+    // Go back and re-submit the form.
+    $this->getSession()->getDriver()->back();
+    $submit_button = $this->assertSession()->buttonExists('Save');
+    $submit_button->click();
+    $this->assertSession()->pageTextContains('Your comment has been posted.');
+    $this->assertSession()->elementsCount('xpath', '//section[contains(@class, "comments")]/article', 2);
+  }
+
+  /**
+   * Tests comment edit, preview, and save.
+   */
+  public function testCommentEditPreviewSave(): void {
+    $web_user = $this->drupalCreateUser([
+      'access comments',
+      'post comments',
+      'skip comment approval',
+      'edit own comments',
+    ]);
+    $this->drupalLogin($this->adminUser);
+    $this->setCommentPreview(DRUPAL_OPTIONAL);
+    $this->setCommentForm(TRUE);
+    $this->setCommentSubject(TRUE);
+    $this->setCommentSettings('default_mode', CommentManagerInterface::COMMENT_MODE_THREADED, 'Comment paging changed.');
+
+    $edit = [];
+    $date = new DrupalDateTime('2008-03-02 17:23');
+    $edit['subject[0][value]'] = $this->randomMachineName(8);
+    $edit['comment_body[0][value]'] = $this->randomMachineName(16);
+    $edit['uid'] = $web_user->getAccountName() . ' (' . $web_user->id() . ')';
+    $edit['date[date]'] = $date->format('Y-m-d');
+    $edit['date[time]'] = $date->format('H:i:s');
+    $raw_date = $date->getTimestamp();
+    $expected_text_date = $this->container->get('date.formatter')->formatInterval(\Drupal::time()->getRequestTime() - $raw_date);
+    $expected_form_date = $date->format('Y-m-d');
+    $expected_form_time = $date->format('H:i:s');
+    $comment = $this->postComment($this->node, $edit['subject[0][value]'], $edit['comment_body[0][value]'], TRUE);
+    $this->drupalGet('comment/' . $comment->id() . '/edit');
+    $this->submitForm($edit, 'Preview');
+
+    // Check that the preview is displaying the subject, comment, author and date correctly.
+    $this->assertSession()->titleEquals('Preview comment | Drupal');
+    $this->assertSession()->pageTextContains($edit['subject[0][value]']);
+    $this->assertSession()->pageTextContains($edit['comment_body[0][value]']);
+    $this->assertSession()->pageTextContains($web_user->getAccountName());
+    $this->assertSession()->pageTextContains($expected_text_date);
+
+    // Check that the subject, comment, author and date fields are displayed with the correct values.
+    $this->assertSession()->fieldValueEquals('subject[0][value]', $edit['subject[0][value]']);
+    $this->assertSession()->fieldValueEquals('comment_body[0][value]', $edit['comment_body[0][value]']);
+    $this->assertSession()->fieldValueEquals('uid', $edit['uid']);
+    $this->assertSession()->fieldValueEquals('date[date]', $edit['date[date]']);
+    $this->assertSession()->fieldValueEquals('date[time]', $edit['date[time]']);
+
+    // Check that saving a comment produces a success message.
+    $this->drupalGet('comment/' . $comment->id() . '/edit');
+    $this->submitForm($edit, 'Save');
+    $this->assertSession()->pageTextContains('Your comment has been updated.');
+
+    // Check that the comment fields are correct after loading the saved comment.
+    $this->drupalGet('comment/' . $comment->id() . '/edit');
+    $this->assertSession()->fieldValueEquals('subject[0][value]', $edit['subject[0][value]']);
+    $this->assertSession()->fieldValueEquals('comment_body[0][value]', $edit['comment_body[0][value]']);
+    $this->assertSession()->fieldValueEquals('uid', $edit['uid']);
+    $this->assertSession()->fieldValueEquals('date[date]', $expected_form_date);
+    $this->assertSession()->fieldValueEquals('date[time]', $expected_form_time);
+
+    // Submit the form using the displayed values.
+    $displayed = [];
+    $displayed['subject[0][value]'] = $this->assertSession()->fieldExists('edit-subject-0-value')->getValue();
+    $displayed['comment_body[0][value]'] = $this->assertSession()->fieldExists('edit-comment-body-0-value')->getValue();
+    $displayed['uid'] = $this->assertSession()->fieldExists('edit-uid')->getValue();
+    $displayed['date[date]'] = $this->assertSession()->fieldExists('edit-date-date')->getValue();
+    $displayed['date[time]'] = $this->assertSession()->fieldExists('edit-date-time')->getValue();
+    $this->drupalGet('comment/' . $comment->id() . '/edit');
+    $this->submitForm($displayed, 'Save');
+
+    // Check that the saved comment is still correct.
+    $comment_storage = \Drupal::entityTypeManager()->getStorage('comment');
+    $comment_storage->resetCache([$comment->id()]);
+    /** @var \Drupal\comment\CommentInterface $comment_loaded */
+    $comment_loaded = Comment::load($comment->id());
+    $this->assertEquals($edit['subject[0][value]'], $comment_loaded->getSubject(), 'Subject loaded.');
+    $this->assertEquals($edit['comment_body[0][value]'], $comment_loaded->comment_body->value, 'Comment body loaded.');
+    $this->assertEquals($web_user->id(), $comment_loaded->getOwner()->id(), 'Name loaded.');
+    $this->assertEquals($raw_date, $comment_loaded->getCreatedTime(), 'Date loaded.');
+    $this->drupalLogout();
+
+    // Check that the date and time of the comment are correct when edited by
+    // non-admin users.
+    $user_edit = [];
+    $expected_created_time = $comment_loaded->getCreatedTime();
+    $this->drupalLogin($web_user);
+    // Web user cannot change the comment author.
+    unset($edit['uid']);
+    $this->drupalGet('comment/' . $comment->id() . '/edit');
+    $this->submitForm($user_edit, 'Save');
+    $comment_storage->resetCache([$comment->id()]);
+    $comment_loaded = Comment::load($comment->id());
+    $this->assertEquals($expected_created_time, $comment_loaded->getCreatedTime(), 'Expected date and time for comment edited.');
+    $this->drupalLogout();
+  }
+
+}

core/modules/comment/tests/src/Functional/CommentRssTest.php

@@ -0,0 +1,86 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+use Drupal\comment\Plugin\Field\FieldType\CommentItemInterface;
+use Drupal\Core\Cache\Cache;
+use Drupal\Core\Entity\Entity\EntityViewDisplay;
+use Drupal\Tests\system\Functional\Cache\AssertPageCacheContextsAndTagsTrait;
+
+/**
+ * Tests comments as part of an RSS feed.
+ *
+ * @group comment
+ */
+class CommentRssTest extends CommentTestBase {
+
+  use AssertPageCacheContextsAndTagsTrait;
+
+  /**
+   * Modules to install.
+   *
+   * @var array
+   */
+  protected static $modules = ['views'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // Setup the rss view display.
+    EntityViewDisplay::create([
+      'status' => TRUE,
+      'targetEntityType' => 'node',
+      'bundle' => 'article',
+      'mode' => 'rss',
+      'content' => ['links' => ['weight' => 100]],
+    ])->save();
+  }
+
+  /**
+   * Tests comments as part of an RSS feed.
+   */
+  public function testCommentRss(): void {
+    // Find comment in RSS feed.
+    $this->drupalLogin($this->webUser);
+    $this->postComment($this->node, $this->randomMachineName(), $this->randomMachineName());
+    $this->drupalGet('rss.xml');
+
+    $cache_contexts = [
+      'languages:language_interface',
+      'theme',
+      'url.site',
+      'user.node_grants:view',
+      'user.permissions',
+      'timezone',
+    ];
+    $this->assertCacheContexts($cache_contexts);
+
+    $cache_context_tags = \Drupal::service('cache_contexts_manager')->convertTokensToKeys($cache_contexts)->getCacheTags();
+    $this->assertCacheTags(Cache::mergeTags($cache_context_tags, [
+      'config:views.view.frontpage',
+      'node:1', 'node_list',
+      'node_view',
+      'user:3',
+    ]));
+
+    $raw = '<comments>' . $this->node->toUrl('canonical', ['fragment' => 'comments', 'absolute' => TRUE])->toString() . '</comments>';
+    $this->assertSession()->responseContains($raw);
+
+    // Hide comments from RSS feed and check presence.
+    $this->node->set('comment', CommentItemInterface::HIDDEN);
+    $this->node->save();
+    $this->drupalGet('rss.xml');
+    $this->assertSession()->responseNotContains($raw);
+  }
+
+}

core/modules/comment/tests/src/Functional/CommentStatisticsTest.php

@@ -0,0 +1,140 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+use Drupal\comment\CommentInterface;
+use Drupal\comment\CommentManagerInterface;
+use Drupal\comment\Entity\Comment;
+
+/**
+ * Tests comment statistics on nodes.
+ *
+ * @group comment
+ */
+class CommentStatisticsTest extends CommentTestBase {
+
+  /**
+   * A secondary user for posting comments.
+   *
+   * @var \Drupal\user\UserInterface
+   */
+  protected $webUser2;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // Add more permissions the admin user.
+    $this->adminUser->addRole($this->drupalCreateRole([
+      'administer permissions',
+      'access administration pages',
+      'administer site configuration',
+    ]))->save();
+    // Create a second user to post comments.
+    $this->webUser2 = $this->drupalCreateUser([
+      'post comments',
+      'create article content',
+      'edit own comments',
+      'skip comment approval',
+      'access comments',
+      'access content',
+    ]);
+  }
+
+  /**
+   * Tests the node comment statistics.
+   */
+  public function testCommentNodeCommentStatistics(): void {
+    $node_storage = $this->container->get('entity_type.manager')->getStorage('node');
+    // Set comments to have subject and preview disabled.
+    $this->setCommentPreview(DRUPAL_DISABLED);
+    $this->setCommentForm(TRUE);
+    $this->setCommentSubject(FALSE);
+    $this->setCommentSettings('default_mode', CommentManagerInterface::COMMENT_MODE_THREADED, 'Comment paging changed.');
+
+    // Checks the initial values of node comment statistics with no comment.
+    $node = $node_storage->load($this->node->id());
+    $this->assertEquals($this->node->getCreatedTime(), $node->get('comment')->last_comment_timestamp, 'The initial value of node last_comment_timestamp is the node created date.');
+    $this->assertNull($node->get('comment')->last_comment_name, 'The initial value of node last_comment_name is NULL.');
+    $this->assertEquals($this->webUser->id(), $node->get('comment')->last_comment_uid, 'The initial value of node last_comment_uid is the node uid.');
+    $this->assertEquals(0, $node->get('comment')->comment_count, 'The initial value of node comment_count is zero.');
+
+    // Post comment #1 as web_user2.
+    $this->drupalLogin($this->webUser2);
+    $comment_text = $this->randomMachineName();
+    $this->postComment($this->node, $comment_text);
+
+    // Checks the new values of node comment statistics with comment #1.
+    // The node cache needs to be reset before reload.
+    $node_storage->resetCache([$this->node->id()]);
+    $node = $node_storage->load($this->node->id());
+    $this->assertSame('', $node->get('comment')->last_comment_name, 'The value of node last_comment_name should be an empty string.');
+    $this->assertEquals($this->webUser2->id(), $node->get('comment')->last_comment_uid, 'The value of node last_comment_uid is the comment #1 uid.');
+    $this->assertEquals(1, $node->get('comment')->comment_count, 'The value of node comment_count is 1.');
+    $this->drupalLogout();
+
+    // Prepare for anonymous comment submission (comment approval enabled).
+    // Note we don't use user_role_change_permissions(), because that caused
+    // random test failures.
+    $this->drupalLogin($this->adminUser);
+
+    $this->drupalGet('admin/people/permissions');
+    $edit = [
+      'anonymous[access comments]' => 1,
+      'anonymous[post comments]' => 1,
+      'anonymous[skip comment approval]' => 0,
+    ];
+    $this->submitForm($edit, 'Save permissions');
+    $this->drupalLogout();
+
+    // Ensure that the poster can leave some contact info.
+    $this->setCommentAnonymous(CommentInterface::ANONYMOUS_MAY_CONTACT);
+
+    // Post comment #2 as anonymous (comment approval enabled).
+    $this->drupalGet('comment/reply/node/' . $this->node->id() . '/comment');
+    $anonymous_comment = $this->postComment($this->node, $this->randomMachineName(), '', TRUE);
+
+    // Checks the new values of node comment statistics with comment #2 and
+    // ensure they haven't changed since the comment has not been moderated.
+    // The node needs to be reloaded with the cache reset.
+    $node_storage->resetCache([$this->node->id()]);
+    $node = $node_storage->load($this->node->id());
+    $this->assertSame('', $node->get('comment')->last_comment_name, 'The value of node last_comment_name should be an empty string.');
+    $this->assertEquals($this->webUser2->id(), $node->get('comment')->last_comment_uid, 'The value of node last_comment_uid is still the comment #1 uid.');
+    $this->assertEquals(1, $node->get('comment')->comment_count, 'The value of node comment_count is still 1.');
+
+    // Prepare for anonymous comment submission (no approval required).
+    // Note we don't use user_role_change_permissions(), because that caused
+    // random test failures.
+    $this->drupalLogin($this->adminUser);
+    $this->drupalGet('admin/people/permissions');
+    $edit = [
+      'anonymous[skip comment approval]' => 1,
+    ];
+    $this->submitForm($edit, 'Save permissions');
+    $this->drupalLogout();
+
+    // Post comment #3 as anonymous.
+    $this->drupalGet('comment/reply/node/' . $this->node->id() . '/comment');
+    $anonymous_comment = $this->postComment($this->node, $this->randomMachineName(), '', ['name' => $this->randomMachineName()]);
+    $comment_loaded = Comment::load($anonymous_comment->id());
+
+    // Checks the new values of node comment statistics with comment #3.
+    // The node needs to be reloaded with the cache reset.
+    $node_storage->resetCache([$this->node->id()]);
+    $node = $node_storage->load($this->node->id());
+    $this->assertEquals($comment_loaded->getAuthorName(), $node->get('comment')->last_comment_name, 'The value of node last_comment_name is the name of the anonymous user.');
+    $this->assertEquals(0, $node->get('comment')->last_comment_uid, 'The value of node last_comment_uid is zero.');
+    $this->assertEquals(2, $node->get('comment')->comment_count, 'The value of node comment_count is 2.');
+  }
+
+}

core/modules/comment/tests/src/Functional/CommentStatusFieldAccessTest.php

@@ -0,0 +1,102 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+use Drupal\comment\Tests\CommentTestTrait;
+use Drupal\node\Entity\NodeType;
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests comment status field access.
+ *
+ * @group comment
+ */
+class CommentStatusFieldAccessTest extends BrowserTestBase {
+
+  use CommentTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  public $profile = 'testing';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Comment admin.
+   *
+   * @var \Drupal\user\UserInterface
+   */
+  protected $commentAdmin;
+
+  /**
+   * Node author.
+   *
+   * @var \Drupal\user\UserInterface
+   */
+  protected $nodeAuthor;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'node',
+    'comment',
+    'user',
+    'system',
+    'text',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $node_type = NodeType::create([
+      'type' => 'article',
+      'name' => 'Article',
+    ]);
+    $node_type->save();
+    $this->nodeAuthor = $this->drupalCreateUser([
+      'create article content',
+      'skip comment approval',
+      'post comments',
+      'edit own comments',
+      'access comments',
+      'administer nodes',
+    ]);
+    $this->commentAdmin = $this->drupalCreateUser([
+      'administer comments',
+      'create article content',
+      'edit own comments',
+      'skip comment approval',
+      'post comments',
+      'access comments',
+      'administer nodes',
+    ]);
+    $this->addDefaultCommentField('node', 'article');
+  }
+
+  /**
+   * Tests comment status field access.
+   */
+  public function testCommentStatusFieldAccessStatus(): void {
+    $this->drupalLogin($this->nodeAuthor);
+    $this->drupalGet('node/add/article');
+    $assert = $this->assertSession();
+    $assert->fieldNotExists('comment[0][status]');
+    $this->submitForm(['title[0][value]' => 'Node 1'], 'Save');
+    $assert->fieldExists('subject[0][value]');
+    $this->drupalLogin($this->commentAdmin);
+    $this->drupalGet('node/add/article');
+    $assert->fieldExists('comment[0][status]');
+    $this->submitForm(['title[0][value]' => 'Node 2'], 'Save');
+    $assert->fieldExists('subject[0][value]');
+  }
+
+}

core/modules/comment/tests/src/Functional/CommentTestBase.php

@@ -0,0 +1,418 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+use Drupal\Component\Render\FormattableMarkup;
+use Drupal\comment\Entity\CommentType;
+use Drupal\comment\Entity\Comment;
+use Drupal\comment\CommentInterface;
+use Drupal\comment\Tests\CommentTestTrait;
+use Drupal\field\Entity\FieldConfig;
+use Drupal\comment\Plugin\Field\FieldType\CommentItemInterface;
+use Drupal\node\Entity\NodeType;
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Provides setup and helper methods for comment tests.
+ */
+abstract class CommentTestBase extends BrowserTestBase {
+
+  use CommentTestTrait;
+
+  /**
+   * Modules to install.
+   *
+   * @var array
+   */
+  protected static $modules = [
+    'block',
+    'comment',
+    'node',
+    'history',
+    'field_ui',
+    'datetime',
+  ];
+
+  /**
+   * An administrative user with permission to configure comment settings.
+   *
+   * @var \Drupal\user\UserInterface
+   */
+  protected $adminUser;
+
+  /**
+   * A normal user with permission to post comments.
+   *
+   * @var \Drupal\user\UserInterface
+   */
+  protected $webUser;
+
+  /**
+   * A test node to which comments will be posted.
+   *
+   * @var \Drupal\node\NodeInterface
+   */
+  protected $node;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // Create an article content type only if it does not yet exist, so that
+    // child classes may specify the standard profile.
+    $types = NodeType::loadMultiple();
+    if (empty($types['article'])) {
+      $this->drupalCreateContentType(['type' => 'article', 'name' => t('Article')]);
+    }
+
+    // Create two test users.
+    $this->adminUser = $this->drupalCreateUser([
+      'administer content types',
+      'administer comments',
+      'administer comment types',
+      'administer comment fields',
+      'administer comment display',
+      'skip comment approval',
+      'post comments',
+      'access comments',
+      // Usernames aren't shown in comment edit form autocomplete unless this
+      // permission is granted.
+      'access user profiles',
+      'access content',
+    ]);
+    $this->webUser = $this->drupalCreateUser([
+      'access comments',
+      'post comments',
+      'create article content',
+      'edit own comments',
+      'skip comment approval',
+      'access content',
+    ]);
+
+    // Create comment field on article.
+    $this->addDefaultCommentField('node', 'article');
+
+    // Create a test node authored by the web user.
+    $this->node = $this->drupalCreateNode(['type' => 'article', 'promote' => 1, 'uid' => $this->webUser->id()]);
+    $this->drupalPlaceBlock('local_tasks_block');
+  }
+
+  /**
+   * Posts a comment.
+   *
+   * @param \Drupal\Core\Entity\EntityInterface|null $entity
+   *   Node to post comment on or NULL to post to the previously loaded page.
+   * @param string $comment
+   *   Comment body.
+   * @param string $subject
+   *   Comment subject.
+   * @param string $contact
+   *   Set to NULL for no contact info, TRUE to ignore success checking, and
+   *   array of values to set contact info.
+   * @param string $field_name
+   *   (optional) Field name through which the comment should be posted.
+   *   Defaults to 'comment'.
+   *
+   * @return \Drupal\comment\CommentInterface|null
+   *   The posted comment or NULL when posted comment was not found.
+   */
+  public function postComment($entity, $comment, $subject = '', $contact = NULL, $field_name = 'comment') {
+    $edit = [];
+    $edit['comment_body[0][value]'] = $comment;
+
+    if ($entity !== NULL) {
+      $field = FieldConfig::loadByName($entity->getEntityTypeId(), $entity->bundle(), $field_name);
+    }
+    else {
+      $field = FieldConfig::loadByName('node', 'article', $field_name);
+    }
+    $preview_mode = $field->getSetting('preview');
+
+    // Must get the page before we test for fields.
+    if ($entity !== NULL) {
+      $this->drupalGet('comment/reply/' . $entity->getEntityTypeId() . '/' . $entity->id() . '/' . $field_name);
+    }
+
+    // Determine the visibility of subject form field.
+    $display_repository = $this->container->get('entity_display.repository');
+    if ($display_repository->getFormDisplay('comment', 'comment')->getComponent('subject')) {
+      // Subject input allowed.
+      $edit['subject[0][value]'] = $subject;
+    }
+    else {
+      $this->assertSession()->fieldNotExists('subject[0][value]');
+    }
+
+    if ($contact !== NULL && is_array($contact)) {
+      $edit += $contact;
+    }
+    switch ($preview_mode) {
+      case DRUPAL_REQUIRED:
+        // Preview required so no save button should be found.
+        $this->assertSession()->buttonNotExists('Save');
+        $this->submitForm($edit, 'Preview');
+        // Don't break here so that we can test post-preview field presence and
+        // function below.
+      case DRUPAL_OPTIONAL:
+        $this->assertSession()->buttonExists('Preview');
+        $this->assertSession()->buttonExists('Save');
+        $this->submitForm($edit, 'Save');
+        break;
+
+      case DRUPAL_DISABLED:
+        $this->assertSession()->buttonNotExists('Preview');
+        $this->assertSession()->buttonExists('Save');
+        $this->submitForm($edit, 'Save');
+        break;
+    }
+    $match = [];
+    // Get comment ID
+    preg_match('/#comment-([0-9]+)/', $this->getURL(), $match);
+
+    // Get comment.
+    if ($contact !== TRUE) {
+      // If true then attempting to find error message.
+      if ($subject) {
+        $this->assertSession()->pageTextContains($subject);
+      }
+      $this->assertSession()->pageTextContains($comment);
+      // Check the comment ID was extracted.
+      $this->assertArrayHasKey(1, $match);
+    }
+
+    if (isset($match[1])) {
+      \Drupal::entityTypeManager()->getStorage('comment')->resetCache([$match[1]]);
+      return Comment::load($match[1]);
+    }
+  }
+
+  /**
+   * Checks current page for specified comment.
+   *
+   * @param \Drupal\comment\CommentInterface $comment
+   *   The comment object.
+   * @param bool $reply
+   *   Boolean indicating whether the comment is a reply to another comment.
+   *
+   * @return bool
+   *   Boolean indicating whether the comment was found.
+   */
+  public function commentExists(?CommentInterface $comment = NULL, $reply = FALSE) {
+    if ($comment) {
+      $comment_element = $this->cssSelect(($reply ? '.indented ' : '') . 'article#comment-' . $comment->id());
+      if (empty($comment_element)) {
+        return FALSE;
+      }
+
+      $comment_title = $comment_element[0]->find('xpath', 'div/h3/a');
+      if (empty($comment_title) || $comment_title->getText() !== $comment->getSubject()) {
+        return FALSE;
+      }
+
+      $comment_body = $comment_element[0]->find('xpath', 'div/div/p');
+      if (empty($comment_body) || $comment_body->getText() !== $comment->comment_body->value) {
+        return FALSE;
+      }
+
+      return TRUE;
+    }
+    else {
+      return FALSE;
+    }
+  }
+
+  /**
+   * Deletes a comment.
+   *
+   * @param \Drupal\comment\CommentInterface $comment
+   *   Comment to delete.
+   */
+  public function deleteComment(CommentInterface $comment) {
+    $this->drupalGet('comment/' . $comment->id() . '/delete');
+    $this->submitForm([], 'Delete');
+    $this->assertSession()->pageTextContains('The comment and all its replies have been deleted.');
+  }
+
+  /**
+   * Sets the value governing whether the subject field should be enabled.
+   *
+   * @param bool $enabled
+   *   Boolean specifying whether the subject field should be enabled.
+   */
+  public function setCommentSubject($enabled) {
+    $form_display = $this->container->get('entity_display.repository')
+      ->getFormDisplay('comment', 'comment');
+
+    if ($enabled) {
+      $form_display->setComponent('subject', [
+        'type' => 'string_textfield',
+      ]);
+    }
+    else {
+      $form_display->removeComponent('subject');
+    }
+    $form_display->save();
+  }
+
+  /**
+   * Sets the value governing the previewing mode for the comment form.
+   *
+   * @param int $mode
+   *   The preview mode: DRUPAL_DISABLED, DRUPAL_OPTIONAL or DRUPAL_REQUIRED.
+   * @param string $field_name
+   *   (optional) Field name through which the comment should be posted.
+   *   Defaults to 'comment'.
+   */
+  public function setCommentPreview($mode, $field_name = 'comment') {
+    switch ($mode) {
+      case DRUPAL_DISABLED:
+        $mode_text = 'disabled';
+        break;
+
+      case DRUPAL_OPTIONAL:
+        $mode_text = 'optional';
+        break;
+
+      case DRUPAL_REQUIRED:
+        $mode_text = 'required';
+        break;
+    }
+    $this->setCommentSettings('preview', $mode, new FormattableMarkup('Comment preview @mode_text.', ['@mode_text' => $mode_text]), $field_name);
+  }
+
+  /**
+   * Sets the value governing whether the comment form is on its own page.
+   *
+   * @param bool $enabled
+   *   TRUE if the comment form should be displayed on the same page as the
+   *   comments; FALSE if it should be displayed on its own page.
+   * @param string $field_name
+   *   (optional) Field name through which the comment should be posted.
+   *   Defaults to 'comment'.
+   */
+  public function setCommentForm($enabled, $field_name = 'comment') {
+    $this->setCommentSettings('form_location', ($enabled ? CommentItemInterface::FORM_BELOW : CommentItemInterface::FORM_SEPARATE_PAGE), 'Comment controls ' . ($enabled ? 'enabled' : 'disabled') . '.', $field_name);
+  }
+
+  /**
+   * Sets the value governing restrictions on anonymous comments.
+   *
+   * @param int $level
+   *   The level of the contact information allowed for anonymous comments:
+   *   - 0: No contact information allowed.
+   *   - 1: Contact information allowed but not required.
+   *   - 2: Contact information required.
+   */
+  public function setCommentAnonymous($level) {
+    $this->setCommentSettings('anonymous', $level, new FormattableMarkup('Anonymous commenting set to level @level.', ['@level' => $level]));
+  }
+
+  /**
+   * Sets the value specifying the default number of comments per page.
+   *
+   * @param int $number
+   *   Comments per page value.
+   * @param string $field_name
+   *   (optional) Field name through which the comment should be posted.
+   *   Defaults to 'comment'.
+   */
+  public function setCommentsPerPage($number, $field_name = 'comment') {
+    $this->setCommentSettings('per_page', $number, new FormattableMarkup('Number of comments per page set to @number.', ['@number' => $number]), $field_name);
+  }
+
+  /**
+   * Sets a comment settings variable for the article content type.
+   *
+   * @param string $name
+   *   Name of variable.
+   * @param string $value
+   *   Value of variable.
+   * @param string $message
+   *   Status message to display.
+   * @param string $field_name
+   *   (optional) Field name through which the comment should be posted.
+   *   Defaults to 'comment'.
+   */
+  public function setCommentSettings($name, $value, $message, $field_name = 'comment') {
+    $field = FieldConfig::loadByName('node', 'article', $field_name);
+    $field->setSetting($name, $value);
+    $field->save();
+  }
+
+  /**
+   * Checks whether the commenter's contact information is displayed.
+   *
+   * @return bool
+   *   Contact info is available.
+   */
+  public function commentContactInfoAvailable() {
+    return (bool) preg_match('/(input).*?(name="name").*?(input).*?(name="mail").*?(input).*?(name="homepage")/s', $this->getSession()->getPage()->getContent());
+  }
+
+  /**
+   * Performs the specified operation on the specified comment.
+   *
+   * @param \Drupal\comment\CommentInterface $comment
+   *   Comment to perform operation on.
+   * @param string $operation
+   *   Operation to perform.
+   * @param bool $approval
+   *   Operation is found on approval page.
+   */
+  public function performCommentOperation(CommentInterface $comment, $operation, $approval = FALSE) {
+    $edit = [];
+    $edit['operation'] = $operation;
+    $edit['comments[' . $comment->id() . ']'] = TRUE;
+    $this->drupalGet('admin/content/comment' . ($approval ? '/approval' : ''));
+    $this->submitForm($edit, 'Update');
+
+    if ($operation == 'delete') {
+      $this->submitForm([], 'Delete');
+      $this->assertSession()->pageTextContains('Deleted 1 comment.');
+    }
+    else {
+      $this->assertSession()->pageTextContains('The update has been performed.');
+    }
+  }
+
+  /**
+   * Gets the comment ID for an unapproved comment.
+   *
+   * @param string $subject
+   *   Comment subject to find.
+   *
+   * @return int
+   *   Comment id.
+   */
+  public function getUnapprovedComment($subject) {
+    $this->drupalGet('admin/content/comment/approval');
+    preg_match('/href="(.*?)#comment-([^"]+)"(.*?)>(' . $subject . ')/', $this->getSession()->getPage()->getContent(), $match);
+
+    return $match[2];
+  }
+
+  /**
+   * Creates a comment type (bundle).
+   *
+   * @param string $label
+   *   The comment type label.
+   *
+   * @return \Drupal\comment\Entity\CommentType
+   *   Created comment type.
+   */
+  protected function createCommentType($label) {
+    $bundle = CommentType::create([
+      'id' => $label,
+      'label' => $label,
+      'description' => '',
+      'target_entity_type_id' => 'node',
+    ]);
+    $bundle->save();
+    return $bundle;
+  }
+
+}

core/modules/comment/tests/src/Functional/CommentThreadingTest.php

@@ -0,0 +1,172 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+use Drupal\comment\CommentManagerInterface;
+
+/**
+ * Tests to make sure the comment number increments properly.
+ *
+ * @group comment
+ */
+class CommentThreadingTest extends CommentTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Tests the comment threading.
+   */
+  public function testCommentThreading(): void {
+    // Set comments to have a subject with preview disabled.
+    $this->setCommentPreview(DRUPAL_DISABLED);
+    $this->setCommentForm(TRUE);
+    $this->setCommentSubject(TRUE);
+    $this->setCommentSettings('default_mode', CommentManagerInterface::COMMENT_MODE_THREADED, 'Comment paging changed.');
+
+    // Create a node.
+    $this->drupalLogin($this->webUser);
+    $this->node = $this->drupalCreateNode(['type' => 'article', 'promote' => 1, 'uid' => $this->webUser->id()]);
+
+    // Post comment #1.
+    $this->drupalLogin($this->webUser);
+    $subject_text = $this->randomMachineName();
+    $comment_text = $this->randomMachineName();
+
+    $comment1 = $this->postComment($this->node, $comment_text, $subject_text, TRUE);
+    // Confirm that the comment was created and has the correct threading.
+    $this->assertTrue($this->commentExists($comment1), 'Comment #1. Comment found.');
+    $this->assertEquals('01/', $comment1->getThread());
+    // Confirm that there is no reference to a parent comment.
+    $this->assertNoParentLink($comment1->id());
+
+    // Post comment #2 following the comment #1 to test if it correctly jumps
+    // out the indentation in case there is a thread above.
+    $subject_text = $this->randomMachineName();
+    $comment_text = $this->randomMachineName();
+    $this->postComment($this->node, $comment_text, $subject_text, TRUE);
+
+    // Reply to comment #1 creating comment #1_3.
+    $this->drupalGet('comment/reply/node/' . $this->node->id() . '/comment/' . $comment1->id());
+    $comment1_3 = $this->postComment(NULL, $this->randomMachineName(), '', TRUE);
+
+    // Confirm that the comment was created and has the correct threading.
+    $this->assertTrue($this->commentExists($comment1_3, TRUE), 'Comment #1_3. Reply found.');
+    $this->assertEquals('01.00/', $comment1_3->getThread());
+    // Confirm that there is a link to the parent comment.
+    $this->assertParentLink($comment1_3->id(), $comment1->id());
+
+    // Reply to comment #1_3 creating comment #1_3_4.
+    $this->drupalGet('comment/reply/node/' . $this->node->id() . '/comment/' . $comment1_3->id());
+    $comment1_3_4 = $this->postComment(NULL, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+
+    // Confirm that the comment was created and has the correct threading.
+    $this->assertTrue($this->commentExists($comment1_3_4, TRUE), 'Comment #1_3_4. Second reply found.');
+    $this->assertEquals('01.00.00/', $comment1_3_4->getThread());
+    // Confirm that there is a link to the parent comment.
+    $this->assertParentLink($comment1_3_4->id(), $comment1_3->id());
+
+    // Reply to comment #1 creating comment #1_5.
+    $this->drupalGet('comment/reply/node/' . $this->node->id() . '/comment/' . $comment1->id());
+
+    $comment1_5 = $this->postComment(NULL, $this->randomMachineName(), '', TRUE);
+
+    // Confirm that the comment was created and has the correct threading.
+    $this->assertTrue($this->commentExists($comment1_5), 'Comment #1_5. Third reply found.');
+    $this->assertEquals('01.01/', $comment1_5->getThread());
+    // Confirm that there is a link to the parent comment.
+    $this->assertParentLink($comment1_5->id(), $comment1->id());
+
+    // Post comment #3 overall comment #5.
+    $this->drupalLogin($this->webUser);
+    $subject_text = $this->randomMachineName();
+    $comment_text = $this->randomMachineName();
+
+    $comment5 = $this->postComment($this->node, $comment_text, $subject_text, TRUE);
+    // Confirm that the comment was created and has the correct threading.
+    $this->assertTrue($this->commentExists($comment5), 'Comment #5. Second comment found.');
+    $this->assertEquals('03/', $comment5->getThread());
+    // Confirm that there is no link to a parent comment.
+    $this->assertNoParentLink($comment5->id());
+
+    // Reply to comment #5 creating comment #5_6.
+    $this->drupalGet('comment/reply/node/' . $this->node->id() . '/comment/' . $comment5->id());
+    $comment5_6 = $this->postComment(NULL, $this->randomMachineName(), '', TRUE);
+
+    // Confirm that the comment was created and has the correct threading.
+    $this->assertTrue($this->commentExists($comment5_6, TRUE), 'Comment #6. Reply found.');
+    $this->assertEquals('03.00/', $comment5_6->getThread());
+    // Confirm that there is a link to the parent comment.
+    $this->assertParentLink($comment5_6->id(), $comment5->id());
+
+    // Reply to comment #5_6 creating comment #5_6_7.
+    $this->drupalGet('comment/reply/node/' . $this->node->id() . '/comment/' . $comment5_6->id());
+    $comment5_6_7 = $this->postComment(NULL, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+
+    // Confirm that the comment was created and has the correct threading.
+    $this->assertTrue($this->commentExists($comment5_6_7, TRUE), 'Comment #5_6_7. Second reply found.');
+    $this->assertEquals('03.00.00/', $comment5_6_7->getThread());
+    // Confirm that there is a link to the parent comment.
+    $this->assertParentLink($comment5_6_7->id(), $comment5_6->id());
+
+    // Reply to comment #5 creating comment #5_8.
+    $this->drupalGet('comment/reply/node/' . $this->node->id() . '/comment/' . $comment5->id());
+    $comment5_8 = $this->postComment(NULL, $this->randomMachineName(), '', TRUE);
+
+    // Confirm that the comment was created and has the correct threading.
+    $this->assertTrue($this->commentExists($comment5_8), 'Comment #5_8. Third reply found.');
+    $this->assertEquals('03.01/', $comment5_8->getThread());
+    // Confirm that there is a link to the parent comment.
+    $this->assertParentLink($comment5_8->id(), $comment5->id());
+  }
+
+  /**
+   * Asserts that the link to the specified parent comment is present.
+   *
+   * @param string $cid
+   *   The comment ID to check.
+   * @param string $pid
+   *   The expected parent comment ID.
+   *
+   * @internal
+   */
+  protected function assertParentLink(string $cid, string $pid): void {
+    // This pattern matches a markup structure like:
+    // @code
+    // <article id="comment-2">
+    //   <p>
+    //     In reply to
+    //     <a href="...comment-1"></a>
+    //   </p>
+    // </article>
+    // @endcode
+    $pattern = "//article[@id='comment-$cid']//p/a[contains(@href, 'comment-$pid')]";
+
+    $this->assertSession()->elementExists('xpath', $pattern);
+
+    // A parent link is always accompanied by the text "In reply to".
+    // If we don't assert this text here, then the assertNoParentLink()
+    // method is not effective.
+    $pattern = "//article[@id='comment-$cid']";
+    $this->assertSession()->elementTextContains('xpath', $pattern, 'In reply to');
+  }
+
+  /**
+   * Asserts that the specified comment does not have a link to a parent.
+   *
+   * @param string $cid
+   *   The comment ID to check.
+   *
+   * @internal
+   */
+  protected function assertNoParentLink(string $cid): void {
+    $pattern = "//article[@id='comment-$cid']";
+    // A parent link is always accompanied by the text "In reply to".
+    $this->assertSession()->elementTextNotContains('xpath', $pattern, 'In reply to');
+  }
+
+}

core/modules/comment/tests/src/Functional/CommentTitleTest.php

@@ -0,0 +1,102 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+/**
+ * Tests that appropriate and accessible markup is created for comment titles.
+ *
+ * @group comment
+ */
+class CommentTitleTest extends CommentTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Tests markup for comments with empty titles.
+   */
+  public function testCommentEmptyTitles(): void {
+    // Create a node.
+    $this->drupalLogin($this->webUser);
+    $this->node = $this->drupalCreateNode(['type' => 'article', 'promote' => 1, 'uid' => $this->webUser->id()]);
+
+    // Post comment #1 and verify that h3 is rendered.
+    $subject_text = "Test subject";
+    $comment_text = "Test comment";
+    $this->postComment($this->node, $comment_text, $subject_text, TRUE);
+    // Tests that markup is generated for the comment title.
+    $regex_h3 = '|<h3[^>]*>.*?</h3>|';
+    $this->assertSession()->responseMatches($regex_h3);
+
+    // Installs module that sets comment title to an empty string.
+    \Drupal::service('module_installer')->install(['comment_empty_title_test']);
+
+    // Set comments to have a subject with preview disabled.
+    $this->setCommentPreview(DRUPAL_DISABLED);
+    $this->setCommentForm(TRUE);
+    $this->setCommentSubject(TRUE);
+
+    // Create a new node.
+    $this->node = $this->drupalCreateNode(['type' => 'article', 'promote' => 1, 'uid' => $this->webUser->id()]);
+
+    // Post another comment and verify that h3 is not rendered.
+    $subject_text = $this->randomMachineName();
+    $comment_text = $this->randomMachineName();
+    $comment = $this->postComment($this->node, $comment_text, $subject_text, TRUE);
+
+    // The entity fields for name and mail have no meaning if the user is not
+    // Anonymous.
+    $this->assertNull($comment->name->value);
+    $this->assertNull($comment->mail->value);
+
+    // Confirm that the comment was created.
+    $regex = '/<article(.*?)id="comment-' . $comment->id() . '"(.*?)';
+    $regex .= $comment->comment_body->value . '(.*?)';
+    $regex .= '/s';
+    // Verify that the comment is created successfully.
+    $this->assertSession()->responseMatches($regex);
+    // Tests that markup is not generated for the comment title.
+    $this->assertSession()->responseNotMatches($regex_h3);
+    $this->assertSession()->pageTextNotContains($subject_text);
+  }
+
+  /**
+   * Tests markup for comments with populated titles.
+   */
+  public function testCommentPopulatedTitles(): void {
+    // Set comments to have a subject with preview disabled.
+    $this->setCommentPreview(DRUPAL_DISABLED);
+    $this->setCommentForm(TRUE);
+    $this->setCommentSubject(TRUE);
+
+    // Create a node.
+    $this->drupalLogin($this->webUser);
+    $this->node = $this->drupalCreateNode(['type' => 'article', 'promote' => 1, 'uid' => $this->webUser->id()]);
+
+    // Post comment #1 and verify that title is rendered in h3.
+    $subject_text = $this->randomMachineName();
+    $comment_text = $this->randomMachineName();
+    $comment1 = $this->postComment($this->node, $comment_text, $subject_text, TRUE);
+
+    // The entity fields for name and mail have no meaning if the user is not
+    // Anonymous.
+    $this->assertNull($comment1->name->value);
+    $this->assertNull($comment1->mail->value);
+
+    // Confirm that the comment was created.
+    $this->assertTrue($this->commentExists($comment1), 'Comment #1. Comment found.');
+    // Tests that markup is created for comment with heading.
+    $this->assertSession()->responseMatches('|<h3[^>]*><a[^>]*>' . $subject_text . '</a></h3>|');
+    // Tests that the comment's title link is the permalink of the comment.
+    $comment_permalink = $this->cssSelect('.permalink');
+    $comment_permalink = $comment_permalink[0]->getAttribute('href');
+    // Tests that the comment's title link contains the URL fragment.
+    $this->assertStringContainsString('#comment-' . $comment1->id(), $comment_permalink, "The comment's title link contains the url fragment.");
+    $this->assertEquals($comment1->permalink()->toString(), $comment_permalink, "The comment's title has the correct link.");
+  }
+
+}

core/modules/comment/tests/src/Functional/CommentTokenReplaceTest.php

@@ -0,0 +1,193 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+use Drupal\comment\Plugin\Field\FieldType\CommentItemInterface;
+use Drupal\Component\Utility\Html;
+use Drupal\Component\Utility\UrlHelper;
+use Drupal\comment\Entity\Comment;
+use Drupal\Core\Render\BubbleableMetadata;
+use Drupal\node\Entity\Node;
+use Drupal\taxonomy\Entity\Term;
+use Drupal\taxonomy\Entity\Vocabulary;
+use Drupal\user\Entity\User;
+
+/**
+ * Tests comment token replacement.
+ *
+ * @group comment
+ */
+class CommentTokenReplaceTest extends CommentTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['taxonomy'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Creates a comment, then tests the tokens generated from it.
+   */
+  public function testCommentTokenReplacement(): void {
+    $token_service = \Drupal::token();
+    $language_interface = \Drupal::languageManager()->getCurrentLanguage();
+    $url_options = [
+      'absolute' => TRUE,
+      'language' => $language_interface,
+    ];
+
+    // Setup vocabulary.
+    Vocabulary::create([
+      'vid' => 'tags',
+      'name' => 'Tags',
+    ])->save();
+
+    // Change the title of the admin user.
+    $this->adminUser->name->value = 'This is a title with some special & > " stuff.';
+    $this->adminUser->save();
+    $this->drupalLogin($this->adminUser);
+
+    // Set comment variables.
+    $this->setCommentSubject(TRUE);
+
+    // To test hostname token field should be populated.
+    \Drupal::configFactory()
+      ->getEditable('comment.settings')
+      ->set('log_ip_addresses', TRUE)
+      ->save(TRUE);
+
+    // Create a node and a comment.
+    $node = $this->drupalCreateNode(['type' => 'article', 'title' => '<script>alert("123")</script>']);
+    $parent_comment = $this->postComment($node, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+
+    // Post a reply to the comment.
+    $this->drupalGet('comment/reply/node/' . $node->id() . '/comment/' . $parent_comment->id());
+    $child_comment = $this->postComment(NULL, $this->randomMachineName(), $this->randomMachineName());
+    $comment = Comment::load($child_comment->id());
+    $comment->setHomepage('http://example.org/');
+
+    // Add HTML to ensure that sanitation of some fields tested directly.
+    $comment->setSubject('<blink>Blinking Comment</blink>');
+
+    // Generate and test tokens.
+    $tests = [];
+    $tests['[comment:cid]'] = $comment->id();
+    $tests['[comment:hostname]'] = $comment->getHostname();
+    $tests['[comment:author]'] = Html::escape($comment->getAuthorName());
+    $tests['[comment:mail]'] = $this->adminUser->getEmail();
+    $tests['[comment:homepage]'] = UrlHelper::filterBadProtocol($comment->getHomepage());
+    $tests['[comment:title]'] = Html::escape($comment->getSubject());
+    $tests['[comment:body]'] = $comment->comment_body->processed;
+    $tests['[comment:langcode]'] = $comment->language()->getId();
+    $tests['[comment:url]'] = $comment->toUrl('canonical', $url_options + ['fragment' => 'comment-' . $comment->id()])->toString();
+    $tests['[comment:edit-url]'] = $comment->toUrl('edit-form', $url_options)->toString();
+    $tests['[comment:created]'] = \Drupal::service('date.formatter')->format($comment->getCreatedTime(), 'medium', ['langcode' => $language_interface->getId()]);
+    $tests['[comment:created:since]'] = \Drupal::service('date.formatter')->formatTimeDiffSince($comment->getCreatedTime(), ['langcode' => $language_interface->getId()]);
+    $tests['[comment:changed:since]'] = \Drupal::service('date.formatter')->formatTimeDiffSince($comment->getChangedTimeAcrossTranslations(), ['langcode' => $language_interface->getId()]);
+    $tests['[comment:parent:cid]'] = $comment->hasParentComment() ? $comment->getParentComment()->id() : NULL;
+    $tests['[comment:parent:title]'] = $parent_comment->getSubject();
+    $tests['[comment:entity]'] = Html::escape($node->getTitle());
+    // Test node specific tokens.
+    $tests['[comment:entity:nid]'] = $comment->getCommentedEntityId();
+    $tests['[comment:entity:title]'] = Html::escape($node->getTitle());
+    $tests['[comment:author:uid]'] = $comment->getOwnerId();
+    $tests['[comment:author:name]'] = Html::escape($this->adminUser->getDisplayName());
+
+    $base_bubbleable_metadata = BubbleableMetadata::createFromObject($comment);
+    $metadata_tests = [];
+    $metadata_tests['[comment:cid]'] = $base_bubbleable_metadata;
+    $metadata_tests['[comment:hostname]'] = $base_bubbleable_metadata;
+    $bubbleable_metadata = clone $base_bubbleable_metadata;
+    $bubbleable_metadata->addCacheableDependency($this->adminUser);
+    $metadata_tests['[comment:author]'] = $bubbleable_metadata;
+    $bubbleable_metadata = clone $base_bubbleable_metadata;
+    $bubbleable_metadata->addCacheableDependency($this->adminUser);
+    $metadata_tests['[comment:mail]'] = $bubbleable_metadata;
+    $metadata_tests['[comment:homepage]'] = $base_bubbleable_metadata;
+    $metadata_tests['[comment:title]'] = $base_bubbleable_metadata;
+    $metadata_tests['[comment:body]'] = $base_bubbleable_metadata;
+    $metadata_tests['[comment:langcode]'] = $base_bubbleable_metadata;
+    $metadata_tests['[comment:url]'] = $base_bubbleable_metadata;
+    $metadata_tests['[comment:edit-url]'] = $base_bubbleable_metadata;
+    $bubbleable_metadata = clone $base_bubbleable_metadata;
+    $metadata_tests['[comment:created]'] = $bubbleable_metadata->addCacheTags(['rendered']);
+    $bubbleable_metadata = clone $base_bubbleable_metadata;
+    $metadata_tests['[comment:created:since]'] = $bubbleable_metadata->setCacheMaxAge(0);
+    $bubbleable_metadata = clone $base_bubbleable_metadata;
+    $metadata_tests['[comment:changed:since]'] = $bubbleable_metadata->setCacheMaxAge(0);
+    $bubbleable_metadata = clone $base_bubbleable_metadata;
+    $metadata_tests['[comment:parent:cid]'] = $bubbleable_metadata->addCacheTags(['comment:1']);
+    $metadata_tests['[comment:parent:title]'] = $bubbleable_metadata;
+    $bubbleable_metadata = clone $base_bubbleable_metadata;
+    $metadata_tests['[comment:entity]'] = $bubbleable_metadata->addCacheTags(['node:2']);
+    // Test node specific tokens.
+    $metadata_tests['[comment:entity:nid]'] = $bubbleable_metadata;
+    $metadata_tests['[comment:entity:title]'] = $bubbleable_metadata;
+    $bubbleable_metadata = clone $base_bubbleable_metadata;
+    $metadata_tests['[comment:author:uid]'] = $bubbleable_metadata->addCacheTags(['user:2']);
+    $metadata_tests['[comment:author:name]'] = $bubbleable_metadata;
+
+    // Test to make sure that we generated something for each token.
+    $this->assertNotContains(0, array_map('strlen', $tests), 'No empty tokens generated.');
+
+    foreach ($tests as $input => $expected) {
+      $bubbleable_metadata = new BubbleableMetadata();
+      $output = $token_service->replace($input, ['comment' => $comment], ['langcode' => $language_interface->getId()], $bubbleable_metadata);
+      $this->assertSame((string) $expected, (string) $output, "Failed test case: {$input}");
+      $this->assertEquals($metadata_tests[$input], $bubbleable_metadata);
+    }
+
+    // Test anonymous comment author.
+    $author_name = 'This is a random & " > string';
+    $comment->setOwnerId(0)->setAuthorName($author_name);
+    $input = '[comment:author]';
+    $output = $token_service->replace($input, ['comment' => $comment], ['langcode' => $language_interface->getId()]);
+    $this->assertSame((string) Html::escape($author_name), (string) $output);
+    // Add comment field to user and term entities.
+    $this->addDefaultCommentField('user', 'user', 'comment', CommentItemInterface::OPEN, 'comment_user');
+    $this->addDefaultCommentField('taxonomy_term', 'tags', 'comment', CommentItemInterface::OPEN, 'comment_term');
+
+    // Create a user and a comment.
+    $user = User::create(['name' => 'alice']);
+    $user->activate();
+    $user->save();
+    $this->postComment($user, 'user body', 'user subject', TRUE);
+
+    // Create a term and a comment.
+    $term = Term::create([
+      'vid' => 'tags',
+      'name' => 'term',
+    ]);
+    $term->save();
+    $this->postComment($term, 'term body', 'term subject', TRUE);
+
+    // Load node, user and term again so comment_count gets computed.
+    $node = Node::load($node->id());
+    $user = User::load($user->id());
+    $term = Term::load($term->id());
+
+    // Generate comment tokens for node (it has 2 comments, both new),
+    // user and term.
+    $tests = [];
+    $tests['[entity:comment-count]'] = 2;
+    $tests['[entity:comment-count-new]'] = 2;
+    $tests['[node:comment-count]'] = 2;
+    $tests['[node:comment-count-new]'] = 2;
+    $tests['[user:comment-count]'] = 1;
+    $tests['[user:comment-count-new]'] = 1;
+    $tests['[term:comment-count]'] = 1;
+    $tests['[term:comment-count-new]'] = 1;
+
+    foreach ($tests as $input => $expected) {
+      $output = $token_service->replace($input, ['entity' => $node, 'node' => $node, 'user' => $user, 'term' => $term], ['langcode' => $language_interface->getId()]);
+      $this->assertSame((string) $expected, (string) $output, "Failed test case: {$input}");
+    }
+  }
+
+}

core/modules/comment/tests/src/Functional/CommentTranslationUITest.php

@@ -0,0 +1,242 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+use Drupal\comment\Plugin\Field\FieldType\CommentItemInterface;
+use Drupal\comment\Tests\CommentTestTrait;
+use Drupal\language\Entity\ConfigurableLanguage;
+use Drupal\Tests\content_translation\Functional\ContentTranslationUITestBase;
+
+/**
+ * Tests the Comment Translation UI.
+ *
+ * @group comment
+ */
+class CommentTranslationUITest extends ContentTranslationUITestBase {
+
+  use CommentTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * The subject of the test comment.
+   *
+   * @var string
+   */
+  protected $subject;
+
+  /**
+   * An administrative user with permission to administer comments.
+   *
+   * @var \Drupal\user\UserInterface
+   */
+  protected $adminUser;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultCacheContexts = [
+    'languages:language_interface',
+    'session',
+    'theme',
+    'timezone',
+    'url.query_args:_wrapper_format',
+    'url.query_args.pagers:0',
+    'url.site',
+    'user.permissions',
+    'user.roles',
+  ];
+
+  /**
+   * Modules to install.
+   *
+   * @var array
+   */
+  protected static $modules = [
+    'language',
+    'content_translation',
+    'node',
+    'comment',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    $this->entityTypeId = 'comment';
+    $this->bundle = 'comment_article';
+    $this->testLanguageSelector = FALSE;
+    $this->subject = $this->randomMachineName();
+    parent::setUp();
+    $this->doSetup();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setupBundle() {
+    parent::setupBundle();
+    $this->drupalCreateContentType(['type' => 'article', 'name' => 'article']);
+    // Add a comment field to the article content type.
+    $this->addDefaultCommentField('node', 'article', 'comment_article', CommentItemInterface::OPEN, 'comment_article');
+    // Create a page content type.
+    $this->drupalCreateContentType(['type' => 'page', 'name' => 'page']);
+    // Add a comment field to the page content type - this one won't be
+    // translatable.
+    $this->addDefaultCommentField('node', 'page', 'comment');
+    // Mark this bundle as translatable.
+    $this->container->get('content_translation.manager')->setEnabled('comment', 'comment_article', TRUE);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getTranslatorPermissions() {
+    return array_merge(parent::getTranslatorPermissions(), ['post comments', 'administer comments', 'access comments']);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function createEntity($values, $langcode, $comment_type = 'comment_article') {
+    if ($comment_type == 'comment_article') {
+      // This is the article node type, with the 'comment_article' field.
+      $node_type = 'article';
+      $field_name = 'comment_article';
+    }
+    else {
+      // This is the page node type with the non-translatable 'comment' field.
+      $node_type = 'page';
+      $field_name = 'comment';
+    }
+    $node = $this->drupalCreateNode([
+      'type' => $node_type,
+      $field_name => [
+        ['status' => CommentItemInterface::OPEN],
+      ],
+    ]);
+    $values['entity_id'] = $node->id();
+    $values['entity_type'] = 'node';
+    $values['field_name'] = $field_name;
+    $values['uid'] = $node->getOwnerId();
+    return parent::createEntity($values, $langcode, $comment_type);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getNewEntityValues($langcode) {
+    // Comment subject is not translatable hence we use a fixed value.
+    return [
+      'subject' => [['value' => $this->subject]],
+      'comment_body' => [['value' => $this->randomMachineName(16)]],
+    ] + parent::getNewEntityValues($langcode);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function doTestPublishedStatus() {
+    $entity_type_manager = \Drupal::entityTypeManager();
+    $storage = $entity_type_manager->getStorage($this->entityTypeId);
+
+    $storage->resetCache();
+    $entity = $storage->load($this->entityId);
+
+    // Unpublish translations.
+    foreach ($this->langcodes as $index => $langcode) {
+      if ($index > 0) {
+        $edit = ['status' => 0];
+        $url = $entity->toUrl('edit-form', ['language' => ConfigurableLanguage::load($langcode)]);
+        $this->drupalGet($url);
+        $this->submitForm($edit, $this->getFormSubmitAction($entity, $langcode));
+        $storage->resetCache();
+        $entity = $storage->load($this->entityId);
+        $this->assertFalse($this->manager->getTranslationMetadata($entity->getTranslation($langcode))->isPublished(), 'The translation has been correctly unpublished.');
+      }
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function doTestAuthoringInfo() {
+    $storage = $this->container->get('entity_type.manager')
+      ->getStorage($this->entityTypeId);
+    $storage->resetCache([$this->entityId]);
+    $entity = $storage->load($this->entityId);
+    $languages = $this->container->get('language_manager')->getLanguages();
+    $values = [];
+
+    // Post different authoring information for each translation.
+    foreach ($this->langcodes as $langcode) {
+      $url = $entity->toUrl('edit-form', ['language' => $languages[$langcode]]);
+      $user = $this->drupalCreateUser();
+      $values[$langcode] = [
+        'uid' => $user->id(),
+        'created' => \Drupal::time()->getRequestTime() - mt_rand(0, 1000),
+      ];
+      /** @var \Drupal\Core\Datetime\DateFormatterInterface $date_formatter */
+      $date_formatter = $this->container->get('date.formatter');
+      $edit = [
+        'uid' => $user->getAccountName() . ' (' . $user->id() . ')',
+        'date[date]' => $date_formatter->format($values[$langcode]['created'], 'custom', 'Y-m-d'),
+        'date[time]' => $date_formatter->format($values[$langcode]['created'], 'custom', 'H:i:s'),
+      ];
+      $this->drupalGet($url);
+      $this->submitForm($edit, $this->getFormSubmitAction($entity, $langcode));
+    }
+
+    $storage->resetCache([$this->entityId]);
+    $entity = $storage->load($this->entityId);
+    foreach ($this->langcodes as $langcode) {
+      $metadata = $this->manager->getTranslationMetadata($entity->getTranslation($langcode));
+      $this->assertEquals($values[$langcode]['uid'], $metadata->getAuthor()->id(), 'Translation author correctly stored.');
+      $this->assertEquals($values[$langcode]['created'], $metadata->getCreatedTime(), 'Translation date correctly stored.');
+    }
+  }
+
+  /**
+   * Tests translate link on comment content admin page.
+   */
+  public function testTranslateLinkCommentAdminPage(): void {
+    $this->adminUser = $this->drupalCreateUser(array_merge(parent::getTranslatorPermissions(), ['access administration pages', 'administer comments', 'skip comment approval']));
+    $this->drupalLogin($this->adminUser);
+
+    $cid_translatable = $this->createEntity([], $this->langcodes[0]);
+    $cid_untranslatable = $this->createEntity([], $this->langcodes[0], 'comment');
+
+    // Verify translation links.
+    $this->drupalGet('admin/content/comment');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->linkByHrefExists('comment/' . $cid_translatable . '/translations');
+    $this->assertSession()->linkByHrefNotExists('comment/' . $cid_untranslatable . '/translations');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function doTestTranslationEdit() {
+    $storage = $this->container->get('entity_type.manager')
+      ->getStorage($this->entityTypeId);
+    $storage->resetCache([$this->entityId]);
+    $entity = $storage->load($this->entityId);
+    $languages = $this->container->get('language_manager')->getLanguages();
+
+    foreach ($this->langcodes as $langcode) {
+      // We only want to test the title for non-english translations.
+      if ($langcode != 'en') {
+        $options = ['language' => $languages[$langcode]];
+        $url = $entity->toUrl('edit-form', $options);
+        $this->drupalGet($url);
+        $this->assertSession()->pageTextContains("Edit {$this->entityTypeId} {$entity->getTranslation($langcode)->label()} [{$languages[$langcode]->getName()} translation]");
+      }
+    }
+  }
+
+}

core/modules/comment/tests/src/Functional/CommentTypeTest.php

@@ -0,0 +1,214 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+use Drupal\Core\Url;
+use Drupal\comment\Entity\Comment;
+use Drupal\comment\Entity\CommentType;
+use Drupal\comment\Plugin\Field\FieldType\CommentItemInterface;
+use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\field\Entity\FieldConfig;
+use Drupal\node\Entity\Node;
+
+/**
+ * Ensures that comment type functions work correctly.
+ *
+ * @group comment
+ */
+class CommentTypeTest extends CommentTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Admin user.
+   *
+   * @var \Drupal\Core\Session\AccountInterface
+   */
+  protected $adminUser;
+
+  /**
+   * Permissions to grant admin user.
+   *
+   * @var array
+   */
+  protected $permissions = [
+    'administer comments',
+    'administer comment fields',
+    'administer comment types',
+  ];
+
+  /**
+   * Sets the test up.
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->drupalPlaceBlock('page_title_block');
+    $this->drupalPlaceBlock('system_breadcrumb_block');
+
+    $this->adminUser = $this->drupalCreateUser($this->permissions);
+  }
+
+  /**
+   * Tests creating a comment type programmatically and via a form.
+   */
+  public function testCommentTypeCreation(): void {
+    // Create a comment type programmatically.
+    $type = $this->createCommentType('other');
+
+    $comment_type = CommentType::load('other');
+    $this->assertInstanceOf(CommentType::class, $comment_type);
+
+    // Log in a test user.
+    $this->drupalLogin($this->adminUser);
+
+    // Ensure that the new comment type admin page can be accessed.
+    $this->drupalGet('admin/structure/comment/manage/' . $type->id());
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->elementTextEquals('css', 'h1', "Edit {$comment_type->label()} comment type");
+
+    // Create a comment type via the user interface.
+    $edit = [
+      'id' => 'foo',
+      'label' => 'title for foo',
+      'description' => '',
+    ];
+    $this->drupalGet('admin/structure/comment/types/add');
+
+    // Ensure that target entity type is a required field.
+    $this->submitForm($edit, 'Save and manage fields');
+    $this->assertSession()->pageTextContains('Target entity type field is required.');
+
+    // Ensure that comment type is saved when target entity type is provided.
+    $edit['target_entity_type_id'] = 'node';
+    $this->submitForm($edit, 'Save and manage fields');
+    $this->assertSession()->pageTextContains('Comment type title for foo has been added.');
+
+    // Asserts that form submit redirects to the expected manage fields page.
+    $this->assertSession()->addressEquals('admin/structure/comment/manage/' . $edit['id'] . '/fields');
+
+    // Asserts that the comment type is visible in breadcrumb.
+    $this->assertTrue($this->assertSession()->elementExists('css', 'nav[role="navigation"]')->hasLink('title for foo'));
+
+    $comment_type = CommentType::load('foo');
+    $this->assertInstanceOf(CommentType::class, $comment_type);
+
+    // Check that the comment type was created in site default language.
+    $default_langcode = \Drupal::languageManager()->getDefaultLanguage()->getId();
+    $this->assertEquals($default_langcode, $comment_type->language()->getId());
+
+    // Edit the comment-type and ensure that we cannot change the entity-type.
+    $this->drupalGet('admin/structure/comment/manage/foo');
+    $this->assertSession()->fieldNotExists('target_entity_type_id');
+    $this->assertSession()->pageTextContains('Target entity type');
+    // Save the form and ensure the entity-type value is preserved even though
+    // the field isn't present.
+    $this->submitForm([], 'Save');
+    \Drupal::entityTypeManager()->getStorage('comment_type')->resetCache(['foo']);
+    $comment_type = CommentType::load('foo');
+    $this->assertEquals('node', $comment_type->getTargetEntityTypeId());
+
+    // Ensure that target type is displayed in the comment type list.
+    $this->drupalGet('admin/structure/comment');
+    $this->assertSession()->elementExists('xpath', '//td[text() = "Content"]');
+  }
+
+  /**
+   * Tests editing a comment type using the UI.
+   */
+  public function testCommentTypeEditing(): void {
+    $this->drupalLogin($this->adminUser);
+
+    $field = FieldConfig::loadByName('comment', 'comment', 'comment_body');
+    $this->assertEquals('Comment', $field->getLabel(), 'Comment body field was found.');
+
+    // Change the comment type name.
+    $this->drupalGet('admin/structure/comment');
+    $edit = [
+      'label' => 'Bar',
+    ];
+    $this->drupalGet('admin/structure/comment/manage/comment');
+    $this->submitForm($edit, 'Save');
+
+    $this->drupalGet('admin/structure/comment');
+    $this->assertSession()->pageTextContains('Bar');
+    $this->clickLink('Manage fields');
+    // Verify that the original machine name was used in the URL.
+    $this->assertSession()->addressEquals(Url::fromRoute('entity.comment.field_ui_fields', ['comment_type' => 'comment']));
+    $this->assertCount(1, $this->cssSelect('tr#comment-body'), 'Body field exists.');
+
+    // Remove the body field.
+    $this->drupalGet('admin/structure/comment/manage/comment/fields/comment.comment.comment_body/delete');
+    $this->submitForm([], 'Delete');
+    // Resave the settings for this type.
+    $this->drupalGet('admin/structure/comment/manage/comment');
+    $this->submitForm([], 'Save');
+    // Check that the body field doesn't exist.
+    $this->drupalGet('admin/structure/comment/manage/comment/fields');
+    $this->assertCount(0, $this->cssSelect('tr#comment-body'), 'Body field does not exist.');
+  }
+
+  /**
+   * Tests deleting a comment type that still has content.
+   */
+  public function testCommentTypeDeletion(): void {
+    // Create a comment type programmatically.
+    $type = $this->createCommentType('foo');
+    $this->drupalCreateContentType(['type' => 'page']);
+    $this->addDefaultCommentField('node', 'page', 'foo', CommentItemInterface::OPEN, 'foo');
+    $field_storage = FieldStorageConfig::loadByName('node', 'foo');
+
+    $this->drupalLogin($this->adminUser);
+
+    // Create a node.
+    $node = Node::create([
+      'type' => 'page',
+      'title' => 'foo',
+    ]);
+    $node->save();
+
+    // Add a new comment of this type.
+    $comment = Comment::create([
+      'comment_type' => 'foo',
+      'entity_type' => 'node',
+      'field_name' => 'foo',
+      'entity_id' => $node->id(),
+    ]);
+    $comment->save();
+
+    // Attempt to delete the comment type, which should not be allowed.
+    $this->drupalGet('admin/structure/comment/manage/' . $type->id() . '/delete');
+    $this->assertSession()->pageTextContains($type->label() . ' is used by 1 comment on your site. You can not remove this comment type until you have removed all of the ' . $type->label() . ' comments.');
+    $this->assertSession()->pageTextContains('foo is used by the node.foo field on your site. You can not remove this comment type until you have removed the field.');
+    $this->assertSession()->pageTextNotContains('This action cannot be undone.');
+
+    // Delete the comment and the field.
+    $comment->delete();
+    $field_storage->delete();
+    // Attempt to delete the comment type, which should now be allowed.
+    $this->drupalGet('admin/structure/comment/manage/' . $type->id() . '/delete');
+    $this->assertSession()->pageTextContains('Are you sure you want to delete the comment type ' . $type->id() . '?');
+    $this->assertSession()->pageTextContains('This action cannot be undone.');
+
+    // Test exception thrown when re-using an existing comment type.
+    try {
+      $this->addDefaultCommentField('comment', 'comment', 'bar');
+      $this->fail('Exception not thrown.');
+    }
+    catch (\InvalidArgumentException $e) {
+      // Expected exception; just continue testing.
+    }
+
+    // Delete the comment type.
+    $this->drupalGet('admin/structure/comment/manage/' . $type->id() . '/delete');
+    $this->submitForm([], 'Delete');
+    $this->assertNull(CommentType::load($type->id()), 'Comment type deleted.');
+    $this->assertSession()->pageTextContains('The comment type ' . $type->label() . ' has been deleted.');
+  }
+
+}

core/modules/comment/tests/src/Functional/GenericTest.php

@@ -0,0 +1,14 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional;
+
+use Drupal\Tests\system\Functional\Module\GenericModuleTestBase;
+
+/**
+ * Generic module test for comment.
+ *
+ * @group comment
+ */
+class GenericTest extends GenericModuleTestBase {}

core/modules/comment/tests/src/Functional/Rest/CommentJsonAnonTest.php

@@ -0,0 +1,53 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional\Rest;
+
+use Drupal\Tests\rest\Functional\AnonResourceTestTrait;
+
+/**
+ * @group rest
+ * @group #slow
+ */
+class CommentJsonAnonTest extends CommentResourceTestBase {
+
+  use AnonResourceTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $format = 'json';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $mimeType = 'application/json';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   *
+   * Anonymous users cannot edit their own comments.
+   *
+   * @see \Drupal\comment\CommentAccessControlHandler::checkAccess
+   *
+   * Therefore we grant them the 'administer comments' permission for the
+   * purpose of this test.
+   *
+   * @see ::setUpAuthorization
+   */
+  protected static $patchProtectedFieldNames = [
+    'pid' => NULL,
+    'entity_id' => NULL,
+    'changed' => NULL,
+    'thread' => NULL,
+    'entity_type' => NULL,
+    'field_name' => NULL,
+  ];
+
+}

core/modules/comment/tests/src/Functional/Rest/CommentJsonBasicAuthTest.php

@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional\Rest;
+
+use Drupal\Tests\rest\Functional\BasicAuthResourceTestTrait;
+
+/**
+ * @group rest
+ * @group #slow
+ */
+class CommentJsonBasicAuthTest extends CommentResourceTestBase {
+
+  use BasicAuthResourceTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['basic_auth'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $format = 'json';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $mimeType = 'application/json';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $auth = 'basic_auth';
+
+}

core/modules/comment/tests/src/Functional/Rest/CommentJsonCookieTest.php

@@ -0,0 +1,37 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional\Rest;
+
+use Drupal\Tests\rest\Functional\CookieResourceTestTrait;
+
+/**
+ * @group rest
+ * @group #slow
+ */
+class CommentJsonCookieTest extends CommentResourceTestBase {
+
+  use CookieResourceTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $format = 'json';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $mimeType = 'application/json';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $auth = 'cookie';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+}

core/modules/comment/tests/src/Functional/Rest/CommentResourceTestBase.php

@@ -0,0 +1,386 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional\Rest;
+
+use Drupal\comment\Entity\Comment;
+use Drupal\comment\Entity\CommentType;
+use Drupal\comment\Plugin\Field\FieldType\CommentItemInterface;
+use Drupal\comment\Tests\CommentTestTrait;
+use Drupal\Core\Cache\Cache;
+use Drupal\entity_test\Entity\EntityTest;
+use Drupal\Tests\rest\Functional\EntityResource\EntityResourceTestBase;
+use Drupal\user\Entity\User;
+use GuzzleHttp\RequestOptions;
+
+abstract class CommentResourceTestBase extends EntityResourceTestBase {
+
+  use CommentTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['comment', 'entity_test'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $entityTypeId = 'comment';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $patchProtectedFieldNames = [
+    'status' => "The 'administer comments' permission is required.",
+    'uid' => "The 'administer comments' permission is required.",
+    'pid' => NULL,
+    'entity_id' => NULL,
+    'name' => "The 'administer comments' permission is required.",
+    'homepage' => "The 'administer comments' permission is required.",
+    'created' => "The 'administer comments' permission is required.",
+    'changed' => NULL,
+    'thread' => NULL,
+    'entity_type' => NULL,
+    'field_name' => NULL,
+  ];
+
+  /**
+   * @var \Drupal\comment\CommentInterface
+   */
+  protected $entity;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUpAuthorization($method) {
+    switch ($method) {
+      case 'GET':
+        $this->grantPermissionsToTestedRole(['access comments', 'view test entity']);
+        break;
+
+      case 'POST':
+        $this->grantPermissionsToTestedRole(['post comments']);
+        break;
+
+      case 'PATCH':
+        // Anonymous users are not ever allowed to edit their own comments. To
+        // be able to test PATCHing comments as the anonymous user, the more
+        // permissive 'administer comments' permission must be granted.
+        // @see \Drupal\comment\CommentAccessControlHandler::checkAccess
+        if (static::$auth) {
+          $this->grantPermissionsToTestedRole(['edit own comments']);
+        }
+        else {
+          $this->grantPermissionsToTestedRole(['administer comments']);
+        }
+        break;
+
+      case 'DELETE':
+        $this->grantPermissionsToTestedRole(['administer comments']);
+        break;
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function createEntity() {
+    // Create a "bar" bundle for the "entity_test" entity type and create.
+    $bundle = 'bar';
+    entity_test_create_bundle($bundle, NULL, 'entity_test');
+
+    // Create a comment field on this bundle.
+    $this->addDefaultCommentField('entity_test', 'bar', 'comment');
+
+    // Create a "Camelids" test entity that the comment will be assigned to.
+    $commented_entity = EntityTest::create([
+      'name' => 'Camelids',
+      'type' => 'bar',
+      'comment' => CommentItemInterface::OPEN,
+    ]);
+    $commented_entity->save();
+
+    // Create a "Llama" comment.
+    $comment = Comment::create([
+      'comment_body' => [
+        'value' => 'The name "llama" was adopted by European settlers from native Peruvians.',
+        'format' => 'plain_text',
+      ],
+      'entity_id' => $commented_entity->id(),
+      'entity_type' => 'entity_test',
+      'field_name' => 'comment',
+    ]);
+    $comment->setSubject('Llama')
+      ->setOwnerId(static::$auth ? $this->account->id() : 0)
+      ->setPublished()
+      ->setCreatedTime(123456789)
+      ->setChangedTime(123456789);
+    $comment->save();
+
+    return $comment;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getExpectedNormalizedEntity() {
+    $author = User::load($this->entity->getOwnerId());
+    return [
+      'cid' => [
+        ['value' => 1],
+      ],
+      'uuid' => [
+        ['value' => $this->entity->uuid()],
+      ],
+      'langcode' => [
+        [
+          'value' => 'en',
+        ],
+      ],
+      'comment_type' => [
+        [
+          'target_id' => 'comment',
+          'target_type' => 'comment_type',
+          'target_uuid' => CommentType::load('comment')->uuid(),
+        ],
+      ],
+      'subject' => [
+        [
+          'value' => 'Llama',
+        ],
+      ],
+      'status' => [
+        [
+          'value' => TRUE,
+        ],
+      ],
+      'created' => [
+        [
+          'value' => (new \DateTime())->setTimestamp(123456789)->setTimezone(new \DateTimeZone('UTC'))->format(\DateTime::RFC3339),
+          'format' => \DateTime::RFC3339,
+        ],
+      ],
+      'changed' => [
+        [
+          'value' => (new \DateTime())->setTimestamp((int) $this->entity->getChangedTime())->setTimezone(new \DateTimeZone('UTC'))->format(\DateTime::RFC3339),
+          'format' => \DateTime::RFC3339,
+        ],
+      ],
+      'default_langcode' => [
+        [
+          'value' => TRUE,
+        ],
+      ],
+      'uid' => [
+        [
+          'target_id' => (int) $author->id(),
+          'target_type' => 'user',
+          'target_uuid' => $author->uuid(),
+          'url' => base_path() . 'user/' . $author->id(),
+        ],
+      ],
+      'pid' => [],
+      'entity_type' => [
+        [
+          'value' => 'entity_test',
+        ],
+      ],
+      'entity_id' => [
+        [
+          'target_id' => 1,
+          'target_type' => 'entity_test',
+          'target_uuid' => EntityTest::load(1)->uuid(),
+          'url' => base_path() . 'entity_test/1',
+        ],
+      ],
+      'field_name' => [
+        [
+          'value' => 'comment',
+        ],
+      ],
+      'name' => [],
+      'homepage' => [],
+      'thread' => [
+        [
+          'value' => '01/',
+        ],
+      ],
+      'comment_body' => [
+        [
+          'value' => 'The name "llama" was adopted by European settlers from native Peruvians.',
+          'format' => 'plain_text',
+          'processed' => '<p>The name &quot;llama&quot; was adopted by European settlers from native Peruvians.</p>' . "\n",
+        ],
+      ],
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getNormalizedPostEntity() {
+    return [
+      'comment_type' => [
+        [
+          'target_id' => 'comment',
+        ],
+      ],
+      'entity_type' => [
+        [
+          'value' => 'entity_test',
+        ],
+      ],
+      'entity_id' => [
+        [
+          'target_id' => (int) EntityTest::load(1)->id(),
+        ],
+      ],
+      'field_name' => [
+        [
+          'value' => 'comment',
+        ],
+      ],
+      'subject' => [
+        [
+          'value' => 'Drama llama',
+        ],
+      ],
+      'comment_body' => [
+        [
+          'value' => 'Llamas are awesome.',
+          'format' => 'plain_text',
+        ],
+      ],
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getNormalizedPatchEntity() {
+    return array_diff_key($this->getNormalizedPostEntity(), ['entity_type' => TRUE, 'entity_id' => TRUE, 'field_name' => TRUE]);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getExpectedCacheTags() {
+    return Cache::mergeTags(parent::getExpectedCacheTags(), ['config:filter.format.plain_text']);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getExpectedCacheContexts() {
+    return Cache::mergeContexts(['languages:language_interface', 'theme'], parent::getExpectedCacheContexts());
+  }
+
+  /**
+   * Tests POSTing a comment without critical base fields.
+   *
+   * Tests with the most minimal normalization possible: the one returned by
+   * ::getNormalizedPostEntity().
+   *
+   * But Comment entities have some very special edge cases:
+   * - base fields that are not marked as required in
+   *   \Drupal\comment\Entity\Comment::baseFieldDefinitions() yet in fact are
+   *   required.
+   * - base fields that are marked as required, but yet can still result in
+   *   validation errors other than "missing required field".
+   */
+  public function testPostDxWithoutCriticalBaseFields(): void {
+    $this->initAuthentication();
+    $this->provisionEntityResource();
+    $this->setUpAuthorization('POST');
+
+    $url = $this->getEntityResourcePostUrl()->setOption('query', ['_format' => static::$format]);
+    $request_options = [];
+    $request_options[RequestOptions::HEADERS]['Accept'] = static::$mimeType;
+    $request_options[RequestOptions::HEADERS]['Content-Type'] = static::$mimeType;
+    $request_options = array_merge_recursive($request_options, $this->getAuthenticationRequestOptions('POST'));
+
+    // DX: 422 when missing 'entity_type' field.
+    $request_options[RequestOptions::BODY] = $this->serializer->encode(array_diff_key($this->getNormalizedPostEntity(), ['entity_type' => TRUE]), static::$format);
+    $response = $this->request('POST', $url, $request_options);
+    $this->assertResourceErrorResponse(422, "Unprocessable Entity: validation failed.\nentity_type: This value should not be null.\n", $response);
+
+    // DX: 422 when missing 'entity_id' field.
+    $request_options[RequestOptions::BODY] = $this->serializer->encode(array_diff_key($this->getNormalizedPostEntity(), ['entity_id' => TRUE]), static::$format);
+    $response = $this->request('POST', $url, $request_options);
+    $this->assertResourceErrorResponse(422, "Unprocessable Entity: validation failed.\nentity_id: This value should not be null.\n", $response);
+
+    // DX: 422 when missing 'field_name' field.
+    $request_options[RequestOptions::BODY] = $this->serializer->encode(array_diff_key($this->getNormalizedPostEntity(), ['field_name' => TRUE]), static::$format);
+    $response = $this->request('POST', $url, $request_options);
+    $this->assertResourceErrorResponse(422, "Unprocessable Entity: validation failed.\nfield_name: This value should not be null.\n", $response);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getExpectedUnauthorizedAccessMessage($method) {
+    switch ($method) {
+      case 'GET':
+        return "The 'access comments' permission is required and the comment must be published.";
+
+      case 'POST':
+        return "The 'post comments' permission is required.";
+
+      case 'PATCH':
+        return "The 'edit own comments' permission is required, the user must be the comment author, and the comment must be published.";
+
+      case 'DELETE':
+      default:
+        // \Drupal\comment\CommentAccessControlHandler::checkAccess() does not
+        // specify a reason for not allowing a comment to be deleted.
+        return '';
+    }
+  }
+
+  /**
+   * Tests POSTing a comment with and without 'skip comment approval'.
+   */
+  public function testPostSkipCommentApproval(): void {
+    $this->initAuthentication();
+    $this->provisionEntityResource();
+    $this->setUpAuthorization('POST');
+
+    // Create request.
+    $request_options = [];
+    $request_options[RequestOptions::HEADERS]['Accept'] = static::$mimeType;
+    $request_options[RequestOptions::HEADERS]['Content-Type'] = static::$mimeType;
+    $request_options = array_merge_recursive($request_options, $this->getAuthenticationRequestOptions('POST'));
+    $request_options[RequestOptions::BODY] = $this->serializer->encode($this->getNormalizedPostEntity(), static::$format);
+
+    $url = $this->getEntityResourcePostUrl()->setOption('query', ['_format' => static::$format]);
+
+    // Status should be FALSE when posting as anonymous.
+    $response = $this->request('POST', $url, $request_options);
+    $unserialized = $this->serializer->deserialize((string) $response->getBody(), get_class($this->entity), static::$format);
+    $this->assertResourceResponse(201, FALSE, $response);
+    $this->assertFalse($unserialized->isPublished());
+
+    // Make sure the role save below properly invalidates cache tags.
+    $this->refreshVariables();
+
+    // Grant anonymous permission to skip comment approval.
+    $this->grantPermissionsToTestedRole(['skip comment approval']);
+
+    // Status should be TRUE when posting as anonymous and skip comment approval.
+    $response = $this->request('POST', $url, $request_options);
+    $unserialized = $this->serializer->deserialize((string) $response->getBody(), get_class($this->entity), static::$format);
+    $this->assertResourceResponse(201, FALSE, $response);
+    $this->assertTrue($unserialized->isPublished());
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getExpectedUnauthorizedEntityAccessCacheability($is_authenticated) {
+    // @see \Drupal\comment\CommentAccessControlHandler::checkAccess()
+    return parent::getExpectedUnauthorizedEntityAccessCacheability($is_authenticated)
+      ->addCacheTags(['comment:1']);
+  }
+
+}

core/modules/comment/tests/src/Functional/Rest/CommentTypeJsonAnonTest.php

@@ -0,0 +1,31 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional\Rest;
+
+use Drupal\Tests\rest\Functional\AnonResourceTestTrait;
+
+/**
+ * @group rest
+ */
+class CommentTypeJsonAnonTest extends CommentTypeResourceTestBase {
+
+  use AnonResourceTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $format = 'json';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $mimeType = 'application/json';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+}

core/modules/comment/tests/src/Functional/Rest/CommentTypeJsonBasicAuthTest.php

@@ -0,0 +1,41 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional\Rest;
+
+use Drupal\Tests\rest\Functional\BasicAuthResourceTestTrait;
+
+/**
+ * @group rest
+ */
+class CommentTypeJsonBasicAuthTest extends CommentTypeResourceTestBase {
+
+  use BasicAuthResourceTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['basic_auth'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $format = 'json';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $mimeType = 'application/json';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $auth = 'basic_auth';
+
+}

core/modules/comment/tests/src/Functional/Rest/CommentTypeJsonCookieTest.php

@@ -0,0 +1,36 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional\Rest;
+
+use Drupal\Tests\rest\Functional\CookieResourceTestTrait;
+
+/**
+ * @group rest
+ */
+class CommentTypeJsonCookieTest extends CommentTypeResourceTestBase {
+
+  use CookieResourceTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $format = 'json';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $mimeType = 'application/json';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $auth = 'cookie';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+}

core/modules/comment/tests/src/Functional/Rest/CommentTypeResourceTestBase.php

@@ -0,0 +1,80 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional\Rest;
+
+use Drupal\comment\Entity\CommentType;
+use Drupal\Tests\rest\Functional\EntityResource\ConfigEntityResourceTestBase;
+
+/**
+ * ResourceTestBase for CommentType entity.
+ */
+abstract class CommentTypeResourceTestBase extends ConfigEntityResourceTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['node', 'comment'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $entityTypeId = 'comment_type';
+
+  /**
+   * The CommentType entity.
+   *
+   * @var \Drupal\comment\CommentTypeInterface
+   */
+  protected $entity;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUpAuthorization($method) {
+    $this->grantPermissionsToTestedRole(['administer comment types']);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function createEntity() {
+    // Create a "Camelids" comment type.
+    $camelids = CommentType::create([
+      'id' => 'camelids',
+      'label' => 'Camelids',
+      'description' => 'Camelids are large, strictly herbivorous animals with slender necks and long legs.',
+      'target_entity_type_id' => 'node',
+    ]);
+
+    $camelids->save();
+
+    return $camelids;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getExpectedNormalizedEntity() {
+    return [
+      'dependencies' => [],
+      'description' => 'Camelids are large, strictly herbivorous animals with slender necks and long legs.',
+      'id' => 'camelids',
+      'label' => 'Camelids',
+      'langcode' => 'en',
+      'status' => TRUE,
+      'target_entity_type_id' => 'node',
+      'uuid' => $this->entity->uuid(),
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getNormalizedPostEntity() {
+    // @todo Update in https://www.drupal.org/node/2300677.
+    return [];
+  }
+
+}

core/modules/comment/tests/src/Functional/Rest/CommentTypeXmlAnonTest.php

@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional\Rest;
+
+use Drupal\Tests\rest\Functional\AnonResourceTestTrait;
+use Drupal\Tests\rest\Functional\EntityResource\XmlEntityNormalizationQuirksTrait;
+
+/**
+ * @group rest
+ */
+class CommentTypeXmlAnonTest extends CommentTypeResourceTestBase {
+
+  use AnonResourceTestTrait;
+  use XmlEntityNormalizationQuirksTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $format = 'xml';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $mimeType = 'text/xml; charset=UTF-8';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+}

core/modules/comment/tests/src/Functional/Rest/CommentTypeXmlBasicAuthTest.php

@@ -0,0 +1,43 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional\Rest;
+
+use Drupal\Tests\rest\Functional\BasicAuthResourceTestTrait;
+use Drupal\Tests\rest\Functional\EntityResource\XmlEntityNormalizationQuirksTrait;
+
+/**
+ * @group rest
+ */
+class CommentTypeXmlBasicAuthTest extends CommentTypeResourceTestBase {
+
+  use BasicAuthResourceTestTrait;
+  use XmlEntityNormalizationQuirksTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['basic_auth'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $format = 'xml';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $mimeType = 'text/xml; charset=UTF-8';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $auth = 'basic_auth';
+
+}

core/modules/comment/tests/src/Functional/Rest/CommentTypeXmlCookieTest.php

@@ -0,0 +1,38 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional\Rest;
+
+use Drupal\Tests\rest\Functional\CookieResourceTestTrait;
+use Drupal\Tests\rest\Functional\EntityResource\XmlEntityNormalizationQuirksTrait;
+
+/**
+ * @group rest
+ */
+class CommentTypeXmlCookieTest extends CommentTypeResourceTestBase {
+
+  use CookieResourceTestTrait;
+  use XmlEntityNormalizationQuirksTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $format = 'xml';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $mimeType = 'text/xml; charset=UTF-8';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $auth = 'cookie';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+}

core/modules/comment/tests/src/Functional/Rest/CommentXmlAnonTest.php

@@ -0,0 +1,71 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional\Rest;
+
+use Drupal\Tests\rest\Functional\AnonResourceTestTrait;
+use Drupal\Tests\rest\Functional\EntityResource\XmlEntityNormalizationQuirksTrait;
+
+/**
+ * @group rest
+ * @group #slow
+ */
+class CommentXmlAnonTest extends CommentResourceTestBase {
+
+  use AnonResourceTestTrait;
+  use XmlEntityNormalizationQuirksTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $format = 'xml';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $mimeType = 'text/xml; charset=UTF-8';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   *
+   * Anonymous users cannot edit their own comments.
+   *
+   * @see \Drupal\comment\CommentAccessControlHandler::checkAccess
+   *
+   * Therefore we grant them the 'administer comments' permission for the
+   * purpose of this test.
+   *
+   * @see ::setUpAuthorization
+   */
+  protected static $patchProtectedFieldNames = [
+    'pid',
+    'entity_id',
+    'changed',
+    'thread',
+    'entity_type',
+    'field_name',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  public function testPostDxWithoutCriticalBaseFields(): void {
+    // Deserialization of the XML format is not supported.
+    $this->markTestSkipped();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function testPostSkipCommentApproval(): void {
+    // Deserialization of the XML format is not supported.
+    $this->markTestSkipped();
+  }
+
+}

core/modules/comment/tests/src/Functional/Rest/CommentXmlBasicAuthTest.php

@@ -0,0 +1,60 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional\Rest;
+
+use Drupal\Tests\rest\Functional\BasicAuthResourceTestTrait;
+use Drupal\Tests\rest\Functional\EntityResource\XmlEntityNormalizationQuirksTrait;
+
+/**
+ * @group rest
+ * @group #slow
+ */
+class CommentXmlBasicAuthTest extends CommentResourceTestBase {
+
+  use BasicAuthResourceTestTrait;
+  use XmlEntityNormalizationQuirksTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['basic_auth'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $format = 'xml';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $mimeType = 'text/xml; charset=UTF-8';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $auth = 'basic_auth';
+
+  /**
+   * {@inheritdoc}
+   */
+  public function testPostDxWithoutCriticalBaseFields(): void {
+    // Deserialization of the XML format is not supported.
+    $this->markTestSkipped();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function testPostSkipCommentApproval(): void {
+    // Deserialization of the XML format is not supported.
+    $this->markTestSkipped();
+  }
+
+}

core/modules/comment/tests/src/Functional/Rest/CommentXmlCookieTest.php

@@ -0,0 +1,55 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional\Rest;
+
+use Drupal\Tests\rest\Functional\CookieResourceTestTrait;
+use Drupal\Tests\rest\Functional\EntityResource\XmlEntityNormalizationQuirksTrait;
+
+/**
+ * @group rest
+ * @group #slow
+ */
+class CommentXmlCookieTest extends CommentResourceTestBase {
+
+  use CookieResourceTestTrait;
+  use XmlEntityNormalizationQuirksTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $format = 'xml';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $mimeType = 'text/xml; charset=UTF-8';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $auth = 'cookie';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  public function testPostDxWithoutCriticalBaseFields(): void {
+    // Deserialization of the XML format is not supported.
+    $this->markTestSkipped();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function testPostSkipCommentApproval(): void {
+    // Deserialization of the XML format is not supported.
+    $this->markTestSkipped();
+  }
+
+}

core/modules/comment/tests/src/Functional/Views/CommentAdminTest.php

@@ -0,0 +1,254 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional\Views;
+
+use Drupal\block_content\Entity\BlockContent;
+use Drupal\block_content\Entity\BlockContentType;
+use Drupal\comment\CommentInterface;
+use Drupal\comment\Entity\Comment;
+use Drupal\comment\Plugin\Field\FieldType\CommentItemInterface;
+use Drupal\language\Entity\ConfigurableLanguage;
+use Drupal\Tests\comment\Functional\CommentTestBase as CommentBrowserTestBase;
+use Drupal\Component\Utility\Html;
+use Drupal\Component\Utility\Unicode;
+use Drupal\user\RoleInterface;
+use Drupal\views\Views;
+
+/**
+ * Tests comment approval functionality.
+ *
+ * @group comment
+ */
+class CommentAdminTest extends CommentBrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'language',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    // Make the site multilingual to have a working language field handler.
+    ConfigurableLanguage::create([
+      'id' => 'es',
+      'title' => 'Spanish title',
+      'label' => 'Spanish label',
+    ])->save();
+    \Drupal::service('module_installer')->install(['views']);
+    $view = Views::getView('comment');
+    $view->storage->enable()->save();
+    \Drupal::service('router.builder')->rebuildIfNeeded();
+  }
+
+  /**
+   * Tests comment approval functionality through admin/content/comment.
+   */
+  public function testApprovalAdminInterface(): void {
+    // Set anonymous comments to require approval.
+    user_role_change_permissions(RoleInterface::ANONYMOUS_ID, [
+      'access comments' => TRUE,
+      'post comments' => TRUE,
+      'skip comment approval' => FALSE,
+    ]);
+    $this->drupalPlaceBlock('page_title_block');
+    $this->drupalLogin($this->adminUser);
+    // Ensure that doesn't require contact info.
+    $this->setCommentAnonymous(CommentInterface::ANONYMOUS_MAYNOT_CONTACT);
+
+    // Test that the comments page loads correctly when there are no comments.
+    $this->drupalGet('admin/content/comment');
+    $this->assertSession()->pageTextContains('No comments available.');
+
+    // Assert the expose filters on the admin page.
+    $this->assertSession()->fieldExists('subject');
+    $this->assertSession()->fieldExists('author_name');
+    $this->assertSession()->fieldExists('langcode');
+
+    $this->drupalLogout();
+
+    // Post anonymous comment without contact info.
+    $body = $this->getRandomGenerator()->sentences(4);
+    $subject = Unicode::truncate(trim(Html::decodeEntities(strip_tags($body))), 29, TRUE, TRUE);
+    $author_name = $this->randomMachineName();
+    $this->drupalGet('comment/reply/node/' . $this->node->id() . '/comment');
+    $this->submitForm([
+      'name' => $author_name,
+      'comment_body[0][value]' => $body,
+    ], 'Save');
+    $this->assertSession()->pageTextContains('Your comment has been queued for review by site administrators and will be published after approval.');
+
+    // Get unapproved comment id.
+    $this->drupalLogin($this->adminUser);
+    $anonymous_comment4 = $this->getUnapprovedComment($subject);
+    $anonymous_comment4 = Comment::create([
+      'cid' => $anonymous_comment4,
+      'subject' => $subject,
+      'comment_body' => $body,
+      'entity_id' => $this->node->id(),
+      'entity_type' => 'node',
+      'field_name' => 'comment',
+    ]);
+    $this->drupalLogout();
+
+    $this->assertFalse($this->commentExists($anonymous_comment4), 'Anonymous comment was not published.');
+
+    // Approve comment.
+    $this->drupalLogin($this->adminUser);
+    $edit = [];
+    $edit['action'] = 'comment_publish_action';
+    $edit['comment_bulk_form[0]'] = $anonymous_comment4->id();
+    $this->drupalGet('admin/content/comment/approval');
+    $this->submitForm($edit, 'Apply to selected items');
+
+    $this->assertSession()->pageTextContains('Publish comment was applied to 1 item.');
+    $this->drupalLogout();
+
+    $this->drupalGet('node/' . $this->node->id());
+    $this->assertTrue($this->commentExists($anonymous_comment4), 'Anonymous comment visible.');
+
+    // Post 2 anonymous comments without contact info.
+    $comments[] = $this->postComment($this->node, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+    $comments[] = $this->postComment($this->node, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+
+    // Publish multiple comments in one operation.
+    $this->drupalLogin($this->adminUser);
+    $this->drupalGet('admin/content/comment/approval');
+    $this->assertSession()->pageTextContains('Unapproved comments (2)');
+
+    // Assert the expose filters on the admin page.
+    $this->assertSession()->fieldExists('subject');
+    $this->assertSession()->fieldExists('author_name');
+    $this->assertSession()->fieldExists('langcode');
+
+    $edit = [
+      "action" => 'comment_publish_action',
+      "comment_bulk_form[1]" => $comments[0]->id(),
+      "comment_bulk_form[0]" => $comments[1]->id(),
+    ];
+    $this->submitForm($edit, 'Apply to selected items');
+    $this->assertSession()->pageTextContains('Unapproved comments (0)');
+
+    // Test message when no comments selected.
+    $this->drupalGet('admin/content/comment');
+    $this->submitForm([], 'Apply to selected items');
+    $this->assertSession()->pageTextContains('Select one or more comments to perform the update on.');
+
+    // Test that comment listing shows the correct subject link.
+    $this->assertSession()->elementExists('xpath', $this->assertSession()->buildXPathQuery('//table/tbody/tr/td/a[contains(@href, :href) and contains(@title, :title) and text()=:text]', [
+      ':href' => $comments[0]->permalink()->toString(),
+      ':title' => Unicode::truncate($comments[0]->get('comment_body')->value, 128),
+      ':text' => $comments[0]->getSubject(),
+    ]));
+
+    // Verify that anonymous author name is displayed correctly.
+    $this->assertSession()->pageTextContains($author_name . ' (not verified)');
+
+    // Test that comment listing shows the correct subject link.
+    $this->assertSession()->elementExists('xpath', $this->assertSession()->buildXPathQuery('//table/tbody/tr/td/a[contains(@href, :href) and contains(@title, :title) and text()=:text]', [
+      ':href' => $anonymous_comment4->permalink()->toString(),
+      ':title' => Unicode::truncate($body, 128),
+      ':text' => $subject,
+    ]));
+
+    // Verify that anonymous author name is displayed correctly.
+    $this->assertSession()->pageTextContains($author_name . ' (not verified)');
+
+    // Delete multiple comments in one operation.
+    $edit = [
+      'action' => 'comment_delete_action',
+      "comment_bulk_form[1]" => $comments[0]->id(),
+      "comment_bulk_form[0]" => $comments[1]->id(),
+      "comment_bulk_form[2]" => $anonymous_comment4->id(),
+    ];
+    $this->submitForm($edit, 'Apply to selected items');
+    $this->assertSession()->pageTextContains('Are you sure you want to delete these comments and all their children?');
+    $this->submitForm([], 'Delete');
+    $this->assertSession()->pageTextContains('No comments available.');
+
+    // Make sure the label of unpublished node is not visible on listing page.
+    $this->drupalGet('admin/content/comment');
+    $this->postComment($this->node, $this->randomMachineName());
+    $this->drupalLogout();
+    $this->drupalLogin($this->adminUser);
+    $this->drupalGet('admin/content/comment');
+    // Verify that comment admin can see the title of a published node.
+    $this->assertSession()->pageTextContains(Html::escape($this->node->label()));
+    $this->node->setUnpublished()->save();
+    $this->assertFalse($this->node->isPublished(), 'Node is unpublished now.');
+    $this->drupalGet('admin/content/comment');
+    // Verify that comment admin cannot see the title of an unpublished node.
+    $this->assertSession()->pageTextNotContains(Html::escape($this->node->label()));
+    $this->drupalLogout();
+    $node_access_user = $this->drupalCreateUser([
+      'administer comments',
+      'bypass node access',
+    ]);
+    $this->drupalLogin($node_access_user);
+    $this->drupalGet('admin/content/comment');
+    // Verify that comment admin with bypass node access permissions can still
+    // see the title of a published node.
+    $this->assertSession()->pageTextContains(Html::escape($this->node->label()));
+  }
+
+  /**
+   * Tests commented entity label of admin view.
+   */
+  public function testCommentedEntityLabel(): void {
+    \Drupal::service('module_installer')->install(['block_content']);
+    \Drupal::service('router.builder')->rebuildIfNeeded();
+    $bundle = BlockContentType::create([
+      'id' => 'basic',
+      'label' => 'basic',
+      'revision' => FALSE,
+    ]);
+    $bundle->save();
+    $block_content = BlockContent::create([
+      'type' => 'basic',
+      'label' => 'Some block title',
+      'info' => 'Test block',
+    ]);
+    $block_content->save();
+
+    // Create comment field on block_content.
+    $this->addDefaultCommentField('block_content', 'basic', 'block_comment', CommentItemInterface::OPEN, 'block_comment');
+    $this->drupalLogin($this->webUser);
+    // Post a comment to node.
+    $node_comment = $this->postComment($this->node, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+    // Post a comment to block content.
+    $block_content_comment = $this->postComment($block_content, $this->randomMachineName(), $this->randomMachineName(), TRUE, 'block_comment');
+    $this->drupalLogout();
+    // Login as admin to test the admin comment page.
+    $this->drupalLogin($this->adminUser);
+    $this->drupalGet('admin/content/comment');
+
+    // Test that comment listing links to comment author.
+    $this->assertSession()->elementExists('xpath', $this->assertSession()->buildXPathQuery('//table/tbody/tr[1]/td/a[contains(@href, :href) and text()=:text]', [
+      ':href' => $this->webUser->toUrl()->toString(),
+      ':text' => $this->webUser->label(),
+    ]));
+    $this->assertSession()->elementExists('xpath', $this->assertSession()->buildXPathQuery('//table/tbody/tr[2]/td/a[contains(@href, :href) and text()=:text]', [
+      ':href' => $this->webUser->toUrl()->toString(),
+      ':text' => $this->webUser->label(),
+    ]));
+
+    // Admin page contains label of both entities.
+    $this->assertSession()->pageTextContains(Html::escape($this->node->label()));
+    $this->assertSession()->pageTextContains(Html::escape($block_content->label()));
+    // Admin page contains subject of both entities.
+    $this->assertSession()->pageTextContains(Html::escape($node_comment->label()));
+    $this->assertSession()->pageTextContains(Html::escape($block_content_comment->label()));
+  }
+
+}

core/modules/comment/tests/src/Functional/Views/CommentApproveLinkTest.php

@@ -0,0 +1,61 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional\Views;
+
+/**
+ * Test the "approve_comment" views field for approving comments.
+ *
+ * @group comment
+ */
+class CommentApproveLinkTest extends CommentTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'comment',
+    'comment_test_views',
+    'system',
+    'views',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Views used by this test.
+   *
+   * @var array
+   */
+  public static $testViews = ['test_comment_schema'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp($import_test_views = TRUE, $modules = ['comment_test_views']): void {
+    parent::setUp($import_test_views, $modules);
+  }
+
+  /**
+   * Tests that "approve comment" link exists and works as expected.
+   */
+  public function testCommentApproveLink(): void {
+    $this->drupalLogin($this->drupalCreateUser(['administer comments']));
+    // Set the comment status to unpublished.
+    $this->comment->setUnpublished();
+    $this->comment->save();
+    $this->drupalGet('/admin/moderate-comments');
+    $this->assertSession()->pageTextContains($this->comment->getSubject());
+    $this->assertSession()->linkExists('Approve');
+    $this->clickLink('Approve');
+    $this->drupalGet('/admin/moderate-comments');
+    $this->assertSession()->linkNotExists('Approve');
+    // Ensure that "published" column in table is marked as yes.
+    $this->assertSession()->elementTextContains('xpath', "//table/tbody/tr/td[3]", 'Yes');
+  }
+
+}

core/modules/comment/tests/src/Functional/Views/CommentEditTest.php

@@ -0,0 +1,39 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional\Views;
+
+use Drupal\Tests\comment\Functional\CommentTestBase as CommentBrowserTestBase;
+
+/**
+ * Tests comment edit functionality.
+ *
+ * @group comment
+ */
+class CommentEditTest extends CommentBrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Tests comment label in admin view.
+   */
+  public function testCommentEdit(): void {
+    $this->drupalLogin($this->adminUser);
+    // Post a comment to node.
+    $node_comment = $this->postComment($this->node, $this->randomMachineName(), $this->randomMachineName(), TRUE);
+    $this->drupalGet('admin/content/comment');
+    $this->assertSession()->pageTextContains($this->adminUser->label());
+    $this->drupalGet($node_comment->toUrl('edit-form'));
+    $edit = [
+      'comment_body[0][value]' => $this->randomMachineName(),
+    ];
+    $this->submitForm($edit, 'Save');
+    $this->drupalGet('admin/content/comment');
+    $this->assertSession()->pageTextContains($this->adminUser->label());
+  }
+
+}

core/modules/comment/tests/src/Functional/Views/CommentFieldFilterTest.php

@@ -0,0 +1,132 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional\Views;
+
+use Drupal\language\Entity\ConfigurableLanguage;
+use Drupal\comment\Entity\Comment;
+
+/**
+ * Tests comment field filters with translations.
+ *
+ * @group comment
+ */
+class CommentFieldFilterTest extends CommentTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['language'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Views used by this test.
+   *
+   * @var array
+   */
+  public static $testViews = ['test_field_filters'];
+
+  /**
+   * List of comment titles by language.
+   *
+   * @var array
+   */
+  public $commentTitles = [];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp($import_test_views = TRUE, $modules = ['comment_test_views']): void {
+    parent::setUp($import_test_views, $modules);
+    $this->drupalLogin($this->drupalCreateUser(['access comments']));
+
+    // Add two new languages.
+    ConfigurableLanguage::createFromLangcode('fr')->save();
+    ConfigurableLanguage::createFromLangcode('es')->save();
+
+    // Set up comment titles.
+    $this->commentTitles = [
+      'en' => 'Food in Paris',
+      'es' => 'Comida en Paris',
+      'fr' => 'Nourriture en Paris',
+    ];
+
+    // Create a new comment. Using the one created earlier will not work,
+    // as it predates the language set-up.
+    $comment = [
+      'uid' => $this->loggedInUser->id(),
+      'entity_id' => $this->nodeUserCommented->id(),
+      'entity_type' => 'node',
+      'field_name' => 'comment',
+      'cid' => '',
+      'pid' => '',
+      'node_type' => '',
+    ];
+    $this->comment = Comment::create($comment);
+
+    // Add field values and translate the comment.
+    $this->comment->subject->value = $this->commentTitles['en'];
+    $this->comment->comment_body->value = $this->commentTitles['en'];
+    $this->comment->langcode = 'en';
+    $this->comment->save();
+    foreach (['es', 'fr'] as $langcode) {
+      $translation = $this->comment->addTranslation($langcode, []);
+      $translation->comment_body->value = $this->commentTitles[$langcode];
+      $translation->subject->value = $this->commentTitles[$langcode];
+    }
+    $this->comment->save();
+  }
+
+  /**
+   * Tests body and title filters.
+   */
+  public function testFilters(): void {
+    // Test the title filter page, which filters for title contains 'Comida'.
+    // Should show just the Spanish translation, once.
+    $this->assertPageCounts('test-title-filter', ['es' => 1, 'fr' => 0, 'en' => 0], 'Comida title filter');
+
+    // Test the body filter page, which filters for body contains 'Comida'.
+    // Should show just the Spanish translation, once.
+    $this->assertPageCounts('test-body-filter', ['es' => 1, 'fr' => 0, 'en' => 0], 'Comida body filter');
+
+    // Test the title Paris filter page, which filters for title contains
+    // 'Paris'. Should show each translation once.
+    $this->assertPageCounts('test-title-paris', ['es' => 1, 'fr' => 1, 'en' => 1], 'Paris title filter');
+
+    // Test the body Paris filter page, which filters for body contains
+    // 'Paris'. Should show each translation once.
+    $this->assertPageCounts('test-body-paris', ['es' => 1, 'fr' => 1, 'en' => 1], 'Paris body filter');
+  }
+
+  /**
+   * Asserts that the given comment translation counts are correct.
+   *
+   * @param string $path
+   *   Path of the page to test.
+   * @param array $counts
+   *   Array whose keys are languages, and values are the number of times
+   *   that translation should be shown on the given page.
+   * @param string $message
+   *   Message suffix to display.
+   *
+   * @internal
+   */
+  protected function assertPageCounts(string $path, array $counts, string $message): void {
+    // Get the text of the page.
+    $this->drupalGet($path);
+    $text = $this->getTextContent();
+
+    // Check the counts. Note that the title and body are both shown on the
+    // page, and they are the same. So the title/body string should appear on
+    // the page twice as many times as the input count.
+    foreach ($counts as $langcode => $count) {
+      $this->assertEquals(2 * $count, substr_count($text, $this->commentTitles[$langcode]), 'Translation ' . $langcode . ' has count ' . $count . ' with ' . $message);
+    }
+  }
+
+}

core/modules/comment/tests/src/Functional/Views/CommentOperationsTest.php

@@ -0,0 +1,40 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional\Views;
+
+/**
+ * Tests comment operations.
+ *
+ * @group comment
+ */
+class CommentOperationsTest extends CommentTestBase {
+
+  /**
+   * Views used by this test.
+   *
+   * @var array
+   */
+  public static $testViews = ['test_comment_operations'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Tests the operations field plugin.
+   */
+  public function testCommentOperations(): void {
+    $admin_account = $this->drupalCreateUser(['administer comments']);
+    $this->drupalLogin($admin_account);
+    $this->drupalGet('test-comment-operations');
+    $this->assertSession()->statusCodeEquals(200);
+    // Assert Edit operation is present.
+    $this->assertSession()->elementsCount('xpath', '//td[contains(@class, "views-field-operations")]//li/a[text() = "Edit"]', 1);
+    // Assert Delete operation is present.
+    $this->assertSession()->elementsCount('xpath', '//td[contains(@class, "views-field-operations")]//li/a[text() = "Delete"]', 1);
+  }
+
+}

core/modules/comment/tests/src/Functional/Views/CommentRowTest.php

@@ -0,0 +1,34 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional\Views;
+
+/**
+ * Tests the comment row plugin.
+ *
+ * @group comment
+ */
+class CommentRowTest extends CommentTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Views used by this test.
+   *
+   * @var array
+   */
+  public static $testViews = ['test_comment_row'];
+
+  /**
+   * Tests comment row.
+   */
+  public function testCommentRow(): void {
+    $this->drupalGet('test-comment-row');
+    $this->assertSession()->elementsCount('xpath', '//article[contains(@class, "comment")]', 1);
+  }
+
+}

core/modules/comment/tests/src/Functional/Views/CommentTestBase.php

@@ -0,0 +1,92 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional\Views;
+
+use Drupal\comment\Tests\CommentTestTrait;
+use Drupal\Tests\views\Functional\ViewTestBase;
+use Drupal\comment\Entity\Comment;
+
+/**
+ * Provides setup and helper methods for comment views tests.
+ */
+abstract class CommentTestBase extends ViewTestBase {
+
+  use CommentTestTrait;
+
+  /**
+   * Modules to install.
+   *
+   * @var array
+   */
+  protected static $modules = ['node', 'comment', 'comment_test_views'];
+
+  /**
+   * A normal user with permission to post comments (without approval).
+   *
+   * @var \Drupal\user\UserInterface
+   */
+  protected $account;
+
+  /**
+   * A second normal user that will author a node for $account to comment on.
+   *
+   * @var \Drupal\user\UserInterface
+   */
+  protected $account2;
+
+  /**
+   * Stores a node posted by the user created as $account.
+   *
+   * @var \Drupal\node\NodeInterface
+   */
+  protected $nodeUserPosted;
+
+  /**
+   * Stores a node posted by the user created as $account2.
+   *
+   * @var \Drupal\node\NodeInterface
+   */
+  protected $nodeUserCommented;
+
+  /**
+   * Stores a comment used by the tests.
+   *
+   * @var \Drupal\comment\Entity\Comment
+   */
+  protected $comment;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp($import_test_views = TRUE, $modules = ['comment_test_views']): void {
+    parent::setUp($import_test_views, $modules);
+
+    // Add two users, create a node with the user1 as author and another node
+    // with user2 as author. For the second node add a comment from user1.
+    $this->account = $this->drupalCreateUser(['skip comment approval']);
+    $this->account2 = $this->drupalCreateUser();
+    $this->drupalLogin($this->account);
+
+    $this->drupalCreateContentType(['type' => 'page', 'name' => t('Basic page')]);
+    $this->addDefaultCommentField('node', 'page');
+
+    $this->nodeUserPosted = $this->drupalCreateNode();
+    $this->nodeUserCommented = $this->drupalCreateNode(['uid' => $this->account2->id()]);
+
+    $comment = [
+      'uid' => $this->loggedInUser->id(),
+      'entity_id' => $this->nodeUserCommented->id(),
+      'entity_type' => 'node',
+      'field_name' => 'comment',
+      'subject' => 'How much wood would a woodchuck chuck',
+      'cid' => '',
+      'pid' => '',
+      'mail' => 'someone@example.com',
+    ];
+    $this->comment = Comment::create($comment);
+    $this->comment->save();
+  }
+
+}

core/modules/comment/tests/src/Functional/Views/DefaultViewRecentCommentsTest.php

@@ -0,0 +1,148 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional\Views;
+
+use Drupal\comment\CommentInterface;
+use Drupal\comment\Entity\Comment;
+use Drupal\comment\Tests\CommentTestTrait;
+use Drupal\views\Views;
+use Drupal\Tests\views\Functional\ViewTestBase;
+
+/**
+ * Tests results for the Recent Comments view shipped with the module.
+ *
+ * @group comment
+ */
+class DefaultViewRecentCommentsTest extends ViewTestBase {
+
+  use CommentTestTrait;
+
+  /**
+   * Modules to install.
+   *
+   * @var array
+   */
+  protected static $modules = ['node', 'comment', 'block'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Number of results for the Default display.
+   *
+   * @var int
+   */
+  protected $defaultDisplayResults = 5;
+
+  /**
+   * Number of results for the Block display.
+   *
+   * @var int
+   */
+  protected $blockDisplayResults = 5;
+
+  /**
+   * Number of results for the Page display.
+   *
+   * @var int
+   */
+  protected $pageDisplayResults = 5;
+
+  /**
+   * Will hold the comments created for testing.
+   *
+   * @var array
+   */
+  protected $commentsCreated = [];
+
+  /**
+   * Contains the node object used for comments of this test.
+   *
+   * @var \Drupal\node\NodeInterface
+   */
+  public $node;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp($import_test_views = TRUE, $modules = []): void {
+    parent::setUp($import_test_views, $modules);
+
+    // Create a new content type
+    $content_type = $this->drupalCreateContentType();
+
+    // Add a node of the new content type.
+    $node_data = [
+      'type' => $content_type->id(),
+    ];
+
+    $this->addDefaultCommentField('node', $content_type->id());
+    $this->node = $this->drupalCreateNode($node_data);
+
+    // Force a flush of the in-memory storage.
+    $this->container->get('views.views_data')->clear();
+
+    // Create some comments and attach them to the created node.
+    for ($i = 0; $i < $this->defaultDisplayResults; $i++) {
+      /** @var \Drupal\comment\CommentInterface $comment */
+      $comment = Comment::create([
+        'status' => CommentInterface::PUBLISHED,
+        'field_name' => 'comment',
+        'entity_type' => 'node',
+        'entity_id' => $this->node->id(),
+      ]);
+      $comment->setOwnerId(0);
+      $comment->setSubject('Test comment ' . $i);
+      $comment->comment_body->value = 'Test body ' . $i;
+      $comment->comment_body->format = 'full_html';
+
+      // Ensure comments are sorted in ascending order.
+      $time = \Drupal::time()->getRequestTime() + ($this->defaultDisplayResults - $i);
+      $comment->setCreatedTime($time);
+      $comment->changed->value = $time;
+
+      $comment->save();
+    }
+
+    // Store all the nodes just created to access their properties on the tests.
+    $this->commentsCreated = Comment::loadMultiple();
+
+    // Sort created comments in descending order.
+    ksort($this->commentsCreated, SORT_NUMERIC);
+  }
+
+  /**
+   * Tests the block defined by the comments_recent view.
+   */
+  public function testBlockDisplay(): void {
+    $user = $this->drupalCreateUser(['access comments']);
+    $this->drupalLogin($user);
+
+    $view = Views::getView('comments_recent');
+    $view->setDisplay('block_1');
+    $this->executeView($view);
+
+    $map = [
+      'subject' => 'subject',
+      'cid' => 'cid',
+      'comment_field_data_created' => 'created',
+    ];
+    $expected_result = [];
+    foreach (array_values($this->commentsCreated) as $key => $comment) {
+      $expected_result[$key]['subject'] = $comment->getSubject();
+      $expected_result[$key]['cid'] = $comment->id();
+      $expected_result[$key]['created'] = $comment->getCreatedTime();
+    }
+    $this->assertIdenticalResultset($view, $expected_result, $map);
+
+    // Check the number of results given by the display is the expected.
+    $this->assertCount($this->blockDisplayResults, $view->result,
+      'There are exactly ' . count($view->result) . ' comments. Expected ' . $this->blockDisplayResults
+    );
+  }
+
+}

core/modules/comment/tests/src/Functional/Views/NodeCommentsTest.php

@@ -0,0 +1,69 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional\Views;
+
+/**
+ * Tests comments on nodes.
+ *
+ * @group comment
+ */
+class NodeCommentsTest extends CommentTestBase {
+
+  /**
+   * Modules to install.
+   *
+   * @var array
+   */
+  protected static $modules = ['history'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Views used by this test.
+   *
+   * @var array
+   */
+  public static $testViews = ['test_new_comments', 'test_comment_count'];
+
+  /**
+   * Tests the new comments field plugin.
+   */
+  public function testNewComments(): void {
+    $this->drupalGet('test-new-comments');
+    $this->assertSession()->statusCodeEquals(200);
+    $new_comments = $this->cssSelect(".views-field-new-comments a:contains('1')");
+    $this->assertCount(1, $new_comments, 'Found the number of new comments for a certain node.');
+  }
+
+  /**
+   * Test the comment count field.
+   */
+  public function testCommentCount(): void {
+    $this->drupalGet('test-comment-count');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertCount(2, $this->cssSelect('.views-row'));
+    $comment_count_with_comment = $this->cssSelect(".views-field-comment-count span:contains('1')");
+    $this->assertCount(1, $comment_count_with_comment);
+    $comment_count_without_comment = $this->cssSelect(".views-field-comment-count span:contains('0')");
+    $this->assertCount(1, $comment_count_without_comment);
+
+    // Create a content type with no comment field, and add a node.
+    $this->drupalCreateContentType(['type' => 'no_comment', 'name' => 'No comment page']);
+    $this->nodeUserPosted = $this->drupalCreateNode(['type' => 'no_comment']);
+    $this->drupalGet('test-comment-count');
+
+    // Test that the node with no comment field is also shown.
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertCount(3, $this->cssSelect('.views-row'));
+    $comment_count_with_comment = $this->cssSelect(".views-field-comment-count span:contains('1')");
+    $this->assertCount(1, $comment_count_with_comment);
+    $comment_count_without_comment = $this->cssSelect(".views-field-comment-count span:contains('0')");
+    $this->assertCount(2, $comment_count_without_comment);
+  }
+
+}

core/modules/comment/tests/src/Functional/Views/RowRssTest.php

@@ -0,0 +1,41 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional\Views;
+
+/**
+ * Tests the comment rss row plugin.
+ *
+ * @group comment
+ * @see \Drupal\comment\Plugin\views\row\Rss
+ */
+class RowRssTest extends CommentTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Views used by this test.
+   *
+   * @var array
+   */
+  public static $testViews = ['test_comment_rss'];
+
+  /**
+   * Tests comment rss output.
+   */
+  public function testRssRow(): void {
+    $this->drupalGet('test-comment-rss');
+
+    // Because the response is XML we can't use the page which depends on an
+    // HTML tag being present.
+    $result = $this->getSession()->getDriver()->find('//item');
+    $this->assertCount(1, $result, 'Just one comment was found in the rss output.');
+
+    $this->assertEquals(gmdate('r', $this->comment->getCreatedTime()), $result[0]->find('xpath', '//pubDate')->getHtml(), 'The right pubDate appears in the rss output.');
+  }
+
+}

core/modules/comment/tests/src/Functional/Views/WizardTest.php

@@ -0,0 +1,105 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Functional\Views;
+
+use Drupal\comment\Tests\CommentTestTrait;
+use Drupal\views\Views;
+use Drupal\Tests\views\Functional\Wizard\WizardTestBase;
+
+/**
+ * Tests the comment module integration into the wizard.
+ *
+ * @group comment
+ * @see \Drupal\comment\Plugin\views\wizard\Comment
+ */
+class WizardTest extends WizardTestBase {
+
+  use CommentTestTrait;
+
+  /**
+   * Modules to install.
+   *
+   * @var array
+   */
+  protected static $modules = ['node', 'comment'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp($import_test_views = TRUE, $modules = []): void {
+    parent::setUp($import_test_views, $modules);
+    $this->drupalCreateContentType(['type' => 'page', 'name' => 'Basic page']);
+    // Add comment field to page node type.
+    $this->addDefaultCommentField('node', 'page');
+  }
+
+  /**
+   * Tests adding a view of comments.
+   */
+  public function testCommentWizard(): void {
+    $view = [];
+    $view['label'] = $this->randomMachineName(16);
+    $view['id'] = $this->randomMachineName(16);
+    $view['show[wizard_key]'] = 'comment';
+    $view['page[create]'] = TRUE;
+    $view['page[path]'] = $this->randomMachineName(16);
+
+    // Just triggering the saving should automatically choose a proper row
+    // plugin.
+    $this->drupalGet('admin/structure/views/add');
+    $this->submitForm($view, 'Save and edit');
+    // Verify that the view saving was successful and the browser got redirected
+    // to the edit page.
+    $this->assertSession()->addressEquals('admin/structure/views/view/' . $view['id']);
+
+    // If we update the type first we should get a selection of comment valid
+    // row plugins as the select field.
+
+    $this->drupalGet('admin/structure/views/add');
+    $this->drupalGet('admin/structure/views/add');
+    $this->submitForm($view, 'Update "of type" choice');
+
+    // Check for available options of the row plugin.
+    $expected_options = ['entity:comment', 'fields'];
+    $items = $this->getSession()->getPage()->findField('page[style][row_plugin]')->findAll('xpath', 'option');
+    $actual_options = [];
+    foreach ($items as $item) {
+      $actual_options[] = $item->getValue();
+    }
+    $this->assertEquals($expected_options, $actual_options);
+
+    $view['id'] = $this->randomMachineName(16);
+    $this->submitForm($view, 'Save and edit');
+    // Verify that the view saving was successful and the browser got redirected
+    // to the edit page.
+    $this->assertSession()->addressEquals('admin/structure/views/view/' . $view['id']);
+
+    $user = $this->drupalCreateUser(['access comments']);
+    $this->drupalLogin($user);
+
+    $view = Views::getView($view['id']);
+    $view->initHandlers();
+    $row = $view->display_handler->getOption('row');
+    $this->assertEquals('entity:comment', $row['type']);
+
+    // Check for the default filters.
+    $this->assertEquals('comment_field_data', $view->filter['status']->table);
+    $this->assertEquals('status', $view->filter['status']->field);
+    $this->assertEquals('1', $view->filter['status']->value);
+    $this->assertEquals('node_field_data', $view->filter['status_node']->table);
+    $this->assertEquals('status', $view->filter['status_node']->field);
+    $this->assertEquals('1', $view->filter['status_node']->value);
+
+    // Check for the default fields.
+    $this->assertEquals('comment_field_data', $view->field['subject']->table);
+    $this->assertEquals('subject', $view->field['subject']->field);
+  }
+
+}

core/modules/comment/tests/src/Kernel/CommentBaseFieldTest.php

@@ -0,0 +1,68 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Kernel;
+
+use Drupal\comment\CommentInterface;
+use Drupal\comment\Entity\Comment;
+use Drupal\comment\Plugin\Field\FieldType\CommentItemInterface;
+use Drupal\comment_base_field_test\Entity\CommentTestBaseField;
+use Drupal\Core\Language\LanguageInterface;
+use Drupal\KernelTests\KernelTestBase;
+
+/**
+ * Tests that comment as a base field.
+ *
+ * @group comment
+ */
+class CommentBaseFieldTest extends KernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'system',
+    'user',
+    'comment',
+    'comment_base_field_test',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->installEntitySchema('comment_test_base_field');
+    $this->installEntitySchema('comment');
+    $this->installEntitySchema('user');
+  }
+
+  /**
+   * Tests comment as a base field.
+   */
+  public function testCommentBaseField(): void {
+    // Verify entity creation.
+    $entity = CommentTestBaseField::create([
+      'name' => $this->randomMachineName(),
+      'test_comment' => CommentItemInterface::OPEN,
+    ]);
+    $entity->save();
+
+    $comment = Comment::create([
+      'entity_id' => $entity->id(),
+      'entity_type' => 'comment_test_base_field',
+      'field_name' => 'test_comment',
+      'pid' => 0,
+      'uid' => 0,
+      'status' => CommentInterface::PUBLISHED,
+      'subject' => $this->randomMachineName(),
+      'hostname' => '127.0.0.1',
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
+      'comment_body' => [['value' => $this->randomMachineName()]],
+    ]);
+    $comment->save();
+    $this->assertEquals('test_comment_type', $comment->bundle());
+  }
+
+}

core/modules/comment/tests/src/Kernel/CommentBundlesTest.php

@@ -0,0 +1,85 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Kernel;
+
+use Drupal\comment\Entity\CommentType;
+use Drupal\KernelTests\KernelTestBase;
+
+/**
+ * Tests that comment bundles behave as expected.
+ *
+ * @group comment
+ */
+class CommentBundlesTest extends KernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['comment', 'node', 'taxonomy', 'user'];
+
+  /**
+   * Entity type ids to use for target_entity_type_id on comment bundles.
+   *
+   * @var array
+   */
+  protected $targetEntityTypes;
+
+  /**
+   * @var \Drupal\Core\Entity\EntityFieldManagerInterface
+   */
+  protected $entityFieldManager;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->entityFieldManager = $this->container->get('entity_field.manager');
+
+    $this->installEntitySchema('comment');
+
+    // Create multiple comment bundles,
+    // each of which has a different target entity type.
+    $this->targetEntityTypes = [
+      'comment' => 'Comment',
+      'node' => 'Node',
+      'taxonomy_term' => 'Taxonomy Term',
+    ];
+    foreach ($this->targetEntityTypes as $id => $label) {
+      CommentType::create([
+        'id' => 'comment_on_' . $id,
+        'label' => 'Comment on ' . $label,
+        'target_entity_type_id' => $id,
+      ])->save();
+    }
+  }
+
+  /**
+   * Tests that the entity_id field is set correctly for each comment bundle.
+   */
+  public function testEntityIdField(): void {
+    $field_definitions = [];
+
+    foreach (array_keys($this->targetEntityTypes) as $id) {
+      $bundle = 'comment_on_' . $id;
+      $field_definitions[$bundle] = $this->entityFieldManager
+        ->getFieldDefinitions('comment', $bundle);
+    }
+    // Test that the value of the entity_id field for each bundle is correct.
+    foreach ($field_definitions as $bundle => $definition) {
+      $entity_type_id = str_replace('comment_on_', '', $bundle);
+      $target_type = $definition['entity_id']->getSetting('target_type');
+      $this->assertEquals($entity_type_id, $target_type);
+
+      // Verify that the target type remains correct
+      // in the deeply-nested object properties.
+      $nested_target_type = $definition['entity_id']->getItemDefinition()->getFieldDefinition()->getSetting('target_type');
+      $this->assertEquals($entity_type_id, $nested_target_type);
+    }
+
+  }
+
+}

core/modules/comment/tests/src/Kernel/CommentDefaultFormatterCacheTagsTest.php

@@ -0,0 +1,166 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Kernel;
+
+use Drupal\comment\Tests\CommentTestTrait;
+use Drupal\Core\Cache\Cache;
+use Drupal\comment\CommentInterface;
+use Drupal\KernelTests\Core\Entity\EntityKernelTestBase;
+use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\HttpFoundation\Session\Session;
+use Drupal\comment\Entity\Comment;
+use Drupal\entity_test\Entity\EntityTest;
+
+/**
+ * Tests comment cache tag bubbling up when using the Comment list formatter.
+ *
+ * @group comment
+ */
+class CommentDefaultFormatterCacheTagsTest extends EntityKernelTestBase {
+
+  use CommentTestTrait;
+
+  /**
+   * Modules to install.
+   *
+   * @var array
+   */
+  protected static $modules = ['entity_test', 'comment'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // Create user 1 so that the user created later in the test has a different
+    // user ID.
+    // @todo Remove in https://www.drupal.org/node/540008.
+    $this->createUser([], NULL, FALSE, ['uid' => 1, 'name' => 'user1'])->save();
+
+    $this->container->get('module_handler')->loadInclude('comment', 'install');
+    comment_install();
+
+    $session = new Session();
+
+    $request = Request::create('/');
+    $request->setSession($session);
+
+    /** @var \Symfony\Component\HttpFoundation\RequestStack $stack */
+    $stack = $this->container->get('request_stack');
+    $stack->pop();
+    $stack->push($request);
+
+    // Set the current user to one that can access comments. Specifically, this
+    // user does not have access to the 'administer comments' permission, to
+    // ensure only published comments are visible to the end user.
+    $current_user = $this->container->get('current_user');
+    $current_user->setAccount($this->createUser(['access comments', 'post comments']));
+
+    // Install tables and config needed to render comments.
+    $this->installSchema('comment', ['comment_entity_statistics']);
+    $this->installConfig(['system', 'filter', 'comment']);
+
+    // Set up a field, so that the entity that'll be referenced bubbles up a
+    // cache tag when rendering it entirely.
+    $this->addDefaultCommentField('entity_test', 'entity_test');
+  }
+
+  /**
+   * Tests the bubbling of cache tags.
+   */
+  public function testCacheTags(): void {
+    /** @var \Drupal\Core\Render\RendererInterface $renderer */
+    $renderer = $this->container->get('renderer');
+
+    // Create the entity that will be commented upon.
+    $commented_entity = EntityTest::create(['name' => $this->randomMachineName()]);
+    $commented_entity->save();
+
+    // Verify cache tags on the rendered entity before it has comments.
+    $build = \Drupal::entityTypeManager()
+      ->getViewBuilder('entity_test')
+      ->view($commented_entity);
+    $renderer->renderRoot($build);
+    $expected_cache_tags = [
+      'entity_test_view',
+      'CACHE_MISS_IF_UNCACHEABLE_HTTP_METHOD:form',
+      'entity_test:' . $commented_entity->id(),
+      'config:core.entity_form_display.comment.comment.default',
+      'config:field.field.comment.comment.comment_body',
+      'config:field.field.entity_test.entity_test.comment',
+      'config:field.storage.comment.comment_body',
+      'config:user.settings',
+    ];
+    $this->assertEqualsCanonicalizing($expected_cache_tags, $build['#cache']['tags']);
+
+    // Create a comment on that entity. Comment loading requires that the uid
+    // also exists in the {users} table.
+    $user = $this->createUser();
+    $user->save();
+    $comment = Comment::create([
+      'subject' => 'Llama',
+      'comment_body' => [
+        'value' => 'Llamas are cool!',
+        'format' => 'plain_text',
+      ],
+      'entity_id' => $commented_entity->id(),
+      'entity_type' => 'entity_test',
+      'field_name' => 'comment',
+      'comment_type' => 'comment',
+      'status' => CommentInterface::PUBLISHED,
+      'uid' => $user->id(),
+    ]);
+    $comment->save();
+
+    // Load commented entity so comment_count gets computed.
+    // @todo Remove the $reset = TRUE parameter after
+    //   https://www.drupal.org/node/597236 lands. It's a temporary work-around.
+    $storage = $this->container->get('entity_type.manager')->getStorage('entity_test');
+    $storage->resetCache([$commented_entity->id()]);
+    $commented_entity = $storage->load($commented_entity->id());
+
+    // Verify cache tags on the rendered entity when it has comments.
+    $build = \Drupal::entityTypeManager()
+      ->getViewBuilder('entity_test')
+      ->view($commented_entity);
+    $renderer->renderRoot($build);
+    $expected_cache_tags = [
+      'entity_test_view',
+      'entity_test:' . $commented_entity->id(),
+      'comment_view',
+      'comment:' . $comment->id(),
+      'config:filter.format.plain_text',
+      'user_view',
+      'CACHE_MISS_IF_UNCACHEABLE_HTTP_METHOD:form',
+      'user:' . $user->id(),
+      'config:core.entity_form_display.comment.comment.default',
+      'config:field.field.comment.comment.comment_body',
+      'config:field.field.entity_test.entity_test.comment',
+      'config:field.storage.comment.comment_body',
+      'config:user.settings',
+    ];
+    $this->assertEqualsCanonicalizing($expected_cache_tags, $build['#cache']['tags']);
+
+    // Build a render array with the entity in a sub-element so that lazy
+    // builder elements bubble up outside of the entity and we can check that
+    // it got the correct cache max age.
+    $build = ['#type' => 'container'];
+    $build['entity'] = \Drupal::entityTypeManager()
+      ->getViewBuilder('entity_test')
+      ->view($commented_entity);
+    $renderer->renderRoot($build);
+
+    // The entity itself was cached but the top-level element is max-age 0 due
+    // to the bubbled up max age due to the lazy-built comment form.
+    $this->assertSame(Cache::PERMANENT, $build['entity']['#cache']['max-age']);
+    $this->assertSame(0, $build['#cache']['max-age'], 'Top level render array has max-age 0');
+
+    // The children (fields) of the entity render array are only built in case
+    // of a cache miss.
+    $this->assertFalse(isset($build['entity']['comment']), 'Cache hit');
+  }
+
+}

core/modules/comment/tests/src/Kernel/CommentFieldAccessTest.php

@@ -0,0 +1,357 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Kernel;
+
+use Drupal\comment\CommentInterface;
+use Drupal\comment\Entity\Comment;
+use Drupal\comment\Entity\CommentType;
+use Drupal\comment\Plugin\Field\FieldType\CommentItemInterface;
+use Drupal\comment\Tests\CommentTestTrait;
+use Drupal\Core\Session\AnonymousUserSession;
+use Drupal\entity_test\Entity\EntityTest;
+use Drupal\field\Entity\FieldConfig;
+use Drupal\KernelTests\Core\Entity\EntityKernelTestBase;
+use Drupal\Tests\Traits\Core\GeneratePermutationsTrait;
+use Drupal\user\Entity\Role;
+use Drupal\user\RoleInterface;
+
+/**
+ * Tests comment field level access.
+ *
+ * @group comment
+ * @group Access
+ */
+class CommentFieldAccessTest extends EntityKernelTestBase {
+
+  use CommentTestTrait;
+  use GeneratePermutationsTrait;
+
+  /**
+   * Modules to install.
+   *
+   * @var array
+   */
+  protected static $modules = ['comment', 'entity_test', 'user'];
+
+  /**
+   * Fields that only users with administer comments permissions can change.
+   *
+   * @var array
+   */
+  protected $administrativeFields = [
+    'uid',
+    'status',
+    'created',
+  ];
+
+  /**
+   * These fields are automatically managed and can not be changed by any user.
+   *
+   * @var array
+   */
+  protected $readOnlyFields = [
+    'changed',
+    'hostname',
+    'cid',
+    'thread',
+  ];
+
+  /**
+   * These fields can be edited on create only.
+   *
+   * @var array
+   */
+  protected $createOnlyFields = [
+    'uuid',
+    'pid',
+    'comment_type',
+    'entity_id',
+    'entity_type',
+    'field_name',
+  ];
+
+  /**
+   * These fields can only be edited by the admin or anonymous users if allowed.
+   *
+   * @var array
+   */
+  protected $contactFields = [
+    'name',
+    'mail',
+    'homepage',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->installConfig(['user', 'comment']);
+    $this->installSchema('comment', ['comment_entity_statistics']);
+  }
+
+  /**
+   * Tests permissions on comment fields.
+   */
+  public function testAccessToAdministrativeFields(): void {
+    // Create a comment type.
+    $comment_type = CommentType::create([
+      'id' => 'comment',
+      'label' => 'Default comments',
+      'description' => 'Default comment field',
+      'target_entity_type_id' => 'entity_test',
+    ]);
+    $comment_type->save();
+
+    // An administrator user. No user exists yet, ensure that the first user
+    // does not have UID 1.
+    $comment_admin_user = $this->createUser([
+      'administer comments',
+      'access comments',
+    ], 'admin', FALSE, ['uid' => 2]);
+
+    // Two comment enabled users, one with edit access.
+    $comment_enabled_user = $this->createUser([
+      'post comments',
+      'skip comment approval',
+      'edit own comments',
+      'access comments',
+    ], 'enabled');
+
+    $comment_no_edit_user = $this->createUser([
+      'post comments',
+      'skip comment approval',
+      'access comments',
+    ], 'no edit');
+
+    // An unprivileged user.
+    $comment_disabled_user = $this->createUser(['access content'], 'disabled');
+
+    $role = Role::load(RoleInterface::ANONYMOUS_ID);
+    $role->grantPermission('post comments')
+      ->save();
+
+    $anonymous_user = new AnonymousUserSession();
+
+    // Add two fields.
+    $this->addDefaultCommentField('entity_test', 'entity_test', 'comment');
+    $this->addDefaultCommentField('entity_test', 'entity_test', 'comment_other');
+
+    // Create a comment against a test entity.
+    $host = EntityTest::create();
+    $host->save();
+
+    $host2 = EntityTest::create();
+    $host2->comment->status = CommentItemInterface::CLOSED;
+    $host2->comment_other->status = CommentItemInterface::CLOSED;
+    $host2->save();
+
+    // Change the second field's anonymous contact setting.
+    $instance = FieldConfig::loadByName('entity_test', 'entity_test', 'comment_other');
+    // Default is 'May not contact', for this field - they may contact.
+    $instance->setSetting('anonymous', CommentInterface::ANONYMOUS_MAY_CONTACT);
+    $instance->save();
+
+    // Create three "Comments". One is owned by our edit-enabled user.
+    $comment1 = Comment::create([
+      'entity_type' => 'entity_test',
+      'name' => 'Tony',
+      'hostname' => 'magic.example.com',
+      'mail' => 'tonythemagicalpony@example.com',
+      'subject' => 'Bruce the Mesopotamian moose',
+      'entity_id' => $host->id(),
+      'comment_type' => 'comment',
+      'field_name' => 'comment',
+      'pid' => 0,
+      'uid' => 0,
+      'status' => 1,
+    ]);
+    $comment1->save();
+    $comment2 = Comment::create([
+      'entity_type' => 'entity_test',
+      'hostname' => 'magic.example.com',
+      'subject' => 'Brian the messed up lion',
+      'entity_id' => $host->id(),
+      'comment_type' => 'comment',
+      'field_name' => 'comment',
+      'status' => 1,
+      'pid' => 0,
+      'uid' => $comment_enabled_user->id(),
+    ]);
+    $comment2->save();
+    $comment3 = Comment::create([
+      'entity_type' => 'entity_test',
+      'hostname' => 'magic.example.com',
+      // Unpublished.
+      'status' => 0,
+      'subject' => 'Gail the minke whale',
+      'entity_id' => $host->id(),
+      'comment_type' => 'comment',
+      'field_name' => 'comment_other',
+      'pid' => $comment2->id(),
+      'uid' => $comment_no_edit_user->id(),
+    ]);
+    $comment3->save();
+    // Note we intentionally don't save this comment so it remains 'new'.
+    $comment4 = Comment::create([
+      'entity_type' => 'entity_test',
+      'hostname' => 'magic.example.com',
+      // Unpublished.
+      'status' => 0,
+      'subject' => 'Daniel the Cocker-Spaniel',
+      'entity_id' => $host->id(),
+      'comment_type' => 'comment',
+      'field_name' => 'comment_other',
+      'pid' => 0,
+      'uid' => $anonymous_user->id(),
+    ]);
+    // Note we intentionally don't save this comment so it remains 'new'.
+    $comment5 = Comment::create([
+      'entity_type' => 'entity_test',
+      'hostname' => 'magic.example.com',
+      // Unpublished.
+      'status' => 0,
+      'subject' => 'Wally the Border Collie',
+      // This one is closed for comments.
+      'entity_id' => $host2->id(),
+      'comment_type' => 'comment',
+      'field_name' => 'comment_other',
+      'pid' => 0,
+      'uid' => $anonymous_user->id(),
+    ]);
+
+    // Generate permutations.
+    $combinations = [
+      'comment' => [$comment1, $comment2, $comment3, $comment4, $comment5],
+      'user' => [$comment_admin_user, $comment_enabled_user, $comment_no_edit_user, $comment_disabled_user, $anonymous_user],
+    ];
+    $permutations = $this->generatePermutations($combinations);
+
+    // Check access to administrative fields.
+    foreach ($this->administrativeFields as $field) {
+      foreach ($permutations as $set) {
+        $may_view = $set['comment']->{$field}->access('view', $set['user']);
+        $may_update = $set['comment']->{$field}->access('edit', $set['user']);
+        $account_name = $set['user']->getAccountName();
+        $comment_subject = $set['comment']->getSubject();
+        $this->assertTrue($may_view, "User $account_name can view field $field on comment $comment_subject");
+        $this->assertEquals(
+          $may_update,
+          $set['user']->hasPermission('administer comments'),
+          "User $account_name" . ($may_update ? 'can' : 'cannot') . "update field $field on comment $comment_subject"
+        );
+      }
+    }
+
+    // Check access to normal field.
+    foreach ($permutations as $set) {
+      $may_update = $set['comment']->access('update', $set['user']) && $set['comment']->subject->access('edit', $set['user']);
+      $this->assertEquals(
+        $may_update,
+        $set['user']->hasPermission('administer comments') || ($set['user']->hasPermission('edit own comments') && $set['user']->id() == $set['comment']->getOwnerId()),
+        sprintf('User %s %s update field subject on comment %s',
+          $set['user']->getAccountName(),
+          $may_update ? 'can' : 'cannot',
+          $set['comment']->getSubject(),
+        ),
+      );
+    }
+
+    // Check read-only fields.
+    foreach ($this->readOnlyFields as $field) {
+      // Check view operation.
+      foreach ($permutations as $set) {
+        $may_view = $set['comment']->{$field}->access('view', $set['user']);
+        $may_update = $set['comment']->{$field}->access('edit', $set['user']);
+        // Nobody has access to view the hostname field.
+        if ($field === 'hostname') {
+          $view_access = FALSE;
+          $state = 'cannot';
+        }
+        else {
+          $view_access = TRUE;
+          $state = 'can';
+        }
+        $this->assertEquals(
+          $may_view,
+          $view_access,
+          sprintf('User %s %s view field %s on comment %s',
+            $set['user']->getAccountName(),
+            $state,
+            $field,
+            $set['comment']->getSubject(),
+          ),
+        );
+        $this->assertFalse(
+          $may_update,
+          sprintf('User %s %s update field %s on comment %s',
+            $set['user']->getAccountName(),
+            $may_update ? 'can' : 'cannot',
+            $field,
+            $set['comment']->getSubject(),
+          ),
+        );
+      }
+    }
+
+    // Check create-only fields.
+    foreach ($this->createOnlyFields as $field) {
+      // Check view operation.
+      foreach ($permutations as $set) {
+        $may_view = $set['comment']->{$field}->access('view', $set['user']);
+        $may_update = $set['comment']->{$field}->access('edit', $set['user']);
+        $this->assertTrue(
+          $may_view,
+          sprintf('User %s can view field %s on comment %s',
+            $set['user']->getAccountName(),
+            $field,
+            $set['comment']->getSubject(),
+          ),
+        );
+        $expected = $set['user']->hasPermission('post comments') && $set['comment']->isNew() && (int) $set['comment']->getCommentedEntity()->get($set['comment']->getFieldName())->status !== CommentItemInterface::CLOSED;
+        $this->assertEquals(
+          $expected,
+          $may_update,
+          sprintf('User %s %s update field %s on comment %s',
+            $set['user']->getAccountName(),
+            $expected ? 'can' : 'cannot',
+            $field,
+            $set['comment']->getSubject(),
+          ),
+        );
+      }
+    }
+
+    // Check contact fields.
+    foreach ($this->contactFields as $field) {
+      // Check view operation.
+      foreach ($permutations as $set) {
+        $may_update = $set['comment']->{$field}->access('edit', $set['user']);
+        // To edit the 'mail' or 'name' field, either the user has the
+        // "administer comments" permissions or the user is anonymous and
+        // adding a new comment using a field that allows contact details.
+        $this->assertEquals($may_update, $set['user']->hasPermission('administer comments') || (
+            $set['user']->isAnonymous() &&
+            $set['comment']->isNew() &&
+            $set['user']->hasPermission('post comments') &&
+            $set['comment']->getFieldName() == 'comment_other'
+          ),
+          sprintf('User %s %s update field %s on comment %s',
+            $set['user']->getAccountName(),
+            $may_update ? 'can' : 'cannot',
+            $field,
+            $set['comment']->getSubject(),
+          ),
+        );
+      }
+    }
+    foreach ($permutations as $set) {
+      // Check no view-access to mail field for other than admin.
+      $may_view = $set['comment']->mail->access('view', $set['user']);
+      $this->assertEquals($may_view, $set['user']->hasPermission('administer comments'));
+    }
+  }
+
+}

core/modules/comment/tests/src/Kernel/CommentHostnameTest.php

@@ -0,0 +1,60 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Kernel;
+
+use Drupal\comment\Entity\Comment;
+use Drupal\comment\Entity\CommentType;
+use Drupal\KernelTests\KernelTestBase;
+use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\HttpFoundation\Session\Session;
+use Symfony\Component\HttpFoundation\Session\Storage\MockArraySessionStorage;
+
+/**
+ * Tests the hostname base field.
+ *
+ * @coversDefaultClass \Drupal\comment\Entity\Comment
+ *
+ * @group comment
+ */
+class CommentHostnameTest extends KernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['comment', 'entity_test', 'user'];
+
+  /**
+   * Tests hostname default value callback.
+   *
+   * @covers ::getDefaultHostname
+   */
+  public function testGetDefaultHostname(): void {
+    // Create a fake request to be used for testing.
+    $request = Request::create('/', 'GET', [], [], [], ['REMOTE_ADDR' => '203.0.113.1']);
+    $request->setSession(new Session(new MockArraySessionStorage()));
+    /** @var \Symfony\Component\HttpFoundation\RequestStack $stack */
+    $stack = $this->container->get('request_stack');
+    $stack->push($request);
+
+    CommentType::create([
+      'id' => 'foo',
+      'label' => 'Foo',
+      'target_entity_type_id' => 'entity_test',
+    ])->save();
+
+    // Check that the hostname is empty by default.
+    $comment = Comment::create(['comment_type' => 'foo']);
+    $this->assertEquals('', $comment->getHostname());
+
+    \Drupal::configFactory()
+      ->getEditable('comment.settings')
+      ->set('log_ip_addresses', TRUE)
+      ->save(TRUE);
+    // Check that the hostname was set correctly.
+    $comment = Comment::create(['comment_type' => 'foo']);
+    $this->assertEquals('203.0.113.1', $comment->getHostname());
+  }
+
+}

core/modules/comment/tests/src/Kernel/CommentIntegrationTest.php

@@ -0,0 +1,168 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Kernel;
+
+use Drupal\comment\Entity\Comment;
+use Drupal\comment\Entity\CommentType;
+use Drupal\Core\Database\Database;
+use Drupal\Core\Entity\Entity\EntityViewDisplay;
+use Drupal\Core\Entity\Entity\EntityViewMode;
+use Drupal\field\Entity\FieldConfig;
+use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\KernelTests\KernelTestBase;
+use Drupal\Tests\user\Traits\UserCreationTrait;
+
+/**
+ * Tests integration of comment with other components.
+ *
+ * @group comment
+ */
+class CommentIntegrationTest extends KernelTestBase {
+
+  use UserCreationTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'comment',
+    'field',
+    'entity_test',
+    'user',
+    'system',
+    'dblog',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->installEntitySchema('entity_test');
+    $this->installEntitySchema('user');
+    $this->installEntitySchema('comment');
+    $this->installSchema('dblog', ['watchdog']);
+
+    // Create a new 'comment' comment-type.
+    CommentType::create([
+      'id' => 'comment',
+      'label' => $this->randomString(),
+      'target_entity_type_id' => 'entity_test',
+    ])->save();
+  }
+
+  /**
+   * Tests view mode setting integration.
+   *
+   * @see comment_entity_view_display_presave()
+   * @see CommentDefaultFormatter::calculateDependencies()
+   */
+  public function testViewMode(): void {
+    $mode = $this->randomMachineName();
+    // Create a new comment view mode and a view display entity.
+    EntityViewMode::create([
+      'id' => "comment.$mode",
+      'targetEntityType' => 'comment',
+      'settings' => ['comment_type' => 'comment'],
+      'label' => $mode,
+    ])->save();
+    EntityViewDisplay::create([
+      'targetEntityType' => 'comment',
+      'bundle' => 'comment',
+      'mode' => $mode,
+    ])->setStatus(TRUE)->save();
+
+    // Create a comment field attached to a host 'entity_test' entity.
+    FieldStorageConfig::create([
+      'entity_type' => 'entity_test',
+      'type' => 'comment',
+      'field_name' => $field_name = $this->randomMachineName(),
+      'settings' => [
+        'comment_type' => 'comment',
+      ],
+    ])->save();
+    FieldConfig::create([
+      'entity_type' => 'entity_test',
+      'bundle' => 'entity_test',
+      'field_name' => $field_name,
+    ])->save();
+
+    $component = [
+      'type' => 'comment_default',
+      'settings' => ['view_mode' => $mode, 'pager_id' => 0],
+    ];
+    // Create a new 'entity_test' view display on host entity that uses the
+    // custom comment display in field formatter to show the field.
+    EntityViewDisplay::create([
+      'targetEntityType' => 'entity_test',
+      'bundle' => 'entity_test',
+      'mode' => 'default',
+    ])->setComponent($field_name, $component)->setStatus(TRUE)->save();
+
+    $host_display_id = 'entity_test.entity_test.default';
+    $comment_display_id = "comment.comment.$mode";
+
+    // Disable the "comment.comment.$mode" display.
+    EntityViewDisplay::load($comment_display_id)->setStatus(FALSE)->save();
+
+    /** @var \Drupal\Core\Entity\Display\EntityViewDisplayInterface $host_display */
+    $host_display = EntityViewDisplay::load($host_display_id);
+
+    // Check that the field formatter has been disabled on host view display.
+    $this->assertNull($host_display->getComponent($field_name));
+    $this->assertTrue($host_display->get('hidden')[$field_name]);
+
+    // Check that the proper warning has been logged.
+    $arguments = [
+      '@id' => $host_display_id,
+      '@name' => $field_name,
+      '@display' => EntityViewMode::load("comment.$mode")->label(),
+      '@mode' => $mode,
+    ];
+    $logged = Database::getConnection()->select('watchdog')
+      ->fields('watchdog', ['variables'])
+      ->condition('type', 'system')
+      ->condition('message', "View display '@id': Comment field formatter '@name' was disabled because it is using the comment view display '@display' (@mode) that was just disabled.")
+      ->execute()
+      ->fetchField();
+    $this->assertEquals(serialize($arguments), $logged);
+
+    // Re-enable the comment view display.
+    EntityViewDisplay::load($comment_display_id)->setStatus(TRUE)->save();
+    // Re-enable the comment field formatter on host entity view display.
+    EntityViewDisplay::load($host_display_id)->setComponent($field_name, $component)->save();
+
+    // Delete the "comment.$mode" view mode.
+    EntityViewMode::load("comment.$mode")->delete();
+
+    // Check that the comment view display entity has been deleted too.
+    $this->assertNull(EntityViewDisplay::load($comment_display_id));
+
+    /** @var \Drupal\Core\Entity\Display\EntityViewDisplayInterface $display */
+    $host_display = EntityViewDisplay::load($host_display_id);
+
+    // Check that the field formatter has been disabled on host view display.
+    $this->assertNull($host_display->getComponent($field_name));
+    $this->assertTrue($host_display->get('hidden')[$field_name]);
+  }
+
+  /**
+   * Tests the default owner of comment entities.
+   */
+  public function testCommentDefaultOwner(): void {
+    $comment = Comment::create([
+      'comment_type' => 'comment',
+    ]);
+    $this->assertEquals(0, $comment->getOwnerId());
+
+    $user = $this->createUser();
+    $this->container->get('current_user')->setAccount($user);
+    $comment = Comment::create([
+      'comment_type' => 'comment',
+    ]);
+    $this->assertEquals($user->id(), $comment->getOwnerId());
+  }
+
+}

core/modules/comment/tests/src/Kernel/CommentItemTest.php

@@ -0,0 +1,130 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Kernel;
+
+use Drupal\comment\Entity\Comment;
+use Drupal\comment\Plugin\Field\FieldType\CommentItemInterface;
+use Drupal\comment\Tests\CommentTestTrait;
+use Drupal\Core\Field\FieldItemListInterface;
+use Drupal\entity_test\Entity\EntityTest;
+use Drupal\Tests\field\Kernel\FieldKernelTestBase;
+
+/**
+ * Tests the new entity API for the comment field type.
+ *
+ * @group comment
+ */
+class CommentItemTest extends FieldKernelTestBase {
+
+  use CommentTestTrait;
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  protected static $modules = ['comment', 'entity_test', 'user'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->installEntitySchema('comment');
+    $this->installSchema('comment', ['comment_entity_statistics']);
+    $this->installConfig(['comment']);
+  }
+
+  /**
+   * Tests using entity fields of the comment field type.
+   */
+  public function testCommentItem(): void {
+    $this->addDefaultCommentField('entity_test', 'entity_test', 'comment');
+
+    // Verify entity creation.
+    $entity = EntityTest::create();
+    $entity->name->value = $this->randomMachineName();
+    $entity->save();
+
+    // Verify entity has been created properly.
+    $id = $entity->id();
+    $storage = $this->container->get('entity_type.manager')->getStorage('entity_test');
+    $storage->resetCache([$id]);
+    $entity = $storage->load($id);
+    $this->assertInstanceOf(FieldItemListInterface::class, $entity->comment);
+    $this->assertInstanceOf(CommentItemInterface::class, $entity->comment[0]);
+
+    // Test sample item generation.
+    /** @var \Drupal\entity_test\Entity\EntityTest $entity */
+    $entity = EntityTest::create();
+    $entity->comment->generateSampleItems();
+    $this->entityValidateAndSave($entity);
+    $this->assertContains($entity->get('comment')->status, [
+      CommentItemInterface::HIDDEN,
+      CommentItemInterface::CLOSED,
+      CommentItemInterface::OPEN,
+    ], 'Comment status value in defined range');
+
+    $mainProperty = $entity->comment[0]->mainPropertyName();
+    $this->assertEquals('status', $mainProperty);
+  }
+
+  /**
+   * Tests comment author name.
+   */
+  public function testCommentAuthorName(): void {
+    $this->installEntitySchema('comment');
+    $this->addDefaultCommentField('entity_test', 'entity_test', 'comment');
+
+    $host = EntityTest::create(['name' => $this->randomString()]);
+    $host->save();
+
+    // Create some comments.
+    $comment = Comment::create([
+      'subject' => 'My comment title',
+      'uid' => 1,
+      'name' => 'entity-test',
+      'mail' => 'entity@localhost',
+      'entity_type' => 'entity_test',
+      'field_name' => 'comment',
+      'entity_id' => $host->id(),
+      'comment_type' => 'entity_test',
+      'status' => 1,
+    ]);
+    $comment->save();
+
+    // The entity fields for name and mail have no meaning if the user is not
+    // Anonymous.
+    $this->assertNull($comment->name->value);
+    $this->assertNull($comment->mail->value);
+
+    $comment_anonymous = Comment::create([
+      'subject' => 'Anonymous comment title',
+      'uid' => 0,
+      'name' => 'barry',
+      'mail' => 'test@example.com',
+      'homepage' => 'https://example.com',
+      'entity_type' => 'entity_test',
+      'field_name' => 'comment',
+      'entity_id' => $host->id(),
+      'comment_type' => 'entity_test',
+      'status' => 1,
+    ]);
+    $comment_anonymous->save();
+
+    // The entity fields for name and mail have retained their values when
+    // comment belongs to an anonymous user.
+    $this->assertNotNull($comment_anonymous->name->value);
+    $this->assertNotNull($comment_anonymous->mail->value);
+
+    $comment_anonymous->setOwnerId(1)
+      ->save();
+    // The entity fields for name and mail have no meaning if the user is not
+    // Anonymous.
+    $this->assertNull($comment_anonymous->name->value);
+    $this->assertNull($comment_anonymous->mail->value);
+  }
+
+}

core/modules/comment/tests/src/Kernel/CommentOrphanTest.php

@@ -0,0 +1,137 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Kernel;
+
+use Drupal\Core\Datetime\Entity\DateFormat;
+use Drupal\KernelTests\Core\Entity\EntityKernelTestBase;
+use Drupal\Tests\EntityViewTrait;
+use Drupal\field\Entity\FieldStorageConfig;
+
+/**
+ * Tests loading and rendering orphan comments.
+ *
+ * @group comment
+ */
+class CommentOrphanTest extends EntityKernelTestBase {
+
+  use EntityViewTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['comment', 'node', 'user'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->installConfig(['user']);
+    $this->installEntitySchema('date_format');
+    $this->installEntitySchema('comment');
+    $this->installSchema('comment', ['comment_entity_statistics']);
+  }
+
+  /**
+   * Test loading/deleting/rendering orphaned comments.
+   *
+   * @dataProvider providerTestOrphan
+   */
+  public function testOrphan($property): void {
+
+    DateFormat::create([
+      'id' => 'fallback',
+      'label' => 'Fallback',
+      'pattern' => 'Y-m-d',
+    ])->save();
+
+    $comment_storage = $this->entityTypeManager->getStorage('comment');
+    $node_storage = $this->entityTypeManager->getStorage('node');
+
+    // Create a page node type.
+    $this->entityTypeManager->getStorage('node_type')->create([
+      'type' => 'page',
+      'name' => 'page',
+    ])->save();
+
+    $node = $node_storage->create([
+      'type' => 'page',
+      'title' => 'test',
+    ]);
+    $node->save();
+
+    // Create comment field.
+    $this->entityTypeManager->getStorage('field_storage_config')->create([
+      'type' => 'text_long',
+      'entity_type' => 'node',
+      'field_name' => 'comment',
+    ])->save();
+
+    // Add comment field to page content.
+    $this->entityTypeManager->getStorage('field_config')->create([
+      'field_storage' => FieldStorageConfig::loadByName('node', 'comment'),
+      'entity_type' => 'node',
+      'bundle' => 'page',
+      'label' => 'Comment',
+    ])->save();
+
+    // Make two comments
+    $comment1 = $comment_storage->create([
+      'field_name' => 'comment',
+      'comment_body' => 'test',
+      'entity_id' => $node->id(),
+      'entity_type' => 'node',
+      'comment_type' => 'default',
+    ])->save();
+
+    $comment_storage->create([
+      'field_name' => 'comment',
+      'comment_body' => 'test',
+      'entity_id' => $node->id(),
+      'entity_type' => 'node',
+      'comment_type' => 'default',
+      'pid' => $comment1,
+    ])->save();
+
+    // Render the comments.
+    $renderer = \Drupal::service('renderer');
+    $comments = $comment_storage->loadMultiple();
+    foreach ($comments as $comment) {
+      $built = $this->buildEntityView($comment, 'full', NULL);
+      $renderer->renderInIsolation($built);
+    }
+
+    // Make comment 2 an orphan by setting the property to an invalid value.
+    \Drupal::database()->update('comment_field_data')
+      ->fields([$property => 10])
+      ->condition('cid', 2)
+      ->execute();
+    $comment_storage->resetCache();
+    $node_storage->resetCache();
+
+    // Render the comments with an orphan comment.
+    $comments = $comment_storage->loadMultiple();
+    foreach ($comments as $comment) {
+      $built = $this->buildEntityView($comment, 'full', NULL);
+      $renderer->renderInIsolation($built);
+    }
+
+    $node = $node_storage->load($node->id());
+    $built = $this->buildEntityView($node, 'full', NULL);
+    $renderer->renderInIsolation($built);
+  }
+
+  /**
+   * Provides test data for testOrphan.
+   */
+  public static function providerTestOrphan() {
+    return [
+      ['entity_id'],
+      ['uid'],
+      ['pid'],
+    ];
+  }
+
+}

core/modules/comment/tests/src/Kernel/CommentStringIdEntitiesTest.php

@@ -0,0 +1,67 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Kernel;
+
+use Drupal\comment\Entity\CommentType;
+use Drupal\KernelTests\KernelTestBase;
+use Drupal\field\Entity\FieldStorageConfig;
+
+/**
+ * Tests that comment fields cannot be added to entities with non-integer IDs.
+ *
+ * @group comment
+ */
+class CommentStringIdEntitiesTest extends KernelTestBase {
+
+  /**
+   * Modules to install.
+   *
+   * @var array
+   */
+  protected static $modules = [
+    'comment',
+    'user',
+    'field',
+    'field_ui',
+    'entity_test',
+    'text',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->installEntitySchema('comment');
+    $this->installEntitySchema('entity_test_string_id');
+    $this->installSchema('comment', ['comment_entity_statistics']);
+    // Create the comment body field storage.
+    $this->installConfig(['field']);
+  }
+
+  /**
+   * Tests that comment fields cannot be added entities with non-integer IDs.
+   */
+  public function testCommentFieldNonStringId(): void {
+    $this->expectException(\UnexpectedValueException::class);
+    $bundle = CommentType::create([
+      'id' => 'foo',
+      'label' => 'foo',
+      'description' => '',
+      'target_entity_type_id' => 'entity_test_string_id',
+    ]);
+    $bundle->save();
+    $field_storage = FieldStorageConfig::create([
+      'field_name' => 'foo',
+      'entity_type' => 'entity_test_string_id',
+      'settings' => [
+        'comment_type' => 'entity_test_string_id',
+      ],
+      'type' => 'comment',
+    ]);
+    $field_storage->save();
+  }
+
+}

core/modules/comment/tests/src/Kernel/CommentTypeValidationTest.php

@@ -0,0 +1,36 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Kernel;
+
+use Drupal\comment\Entity\CommentType;
+use Drupal\KernelTests\Core\Config\ConfigEntityValidationTestBase;
+
+/**
+ * Tests validation of comment_type entities.
+ *
+ * @group comment
+ */
+class CommentTypeValidationTest extends ConfigEntityValidationTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['comment', 'node'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->entity = CommentType::create([
+      'id' => 'test',
+      'label' => 'Test',
+      'target_entity_type_id' => 'node',
+    ]);
+    $this->entity->save();
+  }
+
+}

core/modules/comment/tests/src/Kernel/CommentUninstallTest.php

@@ -0,0 +1,99 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Kernel;
+
+use Drupal\comment\Tests\CommentTestTrait;
+use Drupal\Core\Extension\ModuleUninstallValidatorException;
+use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\KernelTests\KernelTestBase;
+use Drupal\node\Entity\NodeType;
+
+/**
+ * Tests comment module uninstall.
+ *
+ * @group comment
+ */
+class CommentUninstallTest extends KernelTestBase {
+
+  use CommentTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'comment',
+    'field',
+    'node',
+    'system',
+    'text',
+    'user',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->installEntitySchema('comment');
+    $this->installConfig(['comment']);
+    $this->installSchema('user', ['users_data']);
+
+    NodeType::create([
+      'type' => 'article',
+      'name' => 'Article',
+    ])->save();
+
+    // Create comment field on article so that it adds 'comment_body' field.
+    FieldStorageConfig::create([
+      'type' => 'text_long',
+      'entity_type' => 'comment',
+      'field_name' => 'comment',
+    ])->save();
+    $this->addDefaultCommentField('node', 'article');
+  }
+
+  /**
+   * Tests if comment module uninstall fails if the field exists.
+   */
+  public function testCommentUninstallWithField(): void {
+    // Ensure that the field exists before uninstalling.
+    $field_storage = FieldStorageConfig::loadByName('comment', 'comment_body');
+    $this->assertNotNull($field_storage);
+
+    // Uninstall the comment module which should trigger an exception.
+    $this->expectException(ModuleUninstallValidatorException::class);
+    $this->expectExceptionMessage('The following reasons prevent the modules from being uninstalled: The <em class="placeholder">Comments</em> field type is used in the following field: node.comment');
+    $this->container->get('module_installer')->uninstall(['comment']);
+  }
+
+  /**
+   * Tests if uninstallation succeeds if the field has been deleted beforehand.
+   */
+  public function testCommentUninstallWithoutField(): void {
+    // Tests if uninstall succeeds if the field has been deleted beforehand.
+    // Manually delete the comment_body field before module uninstall.
+    FieldStorageConfig::loadByName('comment', 'comment_body')->delete();
+
+    // Check that the field is now deleted.
+    $field_storage = FieldStorageConfig::loadByName('comment', 'comment_body');
+    $this->assertNull($field_storage);
+
+    // Manually delete the comment field on the node before module uninstall.
+    $field_storage = FieldStorageConfig::loadByName('node', 'comment');
+    $this->assertNotNull($field_storage);
+    $field_storage->delete();
+
+    // Check that the field is now deleted.
+    $field_storage = FieldStorageConfig::loadByName('node', 'comment');
+    $this->assertNull($field_storage);
+
+    field_purge_batch(10);
+    // Ensure that uninstall succeeds even if the field has already been deleted
+    // manually beforehand.
+    $this->container->get('module_installer')->uninstall(['comment']);
+  }
+
+}

core/modules/comment/tests/src/Kernel/CommentValidationTest.php

@@ -0,0 +1,305 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Kernel;
+
+use Drupal\comment\CommentInterface;
+use Drupal\comment\Entity\Comment;
+use Drupal\comment\Entity\CommentType;
+use Drupal\comment\Tests\CommentTestTrait;
+use Drupal\KernelTests\Core\Entity\EntityKernelTestBase;
+use Drupal\node\Entity\Node;
+use Drupal\Tests\field\Traits\EntityReferenceFieldCreationTrait;
+use Drupal\user\Entity\User;
+
+/**
+ * Tests comment validation constraints.
+ *
+ * @group comment
+ */
+class CommentValidationTest extends EntityKernelTestBase {
+  use CommentTestTrait;
+  use EntityReferenceFieldCreationTrait;
+
+  /**
+   * Modules to install.
+   *
+   * @var array
+   */
+  protected static $modules = ['comment', 'node'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->installSchema('comment', ['comment_entity_statistics']);
+    $this->installConfig(['comment']);
+  }
+
+  /**
+   * Tests the comment validation constraints.
+   */
+  public function testValidation(): void {
+    // Add a user.
+    $user = User::create(['name' => 'test', 'status' => TRUE]);
+    $user->save();
+
+    // Add comment type.
+    $this->entityTypeManager->getStorage('comment_type')->create([
+      'id' => 'comment',
+      'label' => 'comment',
+      'target_entity_type_id' => 'node',
+    ])->save();
+
+    // Add comment field to content.
+    $this->entityTypeManager->getStorage('field_storage_config')->create([
+      'entity_type' => 'node',
+      'field_name' => 'comment',
+      'type' => 'comment',
+      'settings' => [
+        'comment_type' => 'comment',
+      ],
+    ])->save();
+
+    // Create a page node type.
+    $this->entityTypeManager->getStorage('node_type')->create([
+      'type' => 'page',
+      'name' => 'page',
+    ])->save();
+
+    // Add comment field to page content.
+    /** @var \Drupal\field\FieldConfigInterface $field */
+    $field = $this->entityTypeManager->getStorage('field_config')->create([
+      'field_name' => 'comment',
+      'entity_type' => 'node',
+      'bundle' => 'page',
+      'label' => 'Comment settings',
+    ]);
+    $field->save();
+
+    $node = $this->entityTypeManager->getStorage('node')->create([
+      'type' => 'page',
+      'title' => 'test',
+    ]);
+    $node->save();
+
+    $comment = $this->entityTypeManager->getStorage('comment')->create([
+      'entity_id' => $node->id(),
+      'entity_type' => 'node',
+      'field_name' => 'comment',
+      'comment_body' => $this->randomMachineName(),
+    ]);
+
+    $violations = $comment->validate();
+    $this->assertCount(0, $violations, 'No violations when validating a default comment.');
+
+    $comment->set('subject', $this->randomString(65));
+    $this->assertLengthViolation($comment, 'subject', 64);
+
+    // Make the subject valid.
+    $comment->set('subject', $this->randomString());
+    $comment->set('name', $this->randomString(61));
+    $this->assertLengthViolation($comment, 'name', 60);
+
+    // Validate a name collision between an anonymous comment author name and an
+    // existing user account name.
+    $comment->set('name', 'test');
+    $comment->set('uid', 0);
+    $violations = $comment->validate();
+    $this->assertCount(1, $violations, "Violation found on author name collision");
+    $this->assertEquals("name", $violations[0]->getPropertyPath());
+    $this->assertEquals('The name you used (test) belongs to a registered user.', $violations[0]->getMessage());
+
+    // Make the name valid.
+    $comment->set('name', 'valid unused name');
+    $comment->set('mail', 'invalid');
+    $violations = $comment->validate();
+    $this->assertCount(1, $violations, 'Violation found when email is invalid');
+    $this->assertEquals('mail.0.value', $violations[0]->getPropertyPath());
+    $this->assertEquals('This value is not a valid email address.', $violations[0]->getMessage());
+
+    $comment->set('mail', NULL);
+    $comment->set('homepage', 'http://example.com/' . $this->randomMachineName(237));
+    $this->assertLengthViolation($comment, 'homepage', 255);
+
+    $comment->set('homepage', 'invalid');
+    $violations = $comment->validate();
+    $this->assertCount(1, $violations, 'Violation found when homepage is invalid');
+    $this->assertEquals('homepage.0.value', $violations[0]->getPropertyPath());
+
+    // @todo This message should be improved in
+    //   https://www.drupal.org/node/2012690.
+    $this->assertEquals('This value should be of the correct primitive type.', $violations[0]->getMessage());
+
+    $comment->set('homepage', NULL);
+    $comment->set('hostname', $this->randomString(129));
+    $this->assertLengthViolation($comment, 'hostname', 128);
+
+    $comment->set('hostname', NULL);
+    $comment->set('thread', $this->randomString(256));
+    $this->assertLengthViolation($comment, 'thread', 255);
+
+    $comment->set('thread', NULL);
+
+    // Force anonymous users to enter contact details.
+    $field->setSetting('anonymous', CommentInterface::ANONYMOUS_MUST_CONTACT);
+    $field->save();
+    // Reset the node entity.
+    \Drupal::entityTypeManager()->getStorage('node')->resetCache([$node->id()]);
+    $node = Node::load($node->id());
+    // Create a new comment with the new field.
+    $comment = $this->entityTypeManager->getStorage('comment')->create([
+      'entity_id' => $node->id(),
+      'entity_type' => 'node',
+      'field_name' => 'comment',
+      'comment_body' => $this->randomMachineName(),
+      'uid' => 0,
+      'name' => '',
+    ]);
+    $violations = $comment->validate();
+    $this->assertCount(1, $violations, 'Violation found when name is required, but empty and UID is anonymous.');
+    $this->assertEquals('name', $violations[0]->getPropertyPath());
+    $this->assertEquals('You have to specify a valid author.', $violations[0]->getMessage());
+
+    // Test creating a default comment with a given user id works.
+    $comment = $this->entityTypeManager->getStorage('comment')->create([
+      'entity_id' => $node->id(),
+      'entity_type' => 'node',
+      'field_name' => 'comment',
+      'comment_body' => $this->randomMachineName(),
+      'uid' => $user->id(),
+    ]);
+    $violations = $comment->validate();
+    $this->assertCount(0, $violations, 'No violations when validating a default comment with an author.');
+
+    // Test specifying a wrong author name does not work.
+    $comment = $this->entityTypeManager->getStorage('comment')->create([
+      'entity_id' => $node->id(),
+      'entity_type' => 'node',
+      'field_name' => 'comment',
+      'comment_body' => $this->randomMachineName(),
+      'uid' => $user->id(),
+      'name' => 'not-test',
+    ]);
+    $violations = $comment->validate();
+    $this->assertCount(1, $violations, 'Violation found when author name and comment author do not match.');
+    $this->assertEquals('name', $violations[0]->getPropertyPath());
+    $this->assertEquals('The specified author name does not match the comment author.', $violations[0]->getMessage());
+  }
+
+  /**
+   * Tests that comments of unpublished nodes are not valid.
+   */
+  public function testValidationOfCommentOfUnpublishedNode(): void {
+    // Create a page node type.
+    $this->entityTypeManager->getStorage('node_type')->create([
+      'type' => 'page',
+      'name' => 'page',
+    ])->save();
+
+    // Create a comment type.
+    CommentType::create([
+      'id' => 'comment',
+      'label' => 'Default comments',
+      'description' => 'Default comment field',
+      'target_entity_type_id' => 'node',
+    ])->save();
+
+    // Add comment and entity reference comment fields.
+    $this->addDefaultCommentField('node', 'page', 'comment');
+    $this->createEntityReferenceField(
+      'node',
+      'page',
+      'entity_reference_comment',
+      'Entity Reference Comment',
+      'comment',
+      'default',
+      ['target_bundles' => ['comment']]
+    );
+
+    $comment_admin_user = $this->drupalCreateUser([
+      'skip comment approval',
+      'post comments',
+      'access comments',
+      'access content',
+      'administer nodes',
+      'administer comments',
+      'bypass node access',
+    ]);
+    $comment_non_admin_user = $this->drupalCreateUser([
+      'access comments',
+      'post comments',
+      'create page content',
+      'edit own comments',
+      'skip comment approval',
+      'access content',
+    ]);
+
+    // Create a node with a comment and make it unpublished.
+    $node1 = $this->entityTypeManager->getStorage('node')->create([
+      'type' => 'page',
+      'title' => 'test 1',
+      'promote' => 1,
+      'status' => 0,
+      'uid' => $comment_non_admin_user->id(),
+    ]);
+    $node1->save();
+    $comment1 = $this->entityTypeManager->getStorage('comment')->create([
+      'entity_id' => $node1->id(),
+      'entity_type' => 'node',
+      'field_name' => 'comment',
+      'comment_body' => $this->randomMachineName(),
+    ]);
+    $comment1->save();
+    $this->assertInstanceOf(Comment::class, $comment1);
+
+    // Create a second published node.
+    /** @var \Drupal\node\Entity\Node $node2 */
+    $node2 = $this->entityTypeManager->getStorage('node')->create([
+      'type' => 'page',
+      'title' => 'test 2',
+      'promote' => 1,
+      'status' => 1,
+      'uid' => $comment_non_admin_user->id(),
+    ]);
+    $node2->save();
+
+    // Test the validation API directly.
+    $this->drupalSetCurrentUser($comment_non_admin_user);
+    $this->assertEquals(\Drupal::currentUser()->id(), $comment_non_admin_user->id());
+    $node2->set('entity_reference_comment', $comment1->id());
+    $violations = $node2->validate();
+    $this->assertCount(1, $violations);
+    $this->assertEquals('entity_reference_comment.0.target_id', $violations[0]->getPropertyPath());
+    $this->assertEquals(sprintf('This entity (%s: %s) cannot be referenced.', $comment1->getEntityTypeId(), $comment1->id()), $violations[0]->getMessage());
+
+    $this->drupalSetCurrentUser($comment_admin_user);
+    $this->assertEquals(\Drupal::currentUser()->id(), $comment_admin_user->id());
+    $node2->set('entity_reference_comment', $comment1->id());
+    $violations = $node2->validate();
+    $this->assertCount(0, $violations);
+  }
+
+  /**
+   * Verifies that a length violation exists for the given field.
+   *
+   * @param \Drupal\comment\CommentInterface $comment
+   *   The comment object to validate.
+   * @param string $field_name
+   *   The field that violates the maximum length.
+   * @param int $length
+   *   Number of characters that was exceeded.
+   *
+   * @internal
+   */
+  protected function assertLengthViolation(CommentInterface $comment, string $field_name, int $length): void {
+    $violations = $comment->validate();
+    $this->assertCount(1, $violations, "Violation found when $field_name is too long.");
+    $this->assertEquals("{$field_name}.0.value", $violations[0]->getPropertyPath());
+    $field_label = $comment->get($field_name)->getFieldDefinition()->getLabel();
+    $this->assertEquals("{$field_label}: may not be longer than {$length} characters.", $violations[0]->getMessage());
+  }
+
+}

core/modules/comment/tests/src/Kernel/Migrate/MigrateCommentStubTest.php

@@ -0,0 +1,63 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Kernel\Migrate;
+
+use Drupal\comment\Entity\CommentType;
+use Drupal\Tests\migrate_drupal\Kernel\MigrateDrupalTestBase;
+use Drupal\migrate_drupal\Tests\StubTestTrait;
+use Drupal\node\Entity\NodeType;
+
+/**
+ * Test stub creation for comment entities.
+ *
+ * @group comment
+ */
+class MigrateCommentStubTest extends MigrateDrupalTestBase {
+
+  use StubTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['comment', 'node'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->installEntitySchema('comment');
+    $this->installEntitySchema('node');
+
+    // Make sure uid 0 is created (default uid for comments is 0).
+    $storage = \Drupal::entityTypeManager()->getStorage('user');
+    // Insert a row for the anonymous user.
+    $storage
+      ->create([
+        'uid' => 0,
+        'status' => 0,
+        'name' => '',
+      ])
+      ->save();
+    // Need at least one node type and comment type present.
+    NodeType::create([
+      'type' => 'testnodetype',
+      'name' => 'Test node type',
+    ])->save();
+    CommentType::create([
+      'id' => 'testcommenttype',
+      'label' => 'Test comment type',
+      'target_entity_type_id' => 'node',
+    ])->save();
+  }
+
+  /**
+   * Tests creation of comment stubs.
+   */
+  public function testStub(): void {
+    $this->performStubTest('comment');
+  }
+
+}

core/modules/comment/tests/src/Kernel/Migrate/d6/MigrateCommentEntityDisplayTest.php

@@ -0,0 +1,75 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Kernel\Migrate\d6;
+
+use Drupal\Core\Entity\Entity\EntityViewDisplay;
+use Drupal\Tests\migrate_drupal\Kernel\d6\MigrateDrupal6TestBase;
+
+/**
+ * Tests the migration of comment entity displays from Drupal 6.
+ *
+ * @group comment
+ * @group migrate_drupal_6
+ */
+class MigrateCommentEntityDisplayTest extends MigrateDrupal6TestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['comment', 'menu_ui'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->installConfig(['comment']);
+    $this->migrateContentTypes();
+    $this->executeMigrations([
+      'd6_node_type',
+      'd6_comment_type',
+      'd6_comment_field',
+      'd6_comment_field_instance',
+      'd6_comment_entity_display',
+    ]);
+  }
+
+  /**
+   * Asserts various aspects of a comment component in an entity view display.
+   *
+   * @param string $id
+   *   The entity ID.
+   * @param string $component_id
+   *   The ID of the display component.
+   *
+   * @internal
+   */
+  protected function assertDisplay(string $id, string $component_id): void {
+    $component = EntityViewDisplay::load($id)->getComponent($component_id);
+    $this->assertIsArray($component);
+    $this->assertSame('hidden', $component['label']);
+    $this->assertSame('comment_default', $component['type']);
+    $this->assertSame(20, $component['weight']);
+  }
+
+  /**
+   * Tests the migrated display configuration.
+   */
+  public function testMigration(): void {
+    $this->assertDisplay('node.article.default', 'comment_node_article');
+    $this->assertDisplay('node.company.default', 'comment_node_company');
+    $this->assertDisplay('node.employee.default', 'comment_node_employee');
+    $this->assertDisplay('node.event.default', 'comment_node_event');
+    $this->assertDisplay('node.forum.default', 'comment_forum');
+    $this->assertDisplay('node.page.default', 'comment_node_page');
+    $this->assertDisplay('node.sponsor.default', 'comment_node_sponsor');
+    $this->assertDisplay('node.story.default', 'comment_node_story');
+    $this->assertDisplay('node.test_event.default', 'comment_node_test_event');
+    $this->assertDisplay('node.test_page.default', 'comment_node_test_page');
+    $this->assertDisplay('node.test_planet.default', 'comment_node_test_planet');
+    $this->assertDisplay('node.test_story.default', 'comment_node_test_story');
+  }
+
+}

core/modules/comment/tests/src/Kernel/Migrate/d6/MigrateCommentEntityFormDisplaySubjectTest.php

@@ -0,0 +1,79 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Kernel\Migrate\d6;
+
+use Drupal\Core\Entity\Entity\EntityFormDisplay;
+use Drupal\Tests\migrate_drupal\Kernel\d6\MigrateDrupal6TestBase;
+
+/**
+ * Tests the migration of comment form's subject display from Drupal 6.
+ *
+ * @group comment
+ * @group migrate_drupal_6
+ */
+class MigrateCommentEntityFormDisplaySubjectTest extends MigrateDrupal6TestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['comment'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->installConfig(['comment']);
+    $this->executeMigrations([
+      'd6_comment_type',
+      'd6_comment_entity_form_display_subject',
+    ]);
+  }
+
+  /**
+   * Asserts that the comment subject field is visible for a node type.
+   *
+   * @param string $id
+   *   The entity form display ID.
+   *
+   * @internal
+   */
+  protected function assertSubjectVisible(string $id): void {
+    $component = EntityFormDisplay::load($id)->getComponent('subject');
+    $this->assertIsArray($component);
+    $this->assertSame('string_textfield', $component['type']);
+    $this->assertSame(10, $component['weight']);
+  }
+
+  /**
+   * Asserts that the comment subject field is not visible for a node type.
+   *
+   * @param string $id
+   *   The entity form display ID.
+   *
+   * @internal
+   */
+  protected function assertSubjectNotVisible(string $id): void {
+    $component = EntityFormDisplay::load($id)->getComponent('subject');
+    $this->assertNull($component);
+  }
+
+  /**
+   * Tests the migrated display configuration.
+   */
+  public function testMigration(): void {
+    $this->assertSubjectVisible('comment.comment_node_article.default');
+    $this->assertSubjectVisible('comment.comment_node_company.default');
+    $this->assertSubjectVisible('comment.comment_node_employee.default');
+    $this->assertSubjectVisible('comment.comment_node_page.default');
+    $this->assertSubjectVisible('comment.comment_node_sponsor.default');
+    $this->assertSubjectNotVisible('comment.comment_node_story.default');
+    $this->assertSubjectVisible('comment.comment_node_test_event.default');
+    $this->assertSubjectVisible('comment.comment_node_test_page.default');
+    $this->assertSubjectVisible('comment.comment_node_test_planet.default');
+    $this->assertSubjectVisible('comment.comment_node_test_story.default');
+  }
+
+}

core/modules/comment/tests/src/Kernel/Migrate/d6/MigrateCommentEntityFormDisplayTest.php

@@ -0,0 +1,73 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Kernel\Migrate\d6;
+
+use Drupal\Core\Entity\Entity\EntityFormDisplay;
+use Drupal\Tests\migrate_drupal\Kernel\d6\MigrateDrupal6TestBase;
+
+/**
+ * Tests the migration of comment form display from Drupal 6.
+ *
+ * @group comment
+ * @group migrate_drupal_6
+ */
+class MigrateCommentEntityFormDisplayTest extends MigrateDrupal6TestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['comment', 'menu_ui'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->installConfig(['comment']);
+    $this->migrateContentTypes();
+    $this->executeMigrations([
+      'd6_comment_type',
+      'd6_comment_field',
+      'd6_comment_field_instance',
+      'd6_comment_entity_form_display',
+    ]);
+  }
+
+  /**
+   * Asserts various aspects of a comment component in an entity form display.
+   *
+   * @param string $id
+   *   The entity ID.
+   * @param string $component_id
+   *   The ID of the form component.
+   *
+   * @internal
+   */
+  protected function assertDisplay(string $id, string $component_id): void {
+    $component = EntityFormDisplay::load($id)->getComponent($component_id);
+    $this->assertIsArray($component);
+    $this->assertSame('comment_default', $component['type']);
+    $this->assertSame(20, $component['weight']);
+  }
+
+  /**
+   * Tests the migrated display configuration.
+   */
+  public function testMigration(): void {
+    $this->assertDisplay('node.article.default', 'comment_node_article');
+    $this->assertDisplay('node.company.default', 'comment_node_company');
+    $this->assertDisplay('node.employee.default', 'comment_node_employee');
+    $this->assertDisplay('node.event.default', 'comment_node_event');
+    $this->assertDisplay('node.forum.default', 'comment_forum');
+    $this->assertDisplay('node.page.default', 'comment_node_page');
+    $this->assertDisplay('node.sponsor.default', 'comment_node_sponsor');
+    $this->assertDisplay('node.story.default', 'comment_node_story');
+    $this->assertDisplay('node.test_event.default', 'comment_node_test_event');
+    $this->assertDisplay('node.test_page.default', 'comment_node_test_page');
+    $this->assertDisplay('node.test_planet.default', 'comment_node_test_planet');
+    $this->assertDisplay('node.test_story.default', 'comment_node_test_story');
+  }
+
+}

core/modules/comment/tests/src/Kernel/Migrate/d6/MigrateCommentFieldInstanceTest.php

@@ -0,0 +1,93 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Kernel\Migrate\d6;
+
+use Drupal\field\Entity\FieldConfig;
+use Drupal\Tests\migrate_drupal\Kernel\d6\MigrateDrupal6TestBase;
+
+/**
+ * Tests the migration of comment field instances from Drupal 6.
+ *
+ * @group comment
+ * @group migrate_drupal_6
+ */
+class MigrateCommentFieldInstanceTest extends MigrateDrupal6TestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['comment', 'menu_ui'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->installConfig(['comment']);
+    $this->migrateContentTypes();
+    $this->executeMigrations([
+      'd6_comment_type',
+      'd6_comment_field',
+      'd6_comment_field_instance',
+    ]);
+  }
+
+  /**
+   * Asserts a comment field instance entity.
+   *
+   * @param string $bundle
+   *   The bundle ID.
+   * @param string $field_name
+   *   The field name.
+   * @param int $default_value
+   *   The field's default_value setting.
+   * @param int $default_mode
+   *   The field's default_mode setting.
+   * @param int $per_page
+   *   The field's per_page setting.
+   * @param int $anonymous
+   *   The field's anonymous setting.
+   * @param bool $form_location
+   *   The field's form_location setting.
+   * @param int $preview
+   *   The field's preview setting.
+   *
+   * @internal
+   */
+  protected function assertEntity(string $bundle, string $field_name, int $default_value, int $default_mode, int $per_page, int $anonymous, bool $form_location, int $preview): void {
+    $entity = FieldConfig::load("node.$bundle.$field_name");
+    $this->assertInstanceOf(FieldConfig::class, $entity);
+    $this->assertSame('node', $entity->getTargetEntityTypeId());
+    $this->assertSame('Comments', $entity->label());
+    $this->assertTrue($entity->isRequired());
+    $this->assertSame($bundle, $entity->getTargetBundle());
+    $this->assertSame($field_name, $entity->getFieldStorageDefinition()->getName());
+    $this->assertSame($default_value, $entity->get('default_value')[0]['status']);
+    $this->assertSame($default_mode, $entity->getSetting('default_mode'));
+    $this->assertSame($per_page, $entity->getSetting('per_page'));
+    $this->assertSame($anonymous, $entity->getSetting('anonymous'));
+    $this->assertSame($form_location, $entity->getSetting('form_location'));
+    $this->assertSame($preview, $entity->getSetting('preview'));
+  }
+
+  /**
+   * Tests the migrated field instance values.
+   */
+  public function testMigration(): void {
+    $this->assertEntity('article', 'comment_node_article', 2, 1, 50, 0, FALSE, 1);
+    $this->assertEntity('company', 'comment_node_company', 2, 1, 50, 0, FALSE, 1);
+    $this->assertEntity('employee', 'comment_node_employee', 2, 1, 50, 0, FALSE, 1);
+    $this->assertEntity('event', 'comment_node_event', 2, 1, 50, 0, FALSE, 1);
+    $this->assertEntity('forum', 'comment_forum', 2, 1, 50, 0, FALSE, 1);
+    $this->assertEntity('page', 'comment_node_page', 0, 1, 50, 0, FALSE, 1);
+    $this->assertEntity('sponsor', 'comment_node_sponsor', 2, 1, 50, 0, FALSE, 1);
+    $this->assertEntity('story', 'comment_node_story', 2, 0, 70, 1, FALSE, 0);
+    $this->assertEntity('test_event', 'comment_node_test_event', 2, 1, 50, 0, FALSE, 1);
+    $this->assertEntity('test_page', 'comment_node_test_page', 2, 1, 50, 0, FALSE, 1);
+    $this->assertEntity('test_planet', 'comment_node_test_planet', 2, 1, 50, 0, FALSE, 1);
+    $this->assertEntity('test_story', 'comment_node_test_story', 2, 1, 50, 0, FALSE, 1);
+  }
+
+}

core/modules/comment/tests/src/Kernel/Migrate/d6/MigrateCommentFieldTest.php

@@ -0,0 +1,69 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Kernel\Migrate\d6;
+
+use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\Tests\migrate_drupal\Kernel\d6\MigrateDrupal6TestBase;
+
+/**
+ * Tests the migration of comment fields from Drupal 6.
+ *
+ * @group comment
+ * @group migrate_drupal_6
+ */
+class MigrateCommentFieldTest extends MigrateDrupal6TestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['comment', 'menu_ui'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->installConfig(['comment']);
+    $this->executeMigrations([
+      'd6_comment_type',
+      'd6_comment_field',
+    ]);
+  }
+
+  /**
+   * Asserts a comment field entity.
+   *
+   * @param string $comment_type
+   *   The comment type.
+   *
+   * @internal
+   */
+  protected function assertEntity(string $comment_type): void {
+    $entity = FieldStorageConfig::load('node.' . $comment_type);
+    $this->assertInstanceOf(FieldStorageConfig::class, $entity);
+    $this->assertSame('node', $entity->getTargetEntityTypeId());
+    $this->assertSame('comment', $entity->getType());
+    $this->assertSame($comment_type, $entity->getSetting('comment_type'));
+  }
+
+  /**
+   * Tests the migrated comment fields.
+   */
+  public function testMigration(): void {
+    $this->assertEntity('comment_node_article');
+    $this->assertEntity('comment_node_company');
+    $this->assertEntity('comment_node_employee');
+    $this->assertEntity('comment_node_event');
+    $this->assertEntity('comment_forum');
+    $this->assertEntity('comment_node_page');
+    $this->assertEntity('comment_node_sponsor');
+    $this->assertEntity('comment_node_story');
+    $this->assertEntity('comment_node_test_event');
+    $this->assertEntity('comment_node_test_page');
+    $this->assertEntity('comment_node_test_planet');
+    $this->assertEntity('comment_node_test_story');
+  }
+
+}

core/modules/comment/tests/src/Kernel/Migrate/d6/MigrateCommentTest.php

@@ -0,0 +1,122 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Kernel\Migrate\d6;
+
+use Drupal\comment\Entity\Comment;
+use Drupal\comment\Tests\CommentTestTrait;
+use Drupal\Tests\migrate_drupal\Kernel\d6\MigrateDrupal6TestBase;
+use Drupal\node\NodeInterface;
+
+/**
+ * Tests the migration of comments from Drupal 6.
+ *
+ * @group comment
+ * @group migrate_drupal_6
+ */
+class MigrateCommentTest extends MigrateDrupal6TestBase {
+
+  use CommentTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'comment',
+    'content_translation',
+    'language',
+    'menu_ui',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->installEntitySchema('node');
+    $this->installEntitySchema('comment');
+    $this->installSchema('comment', ['comment_entity_statistics']);
+    $this->installSchema('node', ['node_access']);
+    $this->installConfig(['comment']);
+
+    $this->migrateContent();
+    $this->executeMigrations([
+      'language',
+      'd6_language_content_settings',
+      'd6_node',
+      'd6_node_translation',
+      'd6_comment_type',
+      'd6_comment_field',
+      'd6_comment_field_instance',
+      'd6_comment_entity_display',
+      'd6_comment_entity_form_display',
+      'd6_comment',
+    ]);
+  }
+
+  /**
+   * Tests the migrated comments.
+   */
+  public function testMigration(): void {
+    $comment = Comment::load(1);
+    $this->assertSame('The first comment.', $comment->getSubject());
+    $this->assertSame('The first comment body.', $comment->comment_body->value);
+    $this->assertSame('filtered_html', $comment->comment_body->format);
+    $this->assertNull($comment->pid->target_id);
+    $this->assertSame('1', $comment->getCommentedEntityId());
+    $this->assertSame('node', $comment->getCommentedEntityTypeId());
+    $this->assertSame('en', $comment->language()->getId());
+    $this->assertSame('comment_node_story', $comment->getTypeId());
+    $this->assertSame('203.0.113.1', $comment->getHostname());
+
+    $node = $comment->getCommentedEntity();
+    $this->assertInstanceOf(NodeInterface::class, $node);
+    $this->assertSame('1', $node->id());
+
+    $comment = Comment::load(2);
+    $this->assertSame('The response to the second comment.', $comment->subject->value);
+    $this->assertSame('3', $comment->pid->target_id);
+    $this->assertSame('203.0.113.2', $comment->getHostname());
+
+    $node = $comment->getCommentedEntity();
+    $this->assertInstanceOf(NodeInterface::class, $node);
+    $this->assertSame('1', $node->id());
+
+    $comment = Comment::load(3);
+    $this->assertSame('The second comment.', $comment->subject->value);
+    $this->assertNull($comment->pid->target_id);
+    $this->assertSame('203.0.113.3', $comment->getHostname());
+
+    $node = $comment->getCommentedEntity();
+    $this->assertInstanceOf(NodeInterface::class, $node);
+    $this->assertSame('1', $node->id());
+
+    // Tests that the language of the comment is migrated from the node.
+    $comment = Comment::load(7);
+    $this->assertSame('Comment to John Smith - EN', $comment->subject->value);
+    $this->assertSame('This is an English comment.', $comment->comment_body->value);
+    $this->assertSame('21', $comment->getCommentedEntityId());
+    $this->assertSame('node', $comment->getCommentedEntityTypeId());
+    $this->assertSame('en', $comment->language()->getId());
+
+    $node = $comment->getCommentedEntity();
+    $this->assertInstanceOf(NodeInterface::class, $node);
+    $this->assertSame('21', $node->id());
+
+    // Tests that the comment language is correct and that the commented entity
+    // is correctly migrated when the comment was posted to a node translation.
+    $comment = Comment::load(8);
+    $this->assertSame('Comment to John Smith - FR', $comment->subject->value);
+    $this->assertSame('This is a French comment.', $comment->comment_body->value);
+    $this->assertSame('21', $comment->getCommentedEntityId());
+    $this->assertSame('node', $comment->getCommentedEntityTypeId());
+    $this->assertSame('fr', $comment->language()->getId());
+
+    $node = $comment->getCommentedEntity();
+    $this->assertInstanceOf(NodeInterface::class, $node);
+    $this->assertSame('21', $node->id());
+  }
+
+}

core/modules/comment/tests/src/Kernel/Migrate/d6/MigrateCommentTypeTest.php

@@ -0,0 +1,147 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Kernel\Migrate\d6;
+
+use Drupal\comment\Entity\CommentType;
+use Drupal\Tests\migrate_drupal\Kernel\d6\MigrateDrupal6TestBase;
+
+/**
+ * Tests the migration of comment types from Drupal 6.
+ *
+ * @group comment
+ * @group migrate_drupal_6
+ */
+class MigrateCommentTypeTest extends MigrateDrupal6TestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['comment'];
+
+  /**
+   * Asserts a comment type entity.
+   *
+   * @param string $id
+   *   The entity ID.
+   * @param string $label
+   *   The entity label.
+   *
+   * @internal
+   */
+  protected function assertEntity(string $id, string $label): void {
+    $entity = CommentType::load($id);
+    $this->assertInstanceOf(CommentType::class, $entity);
+    $this->assertSame($label, $entity->label());
+    $this->assertSame('node', $entity->getTargetEntityTypeId());
+  }
+
+  /**
+   * Tests the migrated comment types.
+   */
+  public function testMigration(): void {
+    $this->installConfig(['comment']);
+    $this->executeMigration('d6_comment_type');
+
+    $this->assertEntity('comment_node_article', 'Article comment');
+    $this->assertEntity('comment_node_company', 'Company comment');
+    $this->assertEntity('comment_node_employee', 'Employee comment');
+    $this->assertEntity('comment_node_event', 'Event comment');
+    $this->assertEntity('comment_forum', 'Forum topic comment');
+    $this->assertEntity('comment_node_page', 'Page comment');
+    $this->assertEntity('comment_node_sponsor', 'Sponsor comment');
+    $this->assertEntity('comment_node_story', 'Story comment');
+    $this->assertEntity('comment_node_test_event', 'Migrate test event comment');
+    $this->assertEntity('comment_node_test_page', 'Migrate test page comment');
+    $this->assertEntity('comment_node_test_planet', 'Migrate test planet comment');
+    $this->assertEntity('comment_node_test_story', 'Migrate test story comment');
+    $this->assertEntity('comment_node_a_thirty_two_char', 'Test long name comment');
+  }
+
+  /**
+   * Tests comment type migration without node or / and comment on source.
+   *
+   * Usually, MigrateDumpAlterInterface::migrateDumpAlter() should be used when
+   * the source fixture needs to be changed in a Migrate kernel test, but that
+   * would end in three additional tests and an extra overhead in maintenance.
+   *
+   * @param string[] $disabled_source_modules
+   *   List of the modules to disable in the source Drupal database.
+   * @param string[][] $expected_messages
+   *   List of the expected migration messages, keyed by the message type.
+   *   Message type should be "status" "warning" or "error".
+   *
+   * @dataProvider providerTestNoCommentTypeMigration
+   */
+  public function testNoCommentTypeMigration(array $disabled_source_modules, array $expected_messages): void {
+    if (!empty($disabled_source_modules)) {
+      $this->sourceDatabase->update('system')
+        ->condition('name', $disabled_source_modules, 'IN')
+        ->fields(['status' => 0])
+        ->execute();
+    }
+
+    $this->startCollectingMessages();
+    $this->executeMigration('d6_comment_type');
+
+    $expected_messages += [
+      'status' => [],
+      'warning' => [],
+      'error' => [],
+    ];
+    $actual_messages = $this->migrateMessages + [
+      'status' => [],
+      'warning' => [],
+      'error' => [],
+    ];
+
+    foreach ($expected_messages as $type => $expected_messages_by_type) {
+      $this->assertSameSize($expected_messages_by_type, $actual_messages[$type]);
+      // Cast the actual messages to string.
+      $actual_messages_by_type = array_reduce($actual_messages[$type], function (array $carry, $actual_message) {
+        $carry[] = (string) $actual_message;
+        return $carry;
+      }, []);
+      $missing_expected_messages_by_type = array_diff($expected_messages_by_type, $actual_messages_by_type);
+      $unexpected_messages_by_type = array_diff($actual_messages_by_type, $expected_messages_by_type);
+      $this->assertEmpty($unexpected_messages_by_type, sprintf('No additional messages are present with type "%s". This expectation is wrong, because there are additional messages present: "%s"', $type, implode('", "', $unexpected_messages_by_type)));
+      $this->assertEmpty($missing_expected_messages_by_type, sprintf('Every expected messages are present with type "%s". This expectation is wrong, because the following messages aren\'t present: "%s"', $type, implode('", "', $missing_expected_messages_by_type)));
+    }
+
+    $this->assertEmpty(CommentType::loadMultiple());
+  }
+
+  /**
+   * Provides test cases for ::testNoCommentTypeMigration().
+   */
+  public static function providerTestNoCommentTypeMigration() {
+    return [
+      'Node module is disabled in source' => [
+        'disabled_source_modules' => ['node'],
+        'expected_messages' => [
+          'error' => [
+            'Migration d6_comment_type did not meet the requirements. The node module is not enabled in the source site.',
+          ],
+        ],
+      ],
+      'Comment module is disabled in source' => [
+        'disabled_source_modules' => ['comment'],
+        'expected_messages' => [
+          'error' => [
+            'Migration d6_comment_type did not meet the requirements. The module comment is not enabled in the source site.',
+          ],
+        ],
+      ],
+      'Node and comment modules are disabled in source' => [
+        'disabled_source_modules' => ['comment', 'node'],
+        'expected_messages' => [
+          'error' => [
+            'Migration d6_comment_type did not meet the requirements. The module comment is not enabled in the source site.',
+          ],
+        ],
+      ],
+    ];
+  }
+
+}

core/modules/comment/tests/src/Kernel/Migrate/d7/CommentEntityTranslationCheckRequirementsTest.php

@@ -0,0 +1,58 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Kernel\Migrate\d7;
+
+use Drupal\Tests\migrate_drupal\Kernel\d7\MigrateDrupal7TestBase;
+use Drupal\migrate\Exception\RequirementsException;
+
+/**
+ * Tests check requirements for comment entity translation source plugin.
+ *
+ * @group comment
+ */
+class CommentEntityTranslationCheckRequirementsTest extends MigrateDrupal7TestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'content_translation',
+    'comment',
+    'language',
+  ];
+
+  /**
+   * Tests exception thrown when the given module is not enabled in the source.
+   *
+   * @dataProvider providerTestCheckRequirements
+   */
+  public function testCheckRequirements($module): void {
+    // Disable the module in the source site.
+    $this->sourceDatabase->update('system')
+      ->condition('name', $module)
+      ->fields([
+        'status' => '0',
+      ])
+      ->execute();
+    $this->expectException(RequirementsException::class);
+    $this->expectExceptionMessage("The module $module is not enabled in the source site");
+    $this->getMigration('d7_comment_entity_translation')
+      ->getSourcePlugin()
+      ->checkRequirements();
+  }
+
+  /**
+   * Provides data for testCheckRequirements.
+   *
+   * @return string[][]
+   */
+  public static function providerTestCheckRequirements() {
+    return [
+      ['comment'],
+      ['node'],
+    ];
+  }
+
+}

core/modules/comment/tests/src/Kernel/Migrate/d7/MigrateCommentEntityDisplayTest.php

@@ -0,0 +1,67 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Kernel\Migrate\d7;
+
+use Drupal\Core\Entity\Entity\EntityViewDisplay;
+use Drupal\Tests\migrate_drupal\Kernel\d7\MigrateDrupal7TestBase;
+
+/**
+ * Tests the migration of comment entity displays from Drupal 7.
+ *
+ * @group comment
+ * @group migrate_drupal_7
+ */
+class MigrateCommentEntityDisplayTest extends MigrateDrupal7TestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['node', 'comment', 'text', 'menu_ui'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->migrateContentTypes();
+    $this->migrateCommentTypes();
+    $this->executeMigrations([
+      'd7_comment_field',
+      'd7_comment_field_instance',
+      'd7_comment_entity_display',
+    ]);
+  }
+
+  /**
+   * Asserts various aspects of a comment component in an entity view display.
+   *
+   * @param string $id
+   *   The entity ID.
+   * @param string $component_id
+   *   The ID of the display component.
+   *
+   * @internal
+   */
+  protected function assertDisplay(string $id, string $component_id): void {
+    $component = EntityViewDisplay::load($id)->getComponent($component_id);
+    $this->assertIsArray($component);
+    $this->assertSame('hidden', $component['label']);
+    $this->assertSame('comment_default', $component['type']);
+    $this->assertSame(20, $component['weight']);
+  }
+
+  /**
+   * Tests the migrated display configuration.
+   */
+  public function testMigration(): void {
+    $this->assertDisplay('node.page.default', 'comment_node_page');
+    $this->assertDisplay('node.article.default', 'comment_node_article');
+    $this->assertDisplay('node.book.default', 'comment_node_book');
+    $this->assertDisplay('node.blog.default', 'comment_node_blog');
+    $this->assertDisplay('node.forum.default', 'comment_forum');
+    $this->assertDisplay('node.test_content_type.default', 'comment_node_test_content_type');
+  }
+
+}

core/modules/comment/tests/src/Kernel/Migrate/d7/MigrateCommentEntityFormDisplaySubjectTest.php

@@ -0,0 +1,72 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Kernel\Migrate\d7;
+
+use Drupal\Core\Entity\Entity\EntityFormDisplay;
+use Drupal\Tests\migrate_drupal\Kernel\d7\MigrateDrupal7TestBase;
+
+/**
+ * Tests the migration of comment form's subject display from Drupal 7.
+ *
+ * @group comment
+ * @group migrate_drupal_7
+ */
+class MigrateCommentEntityFormDisplaySubjectTest extends MigrateDrupal7TestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['node', 'comment', 'text', 'menu_ui'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->migrateCommentTypes();
+    $this->executeMigration('d7_comment_entity_form_display_subject');
+  }
+
+  /**
+   * Asserts that the comment subject field is visible for a node type.
+   *
+   * @param string $id
+   *   The entity form display ID.
+   *
+   * @internal
+   */
+  protected function assertSubjectVisible(string $id): void {
+    $component = EntityFormDisplay::load($id)->getComponent('subject');
+    $this->assertIsArray($component);
+    $this->assertSame('string_textfield', $component['type']);
+    $this->assertSame(10, $component['weight']);
+  }
+
+  /**
+   * Asserts that the comment subject field is not visible for a node type.
+   *
+   * @param string $id
+   *   The entity form display ID.
+   *
+   * @internal
+   */
+  protected function assertSubjectNotVisible(string $id): void {
+    $component = EntityFormDisplay::load($id)->getComponent('subject');
+    $this->assertNull($component);
+  }
+
+  /**
+   * Tests the migrated display configuration.
+   */
+  public function testMigration(): void {
+    $this->assertSubjectVisible('comment.comment_node_page.default');
+    $this->assertSubjectVisible('comment.comment_node_article.default');
+    $this->assertSubjectVisible('comment.comment_node_book.default');
+    $this->assertSubjectVisible('comment.comment_node_blog.default');
+    $this->assertSubjectVisible('comment.comment_forum.default');
+    $this->assertSubjectNotVisible('comment.comment_node_test_content_type.default');
+  }
+
+}

core/modules/comment/tests/src/Kernel/Migrate/d7/MigrateCommentEntityFormDisplayTest.php

@@ -0,0 +1,66 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\comment\Kernel\Migrate\d7;
+
+use Drupal\Core\Entity\Entity\EntityFormDisplay;
+use Drupal\Tests\migrate_drupal\Kernel\d7\MigrateDrupal7TestBase;
+
+/**
+ * Tests the migration of comment form display from Drupal 7.
+ *
+ * @group comment
+ * @group migrate_drupal_7
+ */
+class MigrateCommentEntityFormDisplayTest extends MigrateDrupal7TestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['node', 'comment', 'text', 'menu_ui'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->migrateContentTypes();
+    $this->migrateCommentTypes();
+    $this->executeMigrations([
+      'd7_comment_field',
+      'd7_comment_field_instance',
+      'd7_comment_entity_form_display',
+    ]);
+  }
+
+  /**
+   * Asserts various aspects of a comment component in an entity form display.
+   *
+   * @param string $id
+   *   The entity ID.
+   * @param string $component_id
+   *   The ID of the form component.
+   *
+   * @internal
+   */
+  protected function assertDisplay(string $id, string $component_id): void {
+    $component = EntityFormDisplay::load($id)->getComponent($component_id);
+    $this->assertIsArray($component);
+    $this->assertSame('comment_default', $component['type']);
+    $this->assertSame(20, $component['weight']);
+  }
+
+  /**
+   * Tests the migrated display configuration.
+   */
+  public function testMigration(): void {
+    $this->assertDisplay('node.page.default', 'comment_node_page');
+    $this->assertDisplay('node.article.default', 'comment_node_article');
+    $this->assertDisplay('node.book.default', 'comment_node_book');
+    $this->assertDisplay('node.blog.default', 'comment_node_blog');
+    $this->assertDisplay('node.forum.default', 'comment_forum');
+    $this->assertDisplay('node.test_content_type.default', 'comment_node_test_content_type');
+  }
+
+}