first commit

core/modules/forum/tests/modules/forum_test_views/forum_test_views.info.yml

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

core/modules/forum/tests/modules/forum_test_views/test_views/views.view.test_forum_index.yml

@@ -0,0 +1,148 @@
+langcode: en
+status: true
+dependencies: {  }
+id: test_forum_index
+label: test_forum_index
+module: views
+description: ''
+tag: ''
+base_table: forum_index
+base_field: nid
+display:
+  default:
+    display_plugin: default
+    id: default
+    display_title: Default
+    position: null
+    display_options:
+      access:
+        type: none
+      cache:
+        type: tag
+      query:
+        type: views_query
+      exposed_form:
+        type: basic
+      pager:
+        type: full
+      style:
+        type: default
+      row:
+        type: fields
+      fields:
+        nid:
+          table: forum_index
+          field: nid
+          id: nid
+        sticky:
+          id: sticky
+          table: forum_index
+          field: sticky
+          relationship: none
+          group_type: group
+          admin_label: ''
+          label: Sticky
+          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
+          type: yes-no
+          type_custom_true: ''
+          type_custom_false: ''
+          not: false
+          plugin_id: boolean
+        comment_count:
+          id: comment_count
+          table: forum_index
+          field: comment_count
+          relationship: none
+          group_type: group
+          admin_label: ''
+          label: 'Comment count'
+          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: .
+          separator: ','
+          format_plural: false
+          format_plural_string: "1\x03@count"
+          prefix: ''
+          suffix: ''
+          plugin_id: numeric
+      filters: {  }
+      sorts: {  }

core/modules/forum/tests/modules/forum_url_alter_test/forum_url_alter_test.info.yml

@@ -0,0 +1,10 @@
+name: 'forum_Url_alter tests'
+type: module
+description: 'A support module to test altering the inbound and outbound path.'
+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/forum/tests/modules/forum_url_alter_test/forum_url_alter_test.services.yml

@@ -0,0 +1,6 @@
+services:
+  forum_url_alter_test.path_processor:
+    class: Drupal\forum_url_alter_test\PathProcessorTest
+    tags:
+      - { name: path_processor_inbound, priority: 800 }
+      - { name: path_processor_outbound, priority: 100 }

core/modules/forum/tests/modules/forum_url_alter_test/src/PathProcessorTest.php

@@ -0,0 +1,31 @@
+<?php
+
+namespace Drupal\forum_url_alter_test;
+
+use Drupal\Core\PathProcessor\InboundPathProcessorInterface;
+use Drupal\Core\PathProcessor\OutboundPathProcessorInterface;
+use Drupal\Core\Render\BubbleableMetadata;
+use Symfony\Component\HttpFoundation\Request;
+
+/**
+ * Path processor for url_alter_test.
+ */
+class PathProcessorTest implements InboundPathProcessorInterface, OutboundPathProcessorInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function processInbound($path, Request $request) {
+    // Rewrite community/ to forum/.
+    return preg_replace('@^/community(.*)@', '/forum$1', $path);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function processOutbound($path, &$options = [], ?Request $request = NULL, ?BubbleableMetadata $bubbleable_metadata = NULL) {
+    // Rewrite forum/ to community/.
+    return preg_replace('@^/forum(.*)@', '/community$1', $path);
+  }
+
+}

core/modules/forum/tests/src/Functional/ForumBlockTest.php

@@ -0,0 +1,192 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Functional;
+
+use Drupal\Component\Render\FormattableMarkup;
+use Drupal\Core\Datetime\DrupalDateTime;
+use Drupal\comment\Entity\Comment;
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests the forum blocks.
+ *
+ * @group forum
+ * @group legacy
+ */
+class ForumBlockTest extends BrowserTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  protected static $modules = ['forum', 'block'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * A user with various administrative privileges.
+   */
+  protected $adminUser;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // Create users.
+    $this->adminUser = $this->drupalCreateUser([
+      'access administration pages',
+      'administer blocks',
+      'administer nodes',
+      'create forum content',
+      'post comments',
+      'skip comment approval',
+    ]);
+  }
+
+  /**
+   * Tests the "New forum topics" block.
+   */
+  public function testNewForumTopicsBlock(): void {
+    $this->drupalLogin($this->adminUser);
+
+    // Enable the new forum topics block.
+    $block = $this->drupalPlaceBlock('forum_new_block');
+    $this->drupalGet('');
+
+    // Create 5 forum topics.
+    $topics = $this->createForumTopics();
+
+    $this->assertSession()->linkExists('More', 0, 'New forum topics block has a "more"-link.');
+    $this->assertSession()->linkByHrefExists('forum', 0, 'New forum topics block has a "more"-link.');
+
+    // We expect all 5 forum topics to appear in the "New forum topics" block.
+    foreach ($topics as $topic) {
+      $this->assertSession()->linkExists($topic, 0, new FormattableMarkup('Forum topic @topic found in the "New forum topics" block.', ['@topic' => $topic]));
+    }
+
+    // Configure the new forum topics block to only show 2 topics.
+    $block->getPlugin()->setConfigurationValue('block_count', 2);
+    $block->save();
+
+    $this->drupalGet('');
+    // We expect only the 2 most recent forum topics to appear in the "New forum
+    // topics" block.
+    for ($index = 0; $index < 5; $index++) {
+      if (in_array($index, [3, 4])) {
+        $this->assertSession()->linkExists($topics[$index], 0, new FormattableMarkup('Forum topic @topic found in the "New forum topics" block.', ['@topic' => $topics[$index]]));
+      }
+      else {
+        $this->assertSession()->pageTextNotContains($topics[$index]);
+      }
+    }
+  }
+
+  /**
+   * Tests the "Active forum topics" block.
+   */
+  public function testActiveForumTopicsBlock(): void {
+    $this->drupalLogin($this->adminUser);
+
+    // Create 10 forum topics.
+    $topics = $this->createForumTopics(10);
+
+    // Comment on the first 5 topics.
+    $date = new DrupalDateTime();
+    for ($index = 0; $index < 5; $index++) {
+      // Get the node from the topic title.
+      $node = $this->drupalGetNodeByTitle($topics[$index]);
+      $date->modify('+1 minute');
+      $comment = Comment::create([
+        'entity_id' => $node->id(),
+        'field_name' => 'comment_forum',
+        'entity_type' => 'node',
+        'node_type' => 'node_type_' . $node->bundle(),
+        'subject' => $this->randomString(20),
+        'comment_body' => $this->randomString(256),
+        'created' => $date->getTimestamp(),
+      ]);
+      $comment->save();
+    }
+
+    // Enable the block.
+    $block = $this->drupalPlaceBlock('forum_active_block');
+    $this->drupalGet('');
+    $this->assertSession()->linkExists('More', 0, 'Active forum topics block has a "more"-link.');
+    $this->assertSession()->linkByHrefExists('forum', 0, 'Active forum topics block has a "more"-link.');
+
+    // We expect the first 5 forum topics to appear in the "Active forum topics"
+    // block.
+    $this->drupalGet('<front>');
+    for ($index = 0; $index < 10; $index++) {
+      if ($index < 5) {
+        $this->assertSession()->linkExists($topics[$index], 0, new FormattableMarkup('Forum topic @topic found in the "Active forum topics" block.', ['@topic' => $topics[$index]]));
+      }
+      else {
+        $this->assertSession()->pageTextNotContains($topics[$index]);
+      }
+    }
+
+    // Configure the active forum block to only show 2 topics.
+    $block->getPlugin()->setConfigurationValue('block_count', 2);
+    $block->save();
+
+    $this->drupalGet('');
+
+    // We expect only the 2 forum topics with most recent comments to appear in
+    // the "Active forum topics" block.
+    for ($index = 0; $index < 10; $index++) {
+      if (in_array($index, [3, 4])) {
+        $this->assertSession()->linkExists($topics[$index], 0, 'Forum topic found in the "Active forum topics" block.');
+      }
+      else {
+        $this->assertSession()->pageTextNotContains($topics[$index]);
+      }
+    }
+  }
+
+  /**
+   * Creates a forum topic.
+   *
+   * @return string
+   *   The title of the newly generated topic.
+   */
+  protected function createForumTopics($count = 5) {
+    $topics = [];
+    $date = new DrupalDateTime();
+    $date->modify('-24 hours');
+
+    for ($index = 0; $index < $count; $index++) {
+      // Generate a random subject/body.
+      $title = $this->randomMachineName(20);
+      $body = $this->randomMachineName(200);
+      // Forum posts are ordered by timestamp, so force a unique timestamp by
+      // changing the date.
+      $date->modify('+1 minute');
+
+      $edit = [
+        'title[0][value]' => $title,
+        'body[0][value]' => $body,
+        // Forum posts are ordered by timestamp, so force a unique timestamp by
+        // adding the index.
+        'created[0][value][date]' => $date->format('Y-m-d'),
+        'created[0][value][time]' => $date->format('H:i:s'),
+      ];
+
+      // Create the forum topic, preselecting the forum ID via a URL parameter.
+      $this->drupalGet('node/add/forum', ['query' => ['forum_id' => 1]]);
+      $this->submitForm($edit, 'Save');
+      $topics[] = $title;
+    }
+
+    return $topics;
+  }
+
+}

core/modules/forum/tests/src/Functional/ForumIndexTest.php

@@ -0,0 +1,104 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests the forum index listing.
+ *
+ * @group forum
+ * @group legacy
+ */
+class ForumIndexTest extends BrowserTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  protected static $modules = ['taxonomy', 'comment', 'forum'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // Create a test user.
+    $web_user = $this->drupalCreateUser([
+      'create forum content',
+      'edit own forum content',
+      'edit any forum content',
+      'administer nodes',
+      'administer forums',
+    ]);
+    $this->drupalLogin($web_user);
+  }
+
+  /**
+   * Tests the forum index for published and unpublished nodes.
+   */
+  public function testForumIndexStatus(): void {
+    // The forum ID to use.
+    $tid = 1;
+
+    // Create a test node.
+    $title = $this->randomMachineName(20);
+    $edit = [
+      'title[0][value]' => $title,
+      'body[0][value]' => $this->randomMachineName(200),
+    ];
+
+    // Create the forum topic, preselecting the forum ID via a URL parameter.
+    $this->drupalGet("forum/$tid");
+    $this->clickLink('Add new Forum topic');
+    $this->assertSession()->addressEquals("node/add/forum?forum_id=$tid");
+    $this->submitForm($edit, 'Save');
+
+    // Check that the node exists in the database.
+    $node = $this->drupalGetNodeByTitle($title);
+    $this->assertNotEmpty($node, 'New forum node found in database.');
+
+    // Create a child forum.
+    $edit = [
+      'name[0][value]' => $this->randomMachineName(20),
+      'description[0][value]' => $this->randomMachineName(200),
+      'parent[0]' => $tid,
+    ];
+    $this->drupalGet('admin/structure/forum/add/forum');
+    $this->submitForm($edit, 'Save');
+    $this->assertSession()->linkExists('edit forum');
+
+    $tid_child = $tid + 1;
+
+    // Verify that the node appears on the index.
+    $this->drupalGet('forum/' . $tid);
+    $this->assertSession()->pageTextContains($title);
+    $this->assertSession()->responseHeaderContains('X-Drupal-Cache-Tags', 'node_list');
+    $this->assertSession()->responseHeaderContains('X-Drupal-Cache-Tags', 'config:node.type.forum');
+    $this->assertSession()->responseHeaderContains('X-Drupal-Cache-Tags', 'comment_list');
+    $this->assertSession()->responseHeaderContains('X-Drupal-Cache-Tags', 'node:' . $node->id());
+    $this->assertSession()->responseHeaderContains('X-Drupal-Cache-Tags', 'taxonomy_term:' . $tid);
+    $this->assertSession()->responseHeaderContains('X-Drupal-Cache-Tags', 'taxonomy_term:' . $tid_child);
+
+    // Unpublish the node.
+    $edit = ['status[value]' => FALSE];
+    $this->drupalGet('node/' . $node->id() . '/edit');
+    $this->submitForm($edit, 'Save');
+    $this->drupalGet('node/' . $node->id());
+    $this->assertSession()->pageTextContains('Access denied');
+
+    // Verify that the node no longer appears on the index.
+    $this->drupalGet('forum/' . $tid);
+    $this->assertSession()->pageTextNotContains($title);
+  }
+
+}

core/modules/forum/tests/src/Functional/ForumIndexUpdateTest.php

@@ -0,0 +1,71 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Functional;
+
+use Drupal\Core\Site\Settings;
+use Drupal\FunctionalTests\Update\UpdatePathTestBase;
+
+/**
+ * Tests addition of the forum_index primary key.
+ *
+ * @group forum
+ */
+final class ForumIndexUpdateTest extends UpdatePathTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setDatabaseDumpFiles() {
+    $this->databaseDumpFiles = [
+      dirname(__DIR__, 2) . '/fixtures/update/drupal-10.1.0.empty.testing.forum.gz',
+    ];
+  }
+
+  /**
+   * Tests the update path to add the new primary key.
+   */
+  public function testUpdatePath(): void {
+    // Set the batch size to 1 to validate the sandbox logic in the update hook.
+    $settings = Settings::getInstance() ? Settings::getAll() : [];
+    $settings['entity_update_batch_size'] = 1;
+    new Settings($settings);
+
+    $schema = \Drupal::database()->schema();
+    // We can't reliably call ::indexExists for each database driver as sqlite
+    // doesn't have named indexes for primary keys like mysql (PRIMARY) and
+    // pgsql (pkey).
+    $find_primary_key_columns = new \ReflectionMethod(get_class($schema), 'findPrimaryKeyColumns');
+    $columns = $find_primary_key_columns->invoke($schema, 'forum_index');
+    $this->assertEmpty($columns);
+    $count = \Drupal::database()->select('forum_index')->countQuery()->execute()->fetchField();
+    $this->assertEquals(9, $count);
+    $duplicates = \Drupal::database()->select('forum_index')->condition('nid', 1)->countQuery()->execute()->fetchField();
+    $this->assertEquals(2, $duplicates);
+    $duplicates = \Drupal::database()->select('forum_index')->condition('nid', 2)->countQuery()->execute()->fetchField();
+    $this->assertEquals(3, $duplicates);
+    $this->runUpdates();
+    $this->assertEquals(['nid', 'tid'], $find_primary_key_columns->invoke($schema, 'forum_index'));
+    $count = \Drupal::database()->select('forum_index')->countQuery()->execute()->fetchField();
+    $this->assertEquals(6, $count);
+    $duplicates = \Drupal::database()->select('forum_index')->condition('nid', 1)->countQuery()->execute()->fetchField();
+    $this->assertEquals(1, $duplicates);
+    $duplicates = \Drupal::database()->select('forum_index')->condition('nid', 2)->countQuery()->execute()->fetchField();
+    $this->assertEquals(1, $duplicates);
+    // This entry is associated with two terms so two records should remain.
+    $duplicates = \Drupal::database()->select('forum_index')->condition('nid', 4)->countQuery()->execute()->fetchField();
+    $this->assertEquals(2, $duplicates);
+    $entry = \Drupal::database()->select('forum_index', 'f')->fields('f')->condition('nid', 5)->execute()->fetchAssoc();
+    $this->assertEquals([
+      'nid' => 5,
+      'title' => 'AFL',
+      'tid' => 5,
+      'sticky' => 0,
+      'created' => 1695264369,
+      'last_comment_timestamp' => 1695264403,
+      'comment_count' => 1,
+    ], $entry);
+  }
+
+}

core/modules/forum/tests/src/Functional/ForumNodeAccessTest.php

@@ -0,0 +1,110 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+use Drupal\node\Entity\NodeType;
+
+/**
+ * Tests forum block view for private node access.
+ *
+ * @group forum
+ * @group legacy
+ */
+class ForumNodeAccessTest extends BrowserTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  protected static $modules = [
+    'node',
+    'comment',
+    'forum',
+    'taxonomy',
+    'node_access_test',
+    'block',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    node_access_rebuild();
+    node_access_test_add_field(NodeType::load('forum'));
+    \Drupal::state()->set('node_access_test.private', TRUE);
+  }
+
+  /**
+   * Creates some users and creates a public node and a private node.
+   *
+   * Adds both active forum topics and new forum topics blocks to the sidebar.
+   * Tests to ensure private node/public node access is respected on blocks.
+   */
+  public function testForumNodeAccess(): void {
+    // Create some users.
+    $access_user = $this->drupalCreateUser(['node test view']);
+    $no_access_user = $this->drupalCreateUser();
+    $admin_user = $this->drupalCreateUser([
+      'access administration pages',
+      'administer modules',
+      'administer blocks',
+      'create forum content',
+    ]);
+
+    $this->drupalLogin($admin_user);
+
+    // Create a private node.
+    $private_node_title = $this->randomMachineName(20);
+    $edit = [
+      'title[0][value]' => $private_node_title,
+      'body[0][value]' => $this->randomMachineName(200),
+      'private[0][value]' => TRUE,
+    ];
+    $this->drupalGet('node/add/forum', ['query' => ['forum_id' => 1]]);
+    $this->submitForm($edit, 'Save');
+    $private_node = $this->drupalGetNodeByTitle($private_node_title);
+    $this->assertNotEmpty($private_node, 'New private forum node found in database.');
+
+    // Create a public node.
+    $public_node_title = $this->randomMachineName(20);
+    $edit = [
+      'title[0][value]' => $public_node_title,
+      'body[0][value]' => $this->randomMachineName(200),
+    ];
+    $this->drupalGet('node/add/forum', ['query' => ['forum_id' => 1]]);
+    $this->submitForm($edit, 'Save');
+    $public_node = $this->drupalGetNodeByTitle($public_node_title);
+    $this->assertNotEmpty($public_node, 'New public forum node found in database.');
+
+    // Enable the new and active forum blocks.
+    $this->drupalPlaceBlock('forum_active_block');
+    $this->drupalPlaceBlock('forum_new_block');
+
+    // Test for $access_user.
+    $this->drupalLogin($access_user);
+    $this->drupalGet('');
+
+    // Ensure private node and public node are found.
+    $this->assertSession()->pageTextContains($private_node->getTitle());
+    $this->assertSession()->pageTextContains($public_node->getTitle());
+
+    // Test for $no_access_user.
+    $this->drupalLogin($no_access_user);
+    $this->drupalGet('');
+
+    // Ensure private node is not found but public is found.
+    $this->assertSession()->pageTextNotContains($private_node->getTitle());
+    $this->assertSession()->pageTextContains($public_node->getTitle());
+  }
+
+}

core/modules/forum/tests/src/Functional/ForumTermAccessTest.php

@@ -0,0 +1,96 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+use Drupal\taxonomy\Entity\Term;
+
+/**
+ * Tests forum taxonomy terms for access.
+ *
+ * @group forum
+ * @group legacy
+ */
+class ForumTermAccessTest extends BrowserTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  protected static $modules = [
+    'forum',
+    'taxonomy',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Creates some users and creates a public forum and an unpublished forum.
+   *
+   * Adds both published and unpublished forums.
+   * Tests to ensure publish/unpublished forums access is respected.
+   */
+  public function testForumTermAccess(): void {
+    $assert_session = $this->assertSession();
+    // Create some users.
+    $public_user = $this->drupalCreateUser(['access content']);
+    $admin_user = $this->drupalCreateUser([
+      'access administration pages',
+      'administer forums',
+      'administer taxonomy',
+      'access taxonomy overview',
+    ]);
+
+    $this->drupalLogin($admin_user);
+    // The vocabulary for forums.
+    $vid = $this->config('forum.settings')->get('vocabulary');
+    // Create an unpublished forum.
+    $unpublished_forum_name = $this->randomMachineName(8);
+    $unpublished_forum = Term::create([
+      'vid' => $vid,
+      'name' => $unpublished_forum_name,
+      'status' => 0,
+    ]);
+    $unpublished_forum->save();
+
+    // Create a new published forum.
+    $published_forum_name = $this->randomMachineName(8);
+    $published_forum = Term::create([
+      'vid' => $vid,
+      'name' => $published_forum_name,
+      'status' => 1,
+    ]);
+    $published_forum->save();
+
+    // Test for admin user.
+    // Go to the Forum index page.
+    $this->drupalGet('forum');
+    // The unpublished forum should be in this page for an admin user.
+    $assert_session->pageTextContains($unpublished_forum_name);
+    // Go to the unpublished forum page.
+    $this->drupalGet('forum/' . $unpublished_forum->id());
+    $assert_session->statusCodeEquals(200);
+    $assert_session->pageTextContains($unpublished_forum_name);
+
+    // Test for public user.
+    $this->drupalLogin($public_user);
+    // Go to the Forum index page.
+    $this->drupalGet('forum');
+    // The published forum should be in this page.
+    $assert_session->pageTextContains($published_forum_name);
+    // The unpublished forum should not be in this page.
+    $assert_session->pageTextNotContains($unpublished_forum_name);
+    // Go to the unpublished forum page.
+    $this->drupalGet('forum/' . $unpublished_forum->id());
+    // Public should not be able to access the unpublished forum.
+    $assert_session->statusCodeEquals(403);
+    $assert_session->pageTextNotContains($unpublished_forum_name);
+  }
+
+}

core/modules/forum/tests/src/Functional/ForumTest.php

@@ -0,0 +1,753 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Functional;
+
+use Drupal\Core\Entity\Entity\EntityFormDisplay;
+use Drupal\Core\Entity\Entity\EntityViewDisplay;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Link;
+use Drupal\Core\Url;
+use Drupal\taxonomy\Entity\Vocabulary;
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests for forum.module.
+ *
+ * Create, view, edit, delete, and change forum entries and verify its
+ * consistency in the database.
+ *
+ * @group forum
+ * @group legacy
+ * @group #slow
+ */
+class ForumTest extends BrowserTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  protected static $modules = [
+    'taxonomy',
+    'comment',
+    'forum',
+    'node',
+    'block',
+    'menu_ui',
+    'help',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'starterkit_theme';
+
+  /**
+   * A user with various administrative privileges.
+   */
+  protected $adminUser;
+
+  /**
+   * A user that can create forum topics and edit its own topics.
+   */
+  protected $editOwnTopicsUser;
+
+  /**
+   * A user that can create, edit, and delete forum topics.
+   */
+  protected $editAnyTopicsUser;
+
+  /**
+   * A user with no special privileges.
+   */
+  protected $webUser;
+
+  /**
+   * An administrative user who can bypass comment approval.
+   */
+  protected $postCommentUser;
+
+  /**
+   * An array representing a forum container.
+   */
+  protected $forumContainer;
+
+  /**
+   * An array representing a forum.
+   */
+  protected $forum;
+
+  /**
+   * An array representing a root forum.
+   */
+  protected $rootForum;
+
+  /**
+   * An array of forum topic node IDs.
+   */
+  protected $nids;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->drupalPlaceBlock('system_breadcrumb_block');
+    $this->drupalPlaceBlock('page_title_block');
+
+    // Create users.
+    $this->adminUser = $this->drupalCreateUser([
+      'access administration pages',
+      'access help pages',
+      'administer modules',
+      'administer blocks',
+      'administer forums',
+      'administer menu',
+      'administer taxonomy',
+      'create forum content',
+      'access comments',
+    ]);
+    $this->editAnyTopicsUser = $this->drupalCreateUser([
+      'access administration pages',
+      'access help pages',
+      'create forum content',
+      'edit any forum content',
+      'delete any forum content',
+    ]);
+    $this->editOwnTopicsUser = $this->drupalCreateUser([
+      'create forum content',
+      'edit own forum content',
+      'delete own forum content',
+    ]);
+    $this->webUser = $this->drupalCreateUser();
+    $this->postCommentUser = $this->drupalCreateUser([
+      'administer content types',
+      'create forum content',
+      'post comments',
+      'skip comment approval',
+      'access comments',
+    ]);
+    $this->drupalPlaceBlock('help_block', ['region' => 'help']);
+    $this->drupalPlaceBlock('local_actions_block');
+  }
+
+  /**
+   * Tests forum functionality through the admin and user interfaces.
+   */
+  public function testForum(): void {
+    // Check that the basic forum install creates a default forum topic
+    $this->drupalGet('/forum');
+    // Look for the "General discussion" default forum
+    $this->assertSession()->linkExists('General discussion');
+    $this->assertSession()->linkByHrefExists('/forum/1');
+    // Check the presence of expected cache tags.
+    $this->assertSession()->responseHeaderContains('X-Drupal-Cache-Tags', 'config:forum.settings');
+
+    $this->drupalGet(Url::fromRoute('forum.page', ['taxonomy_term' => 1]));
+    $this->assertSession()->responseHeaderContains('X-Drupal-Cache-Tags', 'config:forum.settings');
+
+    // Do the admin tests.
+    $this->doAdminTests($this->adminUser);
+
+    // Check display order.
+    $display = EntityViewDisplay::load('node.forum.default');
+    $body = $display->getComponent('body');
+    $comment = $display->getComponent('comment_forum');
+    $taxonomy = $display->getComponent('taxonomy_forums');
+
+    // Assert field order is body » taxonomy » comments.
+    $this->assertLessThan($body['weight'], $taxonomy['weight']);
+    $this->assertLessThan($comment['weight'], $body['weight']);
+
+    // Check form order.
+    $display = EntityFormDisplay::load('node.forum.default');
+    $body = $display->getComponent('body');
+    $comment = $display->getComponent('comment_forum');
+    $taxonomy = $display->getComponent('taxonomy_forums');
+
+    // Assert category comes before body in order.
+    $this->assertLessThan($body['weight'], $taxonomy['weight']);
+
+    $this->generateForumTopics();
+
+    // Log in an unprivileged user to view the forum topics and generate an
+    // active forum topics list.
+    $this->drupalLogin($this->webUser);
+    // Verify that this user is shown a message that they may not post content.
+    $this->drupalGet('forum/' . $this->forum['tid']);
+    $this->assertSession()->pageTextContains('You are not allowed to post new content in the forum');
+
+    // Log in, and do basic tests for a user with permission to edit any forum
+    // content.
+    $this->doBasicTests($this->editAnyTopicsUser, TRUE);
+    // Create a forum node authored by this user.
+    $any_topics_user_node = $this->createForumTopic($this->forum, FALSE);
+
+    // Log in, and do basic tests for a user with permission to edit only its
+    // own forum content.
+    $this->doBasicTests($this->editOwnTopicsUser, FALSE);
+    // Create a forum node authored by this user.
+    $own_topics_user_node = $this->createForumTopic($this->forum, FALSE);
+    // Verify that this user cannot edit forum content authored by another user.
+    $this->verifyForums($any_topics_user_node, FALSE, 403);
+
+    // Verify that this user is shown a local task to add new forum content.
+    $this->drupalGet('forum');
+    $this->assertSession()->linkExists('Add new Forum topic');
+    $this->drupalGet('forum/' . $this->forum['tid']);
+    $this->assertSession()->linkExists('Add new Forum topic');
+
+    // Log in a user with permission to edit any forum content.
+    $this->drupalLogin($this->editAnyTopicsUser);
+    // Verify that this user can edit forum content authored by another user.
+    $this->verifyForums($own_topics_user_node, TRUE);
+
+    // Verify the topic and post counts on the forum page.
+    $this->drupalGet('forum');
+
+    // Find the table row for the forum that has new posts. This cannot be
+    // reliably identified by any CSS selector or its position in the table,
+    // so look for an element with the "New posts" title and traverse up the
+    // document tree until we get to the table row that contains it.
+    $row = $this->assertSession()->elementExists('css', '[title="New posts"]');
+    while ($row && $row->getTagName() !== 'tr') {
+      $row = $row->getParent();
+    }
+    $this->assertNotEmpty($row);
+    $cells = $row->findAll('css', 'td');
+    $this->assertCount(4, $cells);
+
+    // Topics cell contains number of topics (6), number of unread topics (also
+    // 6), and the forum name.
+    $this->assertEquals('6 6 new posts in forum ' . $this->forum['name'], $cells[1]->getText(), 'Number of topics found.');
+
+    // Verify total number of posts in forum.
+    $this->assertEquals('6', $cells[2]->getText(), 'Number of posts found.');
+
+    // Test loading multiple forum nodes on the front page.
+    $this->drupalLogin($this->drupalCreateUser([
+      'administer content types',
+      'create forum content',
+      'post comments',
+    ]));
+    $this->drupalGet('admin/structure/types/manage/forum');
+    $this->submitForm(['options[promote]' => 'promote'], 'Save');
+    $this->createForumTopic($this->forum, FALSE);
+    $this->createForumTopic($this->forum, FALSE);
+    $this->drupalGet('node');
+
+    // Test adding a comment to a forum topic.
+    $node = $this->createForumTopic($this->forum, FALSE);
+    $edit = [];
+    $edit['comment_body[0][value]'] = $this->randomMachineName();
+    $this->drupalGet('node/' . $node->id());
+    $this->submitForm($edit, 'Save');
+    $this->assertSession()->statusCodeEquals(200);
+
+    // Test editing a forum topic that has a comment.
+    $this->drupalLogin($this->editAnyTopicsUser);
+    $this->drupalGet('forum/' . $this->forum['tid']);
+    $this->drupalGet('node/' . $node->id() . '/edit');
+    $this->submitForm([], 'Save');
+    $this->assertSession()->statusCodeEquals(200);
+
+    // Test the root forum page title change.
+    $this->drupalGet('forum');
+    $this->assertSession()->responseHeaderContains('X-Drupal-Cache-Tags', 'config:taxonomy.vocabulary.' . $this->forum['vid']);
+    $this->assertSession()->titleEquals('Forums | Drupal');
+    $vocabulary = Vocabulary::load($this->forum['vid']);
+    $vocabulary->set('name', 'Discussions');
+    $vocabulary->save();
+    $this->drupalGet('forum');
+    $this->assertSession()->titleEquals('Discussions | Drupal');
+
+    // Test anonymous action link.
+    $this->drupalLogout();
+    $this->drupalGet('forum/' . $this->forum['tid']);
+    $this->assertSession()->linkExists('Log in to post new content in the forum.');
+  }
+
+  /**
+   * Tests that forum nodes can't be added without a parent.
+   *
+   * Verifies that forum nodes are not created without choosing "forum" from the
+   * select list.
+   */
+  public function testAddOrphanTopic(): void {
+    // Must remove forum topics to test creating orphan topics.
+    $vid = $this->config('forum.settings')->get('vocabulary');
+    $tids = \Drupal::entityQuery('taxonomy_term')
+      ->accessCheck(FALSE)
+      ->condition('vid', $vid)
+      ->execute();
+    $term_storage = \Drupal::entityTypeManager()->getStorage('taxonomy_term');
+    $terms = $term_storage->loadMultiple($tids);
+    $term_storage->delete($terms);
+
+    // Create an orphan forum item.
+    $edit = [];
+    $edit['title[0][value]'] = $this->randomMachineName(10);
+    $edit['body[0][value]'] = $this->randomMachineName(120);
+    $this->drupalLogin($this->adminUser);
+    $this->drupalGet('node/add/forum');
+    $this->submitForm($edit, 'Save');
+
+    $nid_count = $this->container->get('entity_type.manager')
+      ->getStorage('node')
+      ->getQuery()
+      ->accessCheck(FALSE)
+      ->count()
+      ->execute();
+    $this->assertEquals(0, $nid_count, 'A forum node was not created when missing a forum vocabulary.');
+
+    // Reset the defaults for future tests.
+    \Drupal::service('module_installer')->install(['forum']);
+  }
+
+  /**
+   * Runs admin tests on the admin user.
+   *
+   * @param object $user
+   *   The logged-in user.
+   */
+  private function doAdminTests($user) {
+    // Log in the user.
+    $this->drupalLogin($user);
+
+    // Add forum to the Tools menu.
+    $edit = [];
+    $this->drupalGet('admin/structure/menu/manage/tools');
+    $this->submitForm($edit, 'Save');
+    $this->assertSession()->statusCodeEquals(200);
+
+    // Edit forum taxonomy.
+    // Restoration of the settings fails and causes subsequent tests to fail.
+    $this->editForumVocabulary();
+    // Create forum container.
+    $this->forumContainer = $this->createForum('container');
+    // Verify "edit container" link exists and functions correctly.
+    $this->drupalGet('admin/structure/forum');
+    // Verify help text is shown.
+    $this->assertSession()->pageTextContains('Forums contain forum topics. Use containers to group related forums');
+    // Verify action links are there.
+    $this->assertSession()->linkExists('Add forum');
+    $this->assertSession()->linkExists('Add container');
+    $this->clickLink('edit container');
+    $this->assertSession()->pageTextContains('Edit container');
+    // Create forum inside the forum container.
+    $this->forum = $this->createForum('forum', $this->forumContainer['tid']);
+    // Verify the "edit forum" link exists and functions correctly.
+    $this->drupalGet('admin/structure/forum');
+    $this->clickLink('edit forum');
+    $this->assertSession()->pageTextContains('Edit forum');
+    // Navigate back to forum structure page.
+    $this->drupalGet('admin/structure/forum');
+    // Create second forum in container, destined to be deleted below.
+    $delete_forum = $this->createForum('forum', $this->forumContainer['tid']);
+    // Save forum overview.
+    $this->drupalGet('admin/structure/forum/');
+    $this->submitForm([], 'Save');
+    $this->assertSession()->pageTextContains('The configuration options have been saved.');
+    // Delete this second forum.
+    $this->deleteForum($delete_forum['tid']);
+    // Create forum at the top (root) level.
+    $this->rootForum = $this->createForum('forum');
+
+    // Test vocabulary form alterations.
+    $this->drupalGet('admin/structure/taxonomy/manage/forums');
+    $this->assertSession()->buttonExists('Save');
+    $this->assertSession()->buttonNotExists('Delete');
+
+    // Test term edit form alterations.
+    $this->drupalGet('taxonomy/term/' . $this->forumContainer['tid'] . '/edit');
+    // Test parent field been hidden by forum module.
+    $this->assertSession()->fieldNotExists('parent[]');
+
+    // Create a default vocabulary named "Tags".
+    $description = 'Use tags to group articles on similar topics into categories.';
+    $help = 'Enter a comma-separated list of words to describe your content.';
+    $vocabulary = Vocabulary::create([
+      'name' => 'Tags',
+      'description' => $description,
+      'vid' => 'tags',
+      'langcode' => \Drupal::languageManager()->getDefaultLanguage()->getId(),
+      'help' => $help,
+    ]);
+    $vocabulary->save();
+    // Test tags vocabulary form is not affected.
+    $this->drupalGet('admin/structure/taxonomy/manage/tags');
+    $this->assertSession()->buttonExists('Save');
+    $this->assertSession()->linkExists('Delete');
+    // Test tags vocabulary term form is not affected.
+    $this->drupalGet('admin/structure/taxonomy/manage/tags/add');
+    $this->assertSession()->fieldExists('parent[]');
+    // Test relations widget exists.
+    $this->assertSession()->elementExists('xpath', "//details[@id='edit-relations']");
+  }
+
+  /**
+   * Edits the forum taxonomy.
+   */
+  public function editForumVocabulary() {
+    // Backup forum taxonomy.
+    $vid = $this->config('forum.settings')->get('vocabulary');
+    $original_vocabulary = Vocabulary::load($vid);
+
+    // Generate a random name and description.
+    $edit = [
+      'name' => $this->randomMachineName(10),
+      'description' => $this->randomMachineName(100),
+    ];
+
+    // Edit the vocabulary.
+    $this->drupalGet('admin/structure/taxonomy/manage/' . $original_vocabulary->id());
+    $this->submitForm($edit, 'Save');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains("Updated vocabulary {$edit['name']}.");
+
+    // Grab the newly edited vocabulary.
+    $current_vocabulary = Vocabulary::load($vid);
+
+    // Make sure we actually edited the vocabulary properly.
+    $this->assertEquals($edit['name'], $current_vocabulary->label(), 'The name was updated');
+    $this->assertEquals($edit['description'], $current_vocabulary->getDescription(), 'The description was updated');
+
+    // Restore the original vocabulary's name and description.
+    $current_vocabulary->set('name', $original_vocabulary->label());
+    $current_vocabulary->set('description', $original_vocabulary->getDescription());
+    $current_vocabulary->save();
+    // Reload vocabulary to make sure changes are saved.
+    $current_vocabulary = Vocabulary::load($vid);
+    $this->assertEquals($original_vocabulary->label(), $current_vocabulary->label(), 'The original vocabulary settings were restored');
+  }
+
+  /**
+   * Creates a forum container or a forum.
+   *
+   * @param string $type
+   *   The forum type (forum container or forum).
+   * @param int $parent
+   *   The forum parent. This defaults to 0, indicating a root forum.
+   *
+   * @return \Drupal\Core\Database\StatementInterface
+   *   The created taxonomy term data.
+   */
+  public function createForum($type, $parent = 0) {
+    // Generate a random name/description.
+    $name = $this->randomMachineName(10);
+    $description = $this->randomMachineName(100);
+
+    $edit = [
+      'name[0][value]' => $name,
+      'description[0][value]' => $description,
+      'parent[0]' => $parent,
+      'weight' => '0',
+    ];
+
+    // Create forum.
+    $this->drupalGet('admin/structure/forum/add/' . $type);
+    $this->submitForm($edit, 'Save');
+    $this->assertSession()->statusCodeEquals(200);
+    $type = ($type == 'container') ? 'forum container' : 'forum';
+    $this->assertSession()->pageTextContains('Created new ' . $type . ' ' . $name . '.');
+
+    // Verify that the creation message contains a link to a term.
+    $this->assertSession()->elementExists('xpath', '//div[@data-drupal-messages]//a[contains(@href, "term/")]');
+
+    /** @var \Drupal\taxonomy\TermStorageInterface $taxonomy_term_storage */
+    $taxonomy_term_storage = $this->container->get('entity_type.manager')->getStorage('taxonomy_term');
+    // Verify forum.
+    $term = $taxonomy_term_storage->loadByProperties([
+      'vid' => $this->config('forum.settings')->get('vocabulary'),
+      'name' => $name,
+      'description__value' => $description,
+    ]);
+    $term = array_shift($term);
+    $this->assertNotEmpty($term, "The forum type '$type' should exist in the database.");
+
+    // Verify forum hierarchy.
+    $tid = $term->id();
+    $parent_tid = $taxonomy_term_storage->loadParents($tid);
+    $parent_tid = empty($parent_tid) ? 0 : array_shift($parent_tid)->id();
+    $this->assertSame($parent, $parent_tid, 'The ' . $type . ' is linked to its container');
+
+    $forum = $taxonomy_term_storage->load($tid);
+    $this->assertEquals(($type == 'forum container'), (bool) $forum->forum_container->value);
+    return [
+      'tid' => $tid,
+      'name' => $term->getName(),
+      'vid' => $term->bundle(),
+    ];
+  }
+
+  /**
+   * Deletes a forum.
+   *
+   * @param int $tid
+   *   The forum ID.
+   */
+  public function deleteForum($tid) {
+    // Delete the forum.
+    $this->drupalGet('admin/structure/forum/edit/forum/' . $tid);
+    $this->clickLink('Delete');
+    $this->assertSession()->pageTextContains('Are you sure you want to delete the forum');
+    $this->assertSession()->pageTextNotContains('Add forum');
+    $this->assertSession()->pageTextNotContains('Add forum container');
+    $this->submitForm([], 'Delete');
+
+    // Assert that the forum no longer exists.
+    $this->drupalGet('forum/' . $tid);
+    $this->assertSession()->statusCodeEquals(404);
+  }
+
+  /**
+   * Runs basic tests on the indicated user.
+   *
+   * @param \Drupal\Core\Session\AccountInterface $user
+   *   The logged in user.
+   * @param bool $admin
+   *   User has 'access administration pages' privilege.
+   */
+  private function doBasicTests($user, $admin) {
+    // Log in the user.
+    $this->drupalLogin($user);
+    // Attempt to create forum topic under a container.
+    $this->createForumTopic($this->forumContainer, TRUE);
+    // Create forum node.
+    $node = $this->createForumTopic($this->forum, FALSE);
+    // Verify the user has access to all the forum nodes.
+    $this->verifyForums($node, $admin);
+  }
+
+  /**
+   * Tests a forum with a new post displays properly.
+   */
+  public function testForumWithNewPost(): void {
+    // Log in as the first user.
+    $this->drupalLogin($this->adminUser);
+    // Create a forum container.
+    $this->forumContainer = $this->createForum('container');
+    // Create a forum.
+    $this->forum = $this->createForum('forum');
+    // Create a topic.
+    $node = $this->createForumTopic($this->forum, FALSE);
+
+    // Log in as a second user.
+    $this->drupalLogin($this->postCommentUser);
+    // Post a reply to the topic.
+    $edit = [];
+    $edit['subject[0][value]'] = $this->randomMachineName();
+    $edit['comment_body[0][value]'] = $this->randomMachineName();
+    $this->drupalGet('node/' . $node->id());
+    $this->submitForm($edit, 'Save');
+    $this->assertSession()->statusCodeEquals(200);
+
+    // Test adding a new comment.
+    $this->clickLink('Add new comment');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->fieldExists('comment_body[0][value]');
+
+    // Log in as the first user.
+    $this->drupalLogin($this->adminUser);
+    // Check that forum renders properly.
+    $this->drupalGet("forum/{$this->forum['tid']}");
+    $this->assertSession()->statusCodeEquals(200);
+
+    // Verify there is no unintentional HTML tag escaping.
+    $this->assertSession()->assertNoEscaped('<');
+  }
+
+  /**
+   * Creates a forum topic.
+   *
+   * @param array $forum
+   *   A forum array.
+   * @param bool $container
+   *   TRUE if $forum is a container; FALSE otherwise.
+   *
+   * @return object|null
+   *   The created topic node or NULL if the forum is a container.
+   */
+  public function createForumTopic($forum, $container = FALSE) {
+    // Generate a random subject/body.
+    $title = $this->randomMachineName(20);
+    $body = $this->randomMachineName(200);
+
+    $edit = [
+      'title[0][value]' => $title,
+      'body[0][value]' => $body,
+    ];
+    $tid = $forum['tid'];
+
+    // Create the forum topic, preselecting the forum ID via a URL parameter.
+    $this->drupalGet('node/add/forum', ['query' => ['forum_id' => $tid]]);
+    $this->submitForm($edit, 'Save');
+
+    if ($container) {
+      $this->assertSession()->pageTextNotContains("Forum topic $title has been created.");
+      $this->assertSession()->pageTextContains("The item {$forum['name']} is a forum container, not a forum.");
+      return;
+    }
+    else {
+      $this->assertSession()->pageTextContains("Forum topic $title has been created.");
+      $this->assertSession()->pageTextNotContains("The item {$forum['name']} is a forum container, not a forum.");
+
+      // Verify that the creation message contains a link to a node.
+      $this->assertSession()->elementExists('xpath', '//div[@data-drupal-messages]//a[contains(@href, "node/")]');
+    }
+
+    // Retrieve node object, ensure that the topic was created and in the proper forum.
+    $node = $this->drupalGetNodeByTitle($title);
+    $this->assertNotNull($node, "Node $title was loaded");
+    $this->assertEquals($tid, $node->taxonomy_forums->target_id, 'Saved forum topic was in the expected forum');
+
+    // View forum topic.
+    $this->drupalGet('node/' . $node->id());
+    $this->assertSession()->pageTextContains($title);
+    $this->assertSession()->pageTextContains($body);
+
+    return $node;
+  }
+
+  /**
+   * Verifies that the logged in user has access to a forum node.
+   *
+   * @param \Drupal\Core\Entity\EntityInterface $node
+   *   The node being checked.
+   * @param bool $admin
+   *   Boolean to indicate whether the user can 'access administration pages'.
+   * @param int $response
+   *   The expected HTTP response code.
+   */
+  private function verifyForums(EntityInterface $node, $admin, $response = 200) {
+    $response2 = ($admin) ? 200 : 403;
+
+    // View forum help node.
+    $this->drupalGet('admin/help/forum');
+    $this->assertSession()->statusCodeEquals($response2);
+    if ($response2 == 200) {
+      $this->assertSession()->titleEquals('Forum | Drupal');
+      $this->assertSession()->pageTextContains('Forum');
+    }
+
+    // View forum container page.
+    $this->verifyForumView($this->forumContainer);
+    // View forum page.
+    $this->verifyForumView($this->forum, $this->forumContainer);
+    // View root forum page.
+    $this->verifyForumView($this->rootForum);
+
+    // View forum node.
+    $this->drupalGet('node/' . $node->id());
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->titleEquals($node->label() . ' | Drupal');
+    $breadcrumb_build = [
+      Link::createFromRoute('Home', '<front>'),
+      Link::createFromRoute('Forums', 'forum.index'),
+      Link::createFromRoute($this->forumContainer['name'], 'forum.page', ['taxonomy_term' => $this->forumContainer['tid']]),
+      Link::createFromRoute($this->forum['name'], 'forum.page', ['taxonomy_term' => $this->forum['tid']]),
+    ];
+    $breadcrumb = [
+      '#theme' => 'breadcrumb',
+      '#links' => $breadcrumb_build,
+    ];
+    $this->assertSession()->responseContains(\Drupal::service('renderer')->renderRoot($breadcrumb));
+
+    // View forum edit node.
+    $this->drupalGet('node/' . $node->id() . '/edit');
+    $this->assertSession()->statusCodeEquals($response);
+    if ($response == 200) {
+      $this->assertSession()->titleEquals('Edit Forum topic ' . $node->label() . ' | Drupal');
+    }
+
+    if ($response == 200) {
+      // Edit forum node (including moving it to another forum).
+      $edit = [];
+      $edit['title[0][value]'] = 'node/' . $node->id();
+      $edit['body[0][value]'] = $this->randomMachineName(256);
+      // Assume the topic is initially associated with $forum.
+      $edit['taxonomy_forums'] = $this->rootForum['tid'];
+      $edit['shadow'] = TRUE;
+      $this->drupalGet('node/' . $node->id() . '/edit');
+      $this->submitForm($edit, 'Save');
+      $this->assertSession()->pageTextContains('Forum topic ' . $edit['title[0][value]'] . ' has been updated.');
+
+      // Verify topic was moved to a different forum.
+      $forum_tid = $this->container
+        ->get('database')
+        ->select('forum', 'f')
+        ->fields('f', ['tid'])
+        ->condition('nid', $node->id())
+        ->condition('vid', $node->getRevisionId())
+        ->execute()
+        ->fetchField();
+      $this->assertSame($this->rootForum['tid'], $forum_tid, 'The forum topic is linked to a different forum');
+
+      // Delete forum node.
+      $this->drupalGet('node/' . $node->id() . '/delete');
+      $this->submitForm([], 'Delete');
+      $this->assertSession()->statusCodeEquals($response);
+      $this->assertSession()->pageTextContains("Forum topic {$edit['title[0][value]']} has been deleted.");
+    }
+  }
+
+  /**
+   * Verifies the display of a forum page.
+   *
+   * @param array $forum
+   *   A row from the taxonomy_term_data table in an array.
+   * @param array $parent
+   *   (optional) An array representing the forum's parent.
+   */
+  private function verifyForumView($forum, $parent = NULL) {
+    // View forum page.
+    $this->drupalGet('forum/' . $forum['tid']);
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->titleEquals($forum['name'] . ' | Drupal');
+
+    $breadcrumb_build = [
+      Link::createFromRoute('Home', '<front>'),
+      Link::createFromRoute('Forums', 'forum.index'),
+    ];
+    if (isset($parent)) {
+      $breadcrumb_build[] = Link::createFromRoute($parent['name'], 'forum.page', ['taxonomy_term' => $parent['tid']]);
+    }
+
+    $breadcrumb = [
+      '#theme' => 'breadcrumb',
+      '#links' => $breadcrumb_build,
+    ];
+    $this->assertSession()->responseContains(\Drupal::service('renderer')->renderRoot($breadcrumb));
+  }
+
+  /**
+   * Generates forum topics.
+   */
+  private function generateForumTopics() {
+    $this->nids = [];
+    for ($i = 0; $i < 5; $i++) {
+      $node = $this->createForumTopic($this->forum, FALSE);
+      $this->nids[] = $node->id();
+    }
+  }
+
+  /**
+   * Evaluate whether "Add new Forum topic" button is present or not.
+   */
+  public function testForumTopicButton(): void {
+    $this->drupalLogin($this->adminUser);
+
+    // Validate that link doesn't exist on the forum container page.
+    $forum_container = $this->createForum('container');
+    $this->drupalGet('forum/' . $forum_container['tid']);
+    $this->assertSession()->linkNotExists('Add new Forum topic');
+
+    // Validate that link exists on forum page.
+    $forum = $this->createForum('forum');
+    $this->drupalGet('forum/' . $forum['tid']);
+    $this->assertSession()->linkExists('Add new Forum topic');
+  }
+
+}

core/modules/forum/tests/src/Functional/ForumUninstallTest.php

@@ -0,0 +1,189 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Functional;
+
+use Drupal\comment\CommentInterface;
+use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\node\Entity\NodeType;
+use Drupal\comment\Entity\Comment;
+use Drupal\taxonomy\Entity\Term;
+use Drupal\taxonomy\Entity\Vocabulary;
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests forum module uninstallation.
+ *
+ * @group forum
+ * @group legacy
+ * @group #slow
+ */
+class ForumUninstallTest extends BrowserTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  protected static $modules = ['forum'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Tests if forum module uninstallation properly deletes the field.
+   */
+  public function testForumUninstallWithField(): void {
+    $this->drupalLogin($this->drupalCreateUser([
+      'administer taxonomy',
+      'administer nodes',
+      'administer modules',
+      'delete any forum content',
+      'administer content types',
+    ]));
+    // Ensure that the field exists before uninstallation.
+    $field_storage = FieldStorageConfig::loadByName('node', 'taxonomy_forums');
+    $this->assertNotNull($field_storage, 'The taxonomy_forums field storage exists.');
+
+    // Create a taxonomy term.
+    $term = Term::create([
+      'name' => 'A term',
+      'langcode' => \Drupal::languageManager()->getDefaultLanguage()->getId(),
+      'description' => '',
+      'parent' => [0],
+      'vid' => 'forums',
+      'forum_container' => 0,
+    ]);
+    $term->save();
+
+    // Create a forum node.
+    $node = $this->drupalCreateNode([
+      'title' => 'A forum post',
+      'type' => 'forum',
+      'taxonomy_forums' => [['target_id' => $term->id()]],
+    ]);
+
+    // Create at least one comment against the forum node.
+    $comment = Comment::create([
+      'entity_id' => $node->nid->value,
+      'entity_type' => 'node',
+      'field_name' => 'comment_forum',
+      'pid' => 0,
+      'uid' => 0,
+      'status' => CommentInterface::PUBLISHED,
+      'subject' => $this->randomMachineName(),
+      'hostname' => '127.0.0.1',
+    ]);
+    $comment->save();
+
+    // Attempt to uninstall forum.
+    $this->drupalGet('admin/modules/uninstall');
+    // Assert forum is required.
+    $this->assertSession()->fieldDisabled('uninstall[forum]');
+    $this->assertSession()->pageTextContains('To uninstall Forum, first delete all Forum content');
+
+    // Delete the node.
+    $this->drupalGet('node/' . $node->id() . '/delete');
+    $this->submitForm([], 'Delete');
+
+    // Attempt to uninstall forum.
+    $this->drupalGet('admin/modules/uninstall');
+    // Assert forum is still required.
+    $this->assertSession()->fieldDisabled('uninstall[forum]');
+    $this->assertSession()->pageTextContains('To uninstall Forum, first delete all Forums terms');
+
+    // Delete any forum terms.
+    $vid = $this->config('forum.settings')->get('vocabulary');
+    $storage = \Drupal::entityTypeManager()->getStorage('taxonomy_term');
+    $terms = $storage->loadByProperties(['vid' => $vid]);
+    $storage->delete($terms);
+
+    // Ensure that the forum node type can not be deleted.
+    $this->drupalGet('admin/structure/types/manage/forum');
+    $this->assertSession()->linkNotExists('Delete');
+
+    // Now attempt to uninstall forum.
+    $this->drupalGet('admin/modules/uninstall');
+    // Assert forum is no longer required.
+    $this->assertSession()->fieldExists('uninstall[forum]');
+    $this->drupalGet('admin/modules/uninstall');
+    $this->submitForm(['uninstall[forum]' => 1], 'Uninstall');
+    $this->submitForm([], 'Uninstall');
+
+    // Check that the field is now deleted.
+    $field_storage = FieldStorageConfig::loadByName('node', 'taxonomy_forums');
+    $this->assertNull($field_storage, 'The taxonomy_forums field storage has been deleted.');
+
+    // Check that a node type with a machine name of forum can be created after
+    // uninstalling the forum module and the node type is not locked.
+    $edit = [
+      'name' => 'Forum',
+      'title_label' => 'title for forum',
+      'type' => 'forum',
+    ];
+    $this->drupalGet('admin/structure/types/add');
+    $this->submitForm($edit, 'Save');
+    $this->assertTrue((bool) NodeType::load('forum'), 'Node type with machine forum created.');
+    $this->drupalGet('admin/structure/types/manage/forum');
+    $this->clickLink('Delete');
+    $this->submitForm([], 'Delete');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertFalse((bool) NodeType::load('forum'), 'Node type with machine forum deleted.');
+
+    // Double check everything by reinstalling the forum module again.
+    $this->drupalGet('admin/modules');
+    $this->submitForm(['modules[forum][enable]' => 1], 'Install');
+    $this->submitForm([], 'Continue');
+    $this->assertSession()->pageTextContains('Module Forum has been installed.');
+  }
+
+  /**
+   * Tests uninstallation if the field storage has been deleted beforehand.
+   */
+  public function testForumUninstallWithoutFieldStorage(): void {
+    // Manually delete the taxonomy_forums field before module uninstallation.
+    $field_storage = FieldStorageConfig::loadByName('node', 'taxonomy_forums');
+    $this->assertNotNull($field_storage, 'The taxonomy_forums field storage exists.');
+    $field_storage->delete();
+
+    // Check that the field is now deleted.
+    $field_storage = FieldStorageConfig::loadByName('node', 'taxonomy_forums');
+    $this->assertNull($field_storage, 'The taxonomy_forums field storage has been deleted.');
+
+    // Delete all terms in the Forums vocabulary. Uninstalling the forum module
+    // will fail unless this is done.
+    $terms = \Drupal::entityTypeManager()->getStorage('taxonomy_term')->loadByProperties(['vid' => 'forums']);
+    foreach ($terms as $term) {
+      $term->delete();
+    }
+
+    // Ensure that uninstallation succeeds even if the field has already been
+    // deleted manually beforehand.
+    $this->container->get('module_installer')->uninstall(['forum']);
+  }
+
+  /**
+   * Tests uninstallation of forum module when vocabulary is deleted.
+   */
+  public function testForumUninstallWithoutForumVocabulary(): void {
+    $this->drupalLogin($this->drupalCreateUser([
+      'administer modules',
+    ]));
+    Vocabulary::load('forums')->delete();
+
+    // Now attempt to uninstall forum.
+    $this->drupalGet('admin/modules/uninstall');
+    $this->assertSession()->responseNotContains('The website encountered an unexpected error. Try again later');
+    $this->assertSession()->statusCodeEquals(200);
+
+    // Assert forum is no longer required.
+    $this->assertSession()->fieldExists('uninstall[forum]');
+
+    $this->drupalGet('admin/modules/uninstall');
+    $this->submitForm(['uninstall[forum]' => 1], 'Uninstall');
+  }
+
+}

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

@@ -0,0 +1,26 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Functional;
+
+use Drupal\Tests\system\Functional\Module\GenericModuleTestBase;
+
+/**
+ * Generic module test for forum.
+ *
+ * @group forum
+ * @group legacy
+ */
+class GenericTest extends GenericModuleTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function preUninstallSteps(): void {
+    $storage = \Drupal::entityTypeManager()->getStorage('taxonomy_term');
+    $terms = $storage->loadMultiple();
+    $storage->delete($terms);
+  }
+
+}

core/modules/forum/tests/src/Functional/Module/DependencyTest.php

@@ -0,0 +1,62 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Functional\Module;
+
+use Drupal\Tests\system\Functional\Module\ModuleTestBase;
+
+/**
+ * Enable module without dependency enabled.
+ *
+ * @group form
+ * @group legacy
+ */
+class DependencyTest extends ModuleTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Tests attempting to uninstall a module that has installed dependents.
+   */
+  public function testUninstallDependents(): void {
+    // Enable the forum module.
+    $edit = ['modules[forum][enable]' => 'forum'];
+    $this->drupalGet('admin/modules');
+    $this->submitForm($edit, 'Install');
+    $this->submitForm([], 'Continue');
+    $this->assertModules(['forum'], TRUE);
+
+    // Check that the comment module cannot be uninstalled.
+    $this->drupalGet('admin/modules/uninstall');
+    $this->assertSession()->fieldDisabled('uninstall[comment]');
+
+    // Delete any forum terms.
+    $vid = $this->config('forum.settings')->get('vocabulary');
+    // Ensure taxonomy has been loaded into the test-runner after forum was
+    // enabled.
+    \Drupal::moduleHandler()->load('taxonomy');
+    $storage = \Drupal::entityTypeManager()->getStorage('taxonomy_term');
+    $terms = $storage->loadByProperties(['vid' => $vid]);
+    $storage->delete($terms);
+
+    // Uninstall the forum module, and check that taxonomy now can also be
+    // uninstalled.
+    $edit = ['uninstall[forum]' => 'forum'];
+    $this->drupalGet('admin/modules/uninstall');
+    $this->submitForm($edit, 'Uninstall');
+    $this->submitForm([], 'Uninstall');
+    $this->assertSession()->pageTextContains('The selected modules have been uninstalled.');
+
+    // Uninstall comment module.
+    $edit = ['uninstall[comment]' => 'comment'];
+    $this->drupalGet('admin/modules/uninstall');
+    $this->submitForm($edit, 'Uninstall');
+    $this->submitForm([], 'Uninstall');
+    $this->assertSession()->pageTextContains('The selected modules have been uninstalled.');
+  }
+
+}

core/modules/forum/tests/src/Functional/NodeAccessPagerTest.php

@@ -0,0 +1,79 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests access controlled node views have the right amount of comment pages.
+ *
+ * @group form
+ * @group legacy
+ */
+class NodeAccessPagerTest extends BrowserTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  protected static $modules = ['node_access_test', 'forum'];
+
+  /**
+   * A user account to use for the test.
+   *
+   * @var \Drupal\user\Entity\User
+   */
+  protected $webUser;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  protected function setUp(): void {
+    parent::setUp();
+
+    node_access_rebuild();
+    $this->drupalCreateContentType(['type' => 'page', 'name' => 'Basic page']);
+    $this->webUser = $this->drupalCreateUser([
+      'access content',
+      'node test view',
+    ]);
+  }
+
+  /**
+   * Tests the forum node pager for nodes with multiple grants per realm.
+   */
+  public function testForumPager(): void {
+    // Look up the forums vocabulary ID.
+    $vid = $this->config('forum.settings')->get('vocabulary');
+    $this->assertNotEmpty($vid, 'Forum navigation vocabulary ID is set.');
+
+    // Look up the general discussion term.
+    $tree = \Drupal::entityTypeManager()->getStorage('taxonomy_term')->loadTree($vid, 0, 1);
+    $tid = reset($tree)->tid;
+    $this->assertNotEmpty($tid, 'General discussion term is found in the forum vocabulary.');
+
+    // Create 30 nodes.
+    for ($i = 0; $i < 30; $i++) {
+      $this->drupalCreateNode([
+        'nid' => NULL,
+        'type' => 'forum',
+        'taxonomy_forums' => [
+          ['target_id' => $tid],
+        ],
+      ]);
+    }
+
+    // View the general discussion forum page. With the default 25 nodes per
+    // page there should be two pages for 30 nodes, no more.
+    $this->drupalLogin($this->webUser);
+    $this->drupalGet('forum/' . $tid);
+    $this->assertSession()->responseContains('page=1');
+    $this->assertSession()->responseNotContains('page=2');
+  }
+
+}

core/modules/forum/tests/src/Functional/UrlAlterFunctionalTest.php

@@ -0,0 +1,87 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Functional;
+
+use Drupal\Core\Database\Database;
+use Drupal\Tests\BrowserTestBase;
+use Drupal\taxonomy\Entity\Term;
+
+/**
+ * Tests altering the inbound path and the outbound path.
+ *
+ * @group form
+ * @group legacy
+ */
+class UrlAlterFunctionalTest extends BrowserTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  protected static $modules = ['path', 'forum', 'forum_url_alter_test'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Tests that URL altering works and that it occurs in the correct order.
+   */
+  public function testUrlAlter(): void {
+    // Ensure that the path_alias table exists after Drupal installation.
+    $this->assertTrue(Database::getConnection()->schema()->tableExists('path_alias'), 'The path_alias table exists after Drupal installation.');
+
+    // Test that 'forum' is altered to 'community' correctly, both at the root
+    // level and for a specific existing forum.
+    $this->drupalGet('community');
+    $this->assertSession()->pageTextContains('General discussion');
+    $this->assertUrlOutboundAlter('/forum', '/community');
+    $forum_vid = $this->config('forum.settings')->get('vocabulary');
+    $term_name = $this->randomMachineName();
+    $term = Term::create([
+      'name' => $term_name,
+      'vid' => $forum_vid,
+    ]);
+    $term->save();
+    $this->drupalGet("community/" . $term->id());
+    $this->assertSession()->pageTextContains($term_name);
+    $this->assertUrlOutboundAlter("/forum/" . $term->id(), "/community/" . $term->id());
+  }
+
+  /**
+   * Assert that an outbound path is altered to an expected value.
+   *
+   * @param string $original
+   *   A string with the original path that is run through generateFrommPath().
+   * @param string $final
+   *   A string with the expected result after generateFrommPath().
+   *
+   * @internal
+   */
+  protected function assertUrlOutboundAlter(string $original, string $final): void {
+    // Test outbound altering.
+    $result = $this->container->get('path_processor_manager')->processOutbound($original);
+    $this->assertSame($final, $result, "Altered outbound URL $original, expected $final, and got $result.");
+  }
+
+  /**
+   * Assert that an inbound path is altered to an expected value.
+   *
+   * @param string $original
+   *   The original path before it has been altered by inbound URL processing.
+   * @param string $final
+   *   A string with the expected result.
+   *
+   * @internal
+   */
+  protected function assertUrlInboundAlter(string $original, string $final): void {
+    // Test inbound altering.
+    $result = $this->container->get('path_alias.manager')->getPathByAlias($original);
+    $this->assertSame($final, $result, "Altered inbound URL $original, expected $final, and got $result.");
+  }
+
+}

core/modules/forum/tests/src/Functional/Views/ForumIntegrationTest.php

@@ -0,0 +1,102 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Functional\Views;
+
+use Drupal\node\NodeInterface;
+use Drupal\views\Views;
+use Drupal\Tests\views\Functional\ViewTestBase;
+
+/**
+ * Tests the forum integration into views.
+ *
+ * @group forum
+ * @group legacy
+ */
+class ForumIntegrationTest extends ViewTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  protected static $modules = ['forum_test_views'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Views used by this test.
+   *
+   * @var array
+   */
+  public static $testViews = ['test_forum_index'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp($import_test_views = TRUE, $modules = ['forum_test_views']): void {
+    parent::setUp($import_test_views, $modules);
+  }
+
+  /**
+   * Tests the integration.
+   */
+  public function testForumIntegration(): void {
+    // Create a forum.
+    $entity_type_manager = $this->container->get('entity_type.manager');
+    $term = $entity_type_manager->getStorage('taxonomy_term')->create(['vid' => 'forums', 'name' => $this->randomMachineName()]);
+    $term->save();
+
+    $comment_storage = $entity_type_manager->getStorage('comment');
+
+    // Create some nodes which are part of this forum with some comments.
+    $nodes = [];
+    for ($i = 0; $i < 3; $i++) {
+      $node = $this->drupalCreateNode(['type' => 'forum', 'taxonomy_forums' => [$term->id()], 'sticky' => $i == 0 ? NodeInterface::STICKY : NodeInterface::NOT_STICKY]);
+      $nodes[] = $node;
+    }
+
+    $account = $this->drupalCreateUser(['skip comment approval']);
+    $this->drupalLogin($account);
+
+    $comments = [];
+    foreach ($nodes as $index => $node) {
+      for ($i = 0; $i <= $index; $i++) {
+        $comment = $comment_storage->create(['entity_type' => 'node', 'entity_id' => $node->id(), 'field_name' => 'comment_forum']);
+        $comment->save();
+        $comments[$comment->get('entity_id')->target_id][$comment->id()] = $comment;
+      }
+    }
+
+    $view = Views::getView('test_forum_index');
+    $this->executeView($view);
+
+    $expected_result = [];
+    $expected_result[] = [
+      'nid' => $nodes[0]->id(),
+      'sticky' => NodeInterface::STICKY,
+      'comment_count' => 1.,
+    ];
+    $expected_result[] = [
+      'nid' => $nodes[1]->id(),
+      'sticky' => NodeInterface::NOT_STICKY,
+      'comment_count' => 2.,
+    ];
+    $expected_result[] = [
+      'nid' => $nodes[2]->id(),
+      'sticky' => NodeInterface::NOT_STICKY,
+      'comment_count' => 3.,
+    ];
+    $column_map = [
+      'nid' => 'nid',
+      'forum_index_sticky' => 'sticky',
+      'forum_index_comment_count' => 'comment_count',
+    ];
+    $this->assertIdenticalResultset($view, $expected_result, $column_map);
+  }
+
+}

core/modules/forum/tests/src/Functional/migrate_drupal/d6/NoMultilingualReviewPageTest.php

@@ -0,0 +1,77 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Functional\migrate_drupal\d6;
+
+use Drupal\Tests\migrate_drupal_ui\Functional\NoMultilingualReviewPageTestBase;
+
+/**
+ * Tests migrate upgrade review page.
+ *
+ * @group forum
+ * @group legacy
+ */
+class NoMultilingualReviewPageTest extends NoMultilingualReviewPageTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'forum',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->loadFixture($this->getModulePath('forum') . '/tests/fixtures/drupal6.php');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getSourceBasePath() {
+    return __DIR__;
+  }
+
+  /**
+   * Tests that Forum is displayed in the will be upgraded list.
+   */
+  public function testMigrateUpgradeReviewPage(): void {
+    $this->prepare();
+    // Start the upgrade process.
+    $this->submitCredentialForm();
+
+    $session = $this->assertSession();
+    $this->submitForm([], 'I acknowledge I may lose data. Continue anyway.');
+    $session->statusCodeEquals(200);
+
+    // Confirm that Forum will be upgraded.
+    $session->elementExists('xpath', "//td[contains(@class, 'checked') and text() = 'Forum']");
+    $session->elementNotExists('xpath', "//td[contains(@class, 'error') and text() = 'Forum']");
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getAvailablePaths() {
+    return [];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getIncompletePaths() {
+    return [];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getMissingPaths() {
+    return [];
+  }
+
+}

core/modules/forum/tests/src/Functional/migrate_drupal/d6/Upgrade6Test.php

@@ -0,0 +1,155 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Functional\migrate_drupal\d6;
+
+use Drupal\Tests\migrate_drupal_ui\Functional\MigrateUpgradeExecuteTestBase;
+
+/**
+ * Tests Drupal 6 upgrade using the migrate UI.
+ *
+ * The test method is provided by the MigrateUpgradeTestBase class.
+ *
+ * @group forum
+ * @group #slow
+ * @group legacy
+ */
+class Upgrade6Test extends MigrateUpgradeExecuteTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'forum',
+    'migrate_drupal_ui',
+  ];
+
+  /**
+   * The entity storage for node.
+   *
+   * @var \Drupal\Core\Entity\EntityStorageInterface
+   */
+  protected $nodeStorage;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->loadFixture($this->getModulePath('forum') . '/tests/fixtures/drupal6.php');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getSourceBasePath() {
+    return __DIR__ . '/files';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getEntityCounts() {
+    return [
+      'action' => 24,
+      'base_field_override' => 22,
+      'block' => 33,
+      'block_content' => 1,
+      'block_content_type' => 1,
+      'comment' => 4,
+      'comment_type' => 8,
+      'contact_form' => 2,
+      'contact_message' => 0,
+      'date_format' => 12,
+      'editor' => 2,
+      'entity_form_display' => 18,
+      'entity_form_mode' => 1,
+      'entity_view_display' => 34,
+      'entity_view_mode' => 11,
+      'field_config' => 41,
+      'field_storage_config' => 25,
+      'file' => 1,
+      'filter_format' => 7,
+      'image_style' => 6,
+      'menu' => 8,
+      'menu_link_content' => 1,
+      'node' => 3,
+      'node_type' => 7,
+      'path_alias' => 4,
+      'search_page' => 3,
+      'shortcut' => 2,
+      'shortcut_set' => 1,
+      'taxonomy_term' => 7,
+      'taxonomy_vocabulary' => 4,
+      'user' => 3,
+      'user_role' => 4,
+      'view' => 14,
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getEntityCountsIncremental() {
+    return [];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getAvailablePaths() {
+    return [
+      'Block',
+      'Comment',
+      'Content',
+      'Date',
+      'Date API',
+      'Date Timezone',
+      'Email',
+      'Event',
+      'FileField',
+      'Filter',
+      'Forum',
+      'ImageAPI',
+      'ImageCache',
+      'ImageField',
+      'Menu',
+      'Node',
+      'Path',
+      'Search',
+      'System',
+      'Taxonomy',
+      'Text',
+      'Upload',
+      'User',
+      'Variable admin',
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getMissingPaths() {
+    return [];
+  }
+
+  /**
+   * Executes all steps of migrations upgrade.
+   */
+  public function testUpgrade(): void {
+    // Start the upgrade process.
+    $this->submitCredentialForm();
+    $session = $this->assertSession();
+
+    $this->submitForm([], 'I acknowledge I may lose data. Continue anyway.');
+    $session->statusCodeEquals(200);
+
+    // Test the review form.
+    $this->assertReviewForm();
+
+    $this->submitForm([], 'Perform upgrade');
+    $this->assertUpgrade($this->getEntityCounts());
+  }
+
+}

core/modules/forum/tests/src/Functional/migrate_drupal/d6/files/test.txt

@@ -0,0 +1 @@
+0

core/modules/forum/tests/src/Functional/migrate_drupal/d7/NoMultilingualReviewPageTest.php

@@ -0,0 +1,79 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Functional\migrate_drupal\d7;
+
+use Drupal\Tests\migrate_drupal_ui\Functional\NoMultilingualReviewPageTestBase;
+
+/**
+ * Tests Drupal 7 upgrade without translations.
+ *
+ * The test method is provided by the MigrateUpgradeTestBase class.
+ *
+ * @group forum
+ * @group legacy
+ */
+class NoMultilingualReviewPageTest extends NoMultilingualReviewPageTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'forum',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->loadFixture($this->getModulePath('forum') . '/tests/fixtures/drupal7.php');
+  }
+
+  /**
+   * Tests that Forum is displayed in the will be upgraded list.
+   */
+  public function testMigrateUpgradeReviewPage(): void {
+    $this->prepare();
+    // Start the upgrade process.
+    $this->submitCredentialForm();
+
+    $session = $this->assertSession();
+    $this->submitForm([], 'I acknowledge I may lose data. Continue anyway.');
+    $session->statusCodeEquals(200);
+
+    // Confirm that Forum will be upgraded.
+    $session->elementExists('xpath', "//td[contains(@class, 'checked') and text() = 'Forum']");
+    $session->elementNotExists('xpath', "//td[contains(@class, 'error') and text() = 'Forum']");
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getSourceBasePath() {
+    return __DIR__ . '/files';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getAvailablePaths() {
+    return [];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getIncompletePaths() {
+    return [];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getMissingPaths() {
+    return [];
+  }
+
+}

core/modules/forum/tests/src/Functional/migrate_drupal/d7/Upgrade7Test.php

@@ -0,0 +1,172 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Functional\migrate_drupal\d7;
+
+use Drupal\Tests\migrate_drupal_ui\Functional\MigrateUpgradeExecuteTestBase;
+
+/**
+ * Tests Drupal 7 upgrade using the migrate UI.
+ *
+ * The test method is provided by the MigrateUpgradeTestBase class.
+ *
+ * @group forum
+ * @group #slow
+ * @group legacy
+ */
+class Upgrade7Test extends MigrateUpgradeExecuteTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'forum',
+    'migrate_drupal_ui',
+  ];
+
+  /**
+   * The entity storage for node.
+   *
+   * @var \Drupal\Core\Entity\EntityStorageInterface
+   */
+  protected $nodeStorage;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // @todo remove in https://www.drupal.org/project/drupal/issues/3267040
+    // Delete the existing content made to test the ID Conflict form. Migrations
+    // are to be done on a site without content. The test of the ID Conflict
+    // form is being moved to its own issue which will remove the deletion
+    // of the created nodes.
+    // See https://www.drupal.org/project/drupal/issues/3087061.
+    $this->nodeStorage = $this->container->get('entity_type.manager')
+      ->getStorage('node');
+    $this->nodeStorage->delete($this->nodeStorage->loadMultiple());
+
+    $this->loadFixture($this->getModulePath('forum') . '/tests/fixtures/drupal7.php');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getSourceBasePath() {
+    return __DIR__ . '/files';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getEntityCounts() {
+    return [
+      'action' => 24,
+      'base_field_override' => 3,
+      'block' => 26,
+      'block_content' => 1,
+      'block_content_type' => 1,
+      'comment' => 0,
+      'comment_type' => 7,
+      'contact_form' => 2,
+      'contact_message' => 0,
+      'date_format' => 12,
+      'editor' => 2,
+      'entity_form_display' => 16,
+      'entity_form_mode' => 1,
+      'entity_view_display' => 24,
+      'entity_view_mode' => 11,
+      'field_config' => 26,
+      'field_storage_config' => 16,
+      'file' => 1,
+      'filter_format' => 7,
+      'image_style' => 7,
+      'menu' => 5,
+      'menu_link_content' => 3,
+      'node' => 2,
+      'node_type' => 6,
+      'path_alias' => 1,
+      'search_page' => 3,
+      'shortcut' => 2,
+      'shortcut_set' => 1,
+      'taxonomy_term' => 6,
+      'taxonomy_vocabulary' => 2,
+      'user' => 4,
+      'user_role' => 4,
+      'view' => 14,
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getEntityCountsIncremental() {
+    return [];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getAvailablePaths() {
+    return [
+      'Block',
+      'Comment',
+      'Content translation',
+      'Date',
+      'Field SQL storage',
+      'Field',
+      'File',
+      'Filter',
+      'Forum',
+      'Image',
+      'Menu',
+      'Node',
+      'Options',
+      'Path',
+      'Search',
+      'System',
+      'Taxonomy',
+      'Text',
+      'User',
+      'Contextual links',
+      'Date API',
+      'Field UI',
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getMissingPaths() {
+    return [
+      'Locale',
+      'Entity Translation',
+      'Internationalization',
+      'String translation',
+      'Taxonomy translation',
+      'Translation sets',
+      'Variable',
+    ];
+  }
+
+  /**
+   * Executes all steps of migrations upgrade.
+   */
+  public function testUpgrade(): void {
+    // Start the upgrade process.
+    $this->submitCredentialForm();
+    $session = $this->assertSession();
+
+    $this->submitForm([], 'I acknowledge I may lose data. Continue anyway.');
+    $session->statusCodeEquals(200);
+
+    // Test the review form.
+    $this->assertReviewForm();
+
+    $this->submitForm([], 'Perform upgrade');
+    $this->assertUpgrade($this->getEntityCounts());
+  }
+
+}

core/modules/forum/tests/src/Functional/migrate_drupal/d7/files/test.txt

@@ -0,0 +1 @@
+0

core/modules/forum/tests/src/Kernel/ForumIndexTest.php

@@ -0,0 +1,56 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Kernel;
+
+use Drupal\KernelTests\KernelTestBase;
+
+/**
+ * Defines a class for testing the forum_index table.
+ *
+ * @group forum
+ */
+final class ForumIndexTest extends KernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'system',
+    'user',
+    'node',
+    'history',
+    'taxonomy',
+    'forum',
+    'comment',
+    'options',
+    'text',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->installEntitySchema('node');
+    $this->installEntitySchema('user');
+    $this->installEntitySchema('comment');
+    $this->installEntitySchema('taxonomy_term');
+    $this->installSchema('forum', ['forum_index']);
+  }
+
+  /**
+   * Tests there's a primary key on the forum_index table.
+   */
+  public function testForumIndexIndex(): void {
+    $schema = \Drupal::database()->schema();
+    $this->assertTrue($schema->tableExists('forum_index'));
+    // We can't reliably call ::indexExists for each database driver as sqlite
+    // doesn't have named indexes for primary keys like mysql (PRIMARY) and
+    // pgsql (pkey).
+    $find_primary_key_columns = new \ReflectionMethod(get_class($schema), 'findPrimaryKeyColumns');
+    $this->assertEquals(['nid', 'tid'], $find_primary_key_columns->invoke($schema, 'forum_index'));
+  }
+
+}

core/modules/forum/tests/src/Kernel/ForumValidationTest.php

@@ -0,0 +1,74 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Kernel;
+
+use Drupal\KernelTests\Core\Entity\EntityKernelTestBase;
+use Drupal\node\Entity\Node;
+use Drupal\taxonomy\Entity\Term;
+
+/**
+ * Tests forum validation constraints.
+ *
+ * @group forum
+ * @group legacy
+ */
+class ForumValidationTest extends EntityKernelTestBase {
+
+  /**
+   * Modules to install.
+   *
+   * @var array
+   */
+  protected static $modules = [
+    'node',
+    'options',
+    'comment',
+    'taxonomy',
+    'forum',
+  ];
+
+  /**
+   * Tests the forum validation constraints.
+   */
+  public function testValidation(): void {
+    $this->installConfig('forum');
+
+    // Add a forum.
+    $forum = Term::create([
+      'name' => 'forum 1',
+      'vid' => 'forums',
+      'forum_container' => 0,
+    ]);
+
+    // Add a container.
+    $container = Term::create([
+      'name' => 'container 1',
+      'vid' => 'forums',
+      'forum_container' => 1,
+    ]);
+
+    // Add a forum post.
+    $forum_post = Node::create([
+      'type' => 'forum',
+      'title' => 'Do these pants make my butt look big?',
+    ]);
+
+    $violations = $forum_post->validate();
+    $this->assertCount(1, $violations);
+    $this->assertEquals('This value should not be null.', $violations[0]->getMessage());
+
+    // Add the forum term.
+    $forum_post->set('taxonomy_forums', $forum);
+    $violations = $forum_post->validate();
+    $this->assertCount(0, $violations);
+
+    // Try to use a container.
+    $forum_post->set('taxonomy_forums', $container);
+    $violations = $forum_post->validate();
+    $this->assertCount(1, $violations);
+    $this->assertEquals(sprintf('The item %s is a forum container, not a forum. Select one of the forums below instead.', $container->label()), $violations[0]->getMessage());
+  }
+
+}

core/modules/forum/tests/src/Kernel/Migrate/MigrateTestTrait.php

@@ -0,0 +1,105 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Kernel\Migrate;
+
+use Drupal\taxonomy\Entity\Term;
+use Drupal\taxonomy\TermInterface;
+
+/**
+ * Common assertions for migration tests.
+ */
+trait MigrateTestTrait {
+
+  /**
+   * The cached taxonomy tree items, keyed by vid and tid.
+   *
+   * @var array
+   */
+  protected $treeData = [];
+
+  /**
+   * Validate a migrated term contains the expected values.
+   *
+   * @param int $id
+   *   Entity ID to load and check.
+   * @param string $expected_language
+   *   The language code for this term.
+   * @param $expected_label
+   *   The label the migrated entity should have.
+   * @param $expected_vid
+   *   The parent vocabulary the migrated entity should have.
+   * @param string|null $expected_description
+   *   The description the migrated entity should have.
+   * @param string|null $expected_format
+   *   The format the migrated entity should have.
+   * @param int $expected_weight
+   *   The weight the migrated entity should have.
+   * @param array $expected_parents
+   *   The parent terms the migrated entity should have.
+   * @param int|null $expected_container_flag
+   *   The term should be a container entity.
+   *
+   * @internal
+   */
+  protected function assertEntity(int $id, string $expected_language, string $expected_label, string $expected_vid, ?string $expected_description = '', ?string $expected_format = NULL, int $expected_weight = 0, array $expected_parents = [], int|null $expected_container_flag = NULL): void {
+    /** @var \Drupal\taxonomy\TermInterface $entity */
+    $entity = Term::load($id);
+    $this->assertInstanceOf(TermInterface::class, $entity);
+    $this->assertSame($expected_language, $entity->language()->getId());
+    $this->assertEquals($expected_label, $entity->label());
+    $this->assertEquals($expected_vid, $entity->bundle());
+    $this->assertEquals($expected_description, $entity->getDescription());
+    $this->assertEquals($expected_format, $entity->getFormat());
+    $this->assertEquals($expected_weight, $entity->getWeight());
+    $this->assertEquals($expected_parents, array_column($entity->get('parent')
+      ->getValue(), 'target_id'));
+    $this->assertHierarchy($expected_vid, $id, $expected_parents);
+    if (isset($expected_container_flag)) {
+      $this->assertEquals($expected_container_flag, $entity->forum_container->value);
+    }
+  }
+
+  /**
+   * Retrieves the parent term IDs for a given term.
+   *
+   * @param $tid
+   *   ID of the term to check.
+   *
+   * @return array
+   *   List of parent term IDs.
+   */
+  protected function getParentIDs($tid) {
+    return array_keys(\Drupal::entityTypeManager()
+      ->getStorage('taxonomy_term')
+      ->loadParents($tid));
+  }
+
+  /**
+   * Assert that a term is present in the tree storage, with the right parents.
+   *
+   * @param string $vid
+   *   Vocabulary ID.
+   * @param int $tid
+   *   ID of the term to check.
+   * @param array $parent_ids
+   *   The expected parent term IDs.
+   */
+  protected function assertHierarchy(string $vid, int $tid, array $parent_ids): void {
+    if (!isset($this->treeData[$vid])) {
+      $tree = \Drupal::entityTypeManager()
+        ->getStorage('taxonomy_term')
+        ->loadTree($vid);
+      $this->treeData[$vid] = [];
+      foreach ($tree as $item) {
+        $this->treeData[$vid][$item->tid] = $item;
+      }
+    }
+
+    $this->assertArrayHasKey($tid, $this->treeData[$vid], "Term $tid exists in taxonomy tree");
+    $term = $this->treeData[$vid][$tid];
+    $this->assertEquals($parent_ids, $term->parents, "Term $tid has correct parents in taxonomy tree");
+  }
+
+}

core/modules/forum/tests/src/Kernel/Migrate/d6/MigrateBlockTest.php

@@ -0,0 +1,132 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Kernel\Migrate\d6;
+
+use Drupal\block\Entity\Block;
+use Drupal\Tests\migrate_drupal\Kernel\d6\MigrateDrupal6TestBase;
+
+/**
+ * Tests migration of forum blocks.
+ *
+ * @group forum
+ */
+class MigrateBlockTest extends MigrateDrupal6TestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'block',
+    'block_content',
+    'comment',
+    'forum',
+    'node',
+    'path_alias',
+    'taxonomy',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->installEntitySchema('path_alias');
+
+    // Install the themes used for this test.
+    $this->installEntitySchema('block_content');
+    $this->container->get('theme_installer')->install(['olivero', 'test_theme']);
+
+    $this->installConfig(['block_content']);
+
+    // Set Olivero as the default public theme.
+    $config = $this->config('system.theme');
+    $config->set('default', 'olivero');
+    $config->save();
+
+    $this->executeMigrations([
+      'd6_filter_format',
+      'block_content_type',
+      'block_content_body_field',
+      'd6_custom_block',
+      'd6_user_role',
+      'd6_block',
+    ]);
+    block_rebuild();
+  }
+
+  /**
+   * Gets the path to the fixture file.
+   */
+  protected function getFixtureFilePath() {
+    return __DIR__ . '/../../../../fixtures/drupal6.php';
+  }
+
+  /**
+   * Asserts various aspects of a block.
+   *
+   * @param string $id
+   *   The block ID.
+   * @param array $visibility
+   *   The block visibility settings.
+   * @param string $region
+   *   The display region.
+   * @param string $theme
+   *   The theme.
+   * @param int $weight
+   *   The block weight.
+   * @param array $settings
+   *   (optional) The block settings.
+   * @param bool $status
+   *   Whether the block is expected to be enabled or disabled.
+   *
+   * @internal
+   */
+  public function assertEntity(string $id, array $visibility, string $region, string $theme, int $weight, array $settings = [], bool $status = TRUE): void {
+    $block = Block::load($id);
+    $this->assertInstanceOf(Block::class, $block);
+    $this->assertSame($visibility, $block->getVisibility());
+    $this->assertSame($region, $block->getRegion());
+    $this->assertSame($theme, $block->getTheme());
+    $this->assertSame($weight, $block->getWeight());
+    $this->assertSame($status, $block->status());
+    if ($settings) {
+      $block_settings = $block->get('settings');
+      $block_settings['id'] = current(explode(':', $block_settings['id']));
+      $this->assertEquals($settings, $block_settings);
+    }
+  }
+
+  /**
+   * Tests the block migration.
+   */
+  public function testBlockMigration(): void {
+
+    // Check forum block settings.
+    $settings = [
+      'id' => 'forum_active_block',
+      'label' => '',
+      'provider' => 'forum',
+      'label_display' => '0',
+      'block_count' => 3,
+      'properties' => [
+        'administrative' => '1',
+      ],
+    ];
+    $this->assertEntity('forum', [], 'sidebar', 'olivero', -8, $settings);
+
+    $settings = [
+      'id' => 'forum_new_block',
+      'label' => '',
+      'provider' => 'forum',
+      'label_display' => '0',
+      'block_count' => 4,
+      'properties' => [
+        'administrative' => '1',
+      ],
+    ];
+    $this->assertEntity('forum_1', [], 'sidebar', 'olivero', -9, $settings);
+  }
+
+}

core/modules/forum/tests/src/Kernel/Migrate/d6/MigrateForumConfigsTest.php

@@ -0,0 +1,57 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Kernel\Migrate\d6;
+
+use Drupal\Tests\SchemaCheckTestTrait;
+use Drupal\Tests\migrate_drupal\Kernel\d6\MigrateDrupal6TestBase;
+
+/**
+ * Upgrade variables to forum.settings.yml.
+ *
+ * @group migrate_drupal_6
+ * @group legacy
+ */
+class MigrateForumConfigsTest extends MigrateDrupal6TestBase {
+
+  use SchemaCheckTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['comment', 'forum', 'taxonomy'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->executeMigration('d6_taxonomy_vocabulary');
+    $this->executeMigration('d6_forum_settings');
+  }
+
+  /**
+   * Gets the path to the fixture file.
+   */
+  protected function getFixtureFilePath() {
+    return __DIR__ . '/../../../../fixtures/drupal6.php';
+  }
+
+  /**
+   * Tests migration of forum variables to forum.settings.yml.
+   */
+  public function testForumSettings(): void {
+    $config = $this->config('forum.settings');
+    $this->assertSame(15, $config->get('topics.hot_threshold'));
+    $this->assertSame(25, $config->get('topics.page_limit'));
+    $this->assertSame(1, $config->get('topics.order'));
+    $this->assertSame('forums', $config->get('vocabulary'));
+    // This is 'forum_block_num_0' in D6, but block:active:limit' in D8.
+    $this->assertSame(3, $config->get('block.active.limit'));
+    // This is 'forum_block_num_1' in D6, but 'block:new:limit' in D8.
+    $this->assertSame(4, $config->get('block.new.limit'));
+    $this->assertConfigSchema(\Drupal::service('config.typed'), 'forum.settings', $config->get());
+  }
+
+}

core/modules/forum/tests/src/Kernel/Migrate/d6/MigrateForumTest.php

@@ -0,0 +1,87 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Kernel\Migrate\d6;
+
+use Drupal\Core\Entity\Entity\EntityFormDisplay;
+use Drupal\Core\Entity\Entity\EntityViewDisplay;
+use Drupal\field\Entity\FieldConfig;
+use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\node\Entity\Node;
+use Drupal\Tests\node\Kernel\Migrate\d6\MigrateNodeTestBase;
+
+/**
+ * Tests forum migration from Drupal 6 to Drupal 8.
+ *
+ * @group migrate_drupal_6
+ * @group legacy
+ */
+class MigrateForumTest extends MigrateNodeTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'comment',
+    'forum',
+    'menu_ui',
+    'taxonomy',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->installEntitySchema('comment');
+    $this->installSchema('comment', ['comment_entity_statistics']);
+    $this->installSchema('forum', ['forum', 'forum_index']);
+    $this->installConfig(['comment', 'forum']);
+    $this->migrateContent();
+    $this->migrateTaxonomy();
+    $this->executeMigrations([
+      'd6_comment_type',
+      'd6_comment_field',
+      'd6_comment_field_instance',
+      'd6_comment_entity_display',
+      'd6_comment_entity_form_display',
+      'd6_comment',
+      'd6_term_node',
+    ]);
+  }
+
+  /**
+   * Gets the path to the fixture file.
+   */
+  protected function getFixtureFilePath() {
+    return __DIR__ . '/../../../../fixtures/drupal6.php';
+  }
+
+  /**
+   * Tests forum migration.
+   */
+  public function testForumMigration(): void {
+    // Tests that the taxonomy_forums field storage config exists.
+    $field_storage_config = FieldStorageConfig::load('node.taxonomy_forums');
+    $this->assertInstanceOf(FieldStorageConfig::class, $field_storage_config);
+
+    // Tests that the taxonomy_forums field config exists.
+    $field_config = FieldConfig::load('node.forum.taxonomy_forums');
+    $this->assertInstanceOf(FieldConfig::class, $field_config);
+
+    // Tests that the taxonomy_forums entity view display component exists.
+    $entity_view_display = EntityViewDisplay::load('node.forum.default')->getComponent('taxonomy_forums');
+    $this->assertIsArray($entity_view_display);
+
+    // Tests that the taxonomy_forums entity form display component exists.
+    $entity_form_display = EntityFormDisplay::load('node.forum.default')->getComponent('taxonomy_forums');
+    $this->assertIsArray($entity_form_display);
+
+    // Test that the taxonomy_forums field has the right value.
+    $node = Node::load(19);
+    $this->assertEquals(8, $node->taxonomy_forums->target_id);
+  }
+
+}

core/modules/forum/tests/src/Kernel/Migrate/d6/MigrateTaxonomyTermTest.php

@@ -0,0 +1,52 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Kernel\Migrate\d6;
+
+use Drupal\Tests\forum\Kernel\Migrate\MigrateTestTrait;
+use Drupal\Tests\migrate_drupal\Kernel\d6\MigrateDrupal6TestBase;
+
+/**
+ * Test migration of forum taxonomy terms.
+ *
+ * @group forum
+ */
+class MigrateTaxonomyTermTest extends MigrateDrupal6TestBase {
+
+  use MigrateTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['taxonomy', 'comment', 'forum', 'menu_ui'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->installEntitySchema('taxonomy_term');
+    $this->installConfig('forum');
+    $this->executeMigrations(['d6_taxonomy_vocabulary', 'd6_taxonomy_term']);
+  }
+
+  /**
+   * Gets the path to the fixture file.
+   */
+  protected function getFixtureFilePath() {
+    return __DIR__ . '/../../../../fixtures/drupal6.php';
+  }
+
+  /**
+   * Assert the forum taxonomy terms.
+   */
+  public function testTaxonomyTerms(): void {
+    $this->assertEntity(8, 'en', 'General discussion', 'forums', '', NULL, 2, ['0'], 0);
+    $this->assertEntity(9, 'en', 'Earth', 'forums', '', NULL, 0, ['0'], 1);
+    $this->assertEntity(10, 'en', 'Birds', 'forums', '', NULL, 0, ['9'], 0);
+    $this->assertEntity(11, 'en', 'Oak', 'trees', '', NULL, 0, ['0'], NULL);
+    $this->assertEntity(12, 'en', 'Ash', 'trees', '', NULL, 0, ['0'], NULL);
+  }
+
+}

core/modules/forum/tests/src/Kernel/Migrate/d6/MigrateTaxonomyVocabularyTest.php

@@ -0,0 +1,65 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Kernel\Migrate\d6;
+
+use Drupal\Tests\taxonomy\Kernel\Migrate\d6\MigrateTaxonomyVocabularyTest as TaxonomyVocabularyTest;
+use Drupal\taxonomy\Entity\Vocabulary;
+use Drupal\taxonomy\VocabularyInterface;
+
+/**
+ * Migrate forum vocabulary to taxonomy.vocabulary.*.yml.
+ *
+ * @group forum
+ */
+class MigrateTaxonomyVocabularyTest extends TaxonomyVocabularyTest {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'comment',
+    'forum',
+  ];
+
+  /**
+   * Gets the path to the fixture file.
+   */
+  protected function getFixtureFilePath() {
+    return __DIR__ . '/../../../../fixtures/drupal6.php';
+  }
+
+  /**
+   * Validate a migrated vocabulary contains the expected values.
+   *
+   * @param string $id
+   *   Entity ID to load and check.
+   * @param $expected_label
+   *   The label the migrated entity should have.
+   * @param $expected_description
+   *   The description the migrated entity should have.
+   * @param $expected_weight
+   *   The weight the migrated entity should have.
+   *
+   * @internal
+   */
+  protected function assertEntity(string $id, string $expected_label, string $expected_description, int $expected_weight): void {
+    /** @var \Drupal\taxonomy\VocabularyInterface $entity */
+    $entity = Vocabulary::load($id);
+    $this->assertInstanceOf(VocabularyInterface::class, $entity);
+    $this->assertSame($expected_label, $entity->label());
+    $this->assertSame($expected_description, $entity->getDescription());
+    $this->assertSame($expected_weight, (int) $entity->get('weight'));
+  }
+
+  /**
+   * Tests the Drupal 6 taxonomy vocabularies migration.
+   */
+  public function testTaxonomyVocabulary(): void {
+    $this->assertEntity('forums', 'Forums', '', 0);
+    $this->assertEntity('trees', 'Trees', 'A list of trees.', 0);
+    $this->assertEntity('freetags', 'FreeTags', '', 0);
+  }
+
+}

core/modules/forum/tests/src/Kernel/Migrate/d6/MigrateVocabularyEntityDisplayTest.php

@@ -0,0 +1,116 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Kernel\Migrate\d6;
+
+use Drupal\Core\Entity\Display\EntityViewDisplayInterface;
+use Drupal\Core\Entity\Entity\EntityViewDisplay;
+use Drupal\Tests\migrate_drupal\Kernel\d6\MigrateDrupal6TestBase;
+
+/**
+ * Vocabulary entity display migration.
+ *
+ * @group forum
+ */
+class MigrateVocabularyEntityDisplayTest extends MigrateDrupal6TestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'field',
+    'comment',
+    'forum',
+    'taxonomy',
+    'menu_ui',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // Execute Dependency Migrations.
+    $this->migrateContentTypes();
+    $this->installEntitySchema('taxonomy_term');
+    $this->executeMigrations([
+      'd6_node_type',
+      'd6_taxonomy_vocabulary',
+      'd6_vocabulary_field',
+      'd6_vocabulary_field_instance',
+      'd6_vocabulary_entity_display',
+    ]);
+  }
+
+  /**
+   * Gets the path to the fixture file.
+   */
+  protected function getFixtureFilePath() {
+    return __DIR__ . '/../../../../fixtures/drupal6.php';
+  }
+
+  /**
+   * Tests the Drupal 6 vocabulary-node type association to Drupal 8 migration.
+   */
+  public function testVocabularyEntityDisplay(): void {
+    $this->assertEntity('node.forum.default');
+    $this->assertComponent('node.forum.default', 'taxonomy_forums', 'entity_reference_label', 'hidden', 20);
+    $this->assertComponent('node.forum.default', 'field_trees', 'entity_reference_label', 'hidden', 20);
+    $this->assertComponent('node.forum.default', 'field_freetags', 'entity_reference_label', 'hidden', 20);
+  }
+
+  /**
+   * Asserts various aspects of a view display.
+   *
+   * @param string $id
+   *   The view display ID.
+   *
+   * @internal
+   */
+  protected function assertEntity(string $id): void {
+    $display = EntityViewDisplay::load($id);
+    $this->assertInstanceOf(EntityViewDisplayInterface::class, $display);
+  }
+
+  /**
+   * Asserts various aspects of a particular component of a view display.
+   *
+   * @param string $display_id
+   *   The view display ID.
+   * @param string $component_id
+   *   The component ID.
+   * @param string $type
+   *   The expected component type (formatter plugin ID).
+   * @param string $label
+   *   The expected label of the component.
+   * @param int $weight
+   *   The expected weight of the component.
+   *
+   * @internal
+   */
+  protected function assertComponent(string $display_id, string $component_id, string $type, string $label, int $weight): void {
+    $component = EntityViewDisplay::load($display_id)->getComponent($component_id);
+    $this->assertIsArray($component);
+    $this->assertSame($type, $component['type']);
+    $this->assertSame($label, $component['label']);
+    $this->assertSame($weight, $component['weight']);
+  }
+
+  /**
+   * Asserts that a particular component is NOT included in a display.
+   *
+   * @param string $display_id
+   *   The display ID.
+   * @param string $component_id
+   *   The component ID.
+   *
+   * @internal
+   */
+  protected function assertComponentNotExists(string $display_id, string $component_id): void {
+    $component = EntityViewDisplay::load($display_id)->getComponent($component_id);
+    $this->assertNull($component);
+  }
+
+}

core/modules/forum/tests/src/Kernel/Migrate/d6/MigrateVocabularyEntityFormDisplayTest.php

@@ -0,0 +1,99 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Kernel\Migrate\d6;
+
+use Drupal\Core\Entity\Display\EntityFormDisplayInterface;
+use Drupal\Core\Entity\Entity\EntityFormDisplay;
+use Drupal\Tests\migrate_drupal\Kernel\d6\MigrateDrupal6TestBase;
+
+/**
+ * Vocabulary entity form display migration.
+ *
+ * @group forum
+ */
+class MigrateVocabularyEntityFormDisplayTest extends MigrateDrupal6TestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['comment', 'forum', 'taxonomy', 'menu_ui'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // Execute Dependency Migrations.
+    $this->migrateContentTypes();
+    $this->installEntitySchema('taxonomy_term');
+    $this->executeMigrations([
+      'd6_taxonomy_vocabulary',
+      'd6_vocabulary_field',
+      'd6_vocabulary_field_instance',
+      'd6_vocabulary_entity_display',
+      'd6_vocabulary_entity_form_display',
+    ]);
+  }
+
+  /**
+   * Gets the path to the fixture file.
+   */
+  protected function getFixtureFilePath() {
+    return __DIR__ . '/../../../../fixtures/drupal6.php';
+  }
+
+  /**
+   * Tests the Drupal 6 vocabulary-node type association to Drupal 8 migration.
+   */
+  public function testVocabularyEntityFormDisplay(): void {
+    $this->assertEntity('node.forum.default', 'node', 'forum');
+    $this->assertComponent('node.forum.default', 'taxonomy_forums', 'options_select', 20);
+    $this->assertComponent('node.forum.default', 'field_trees', 'options_select', 20);
+    $this->assertComponent('node.forum.default', 'field_freetags', 'entity_reference_autocomplete_tags', 20);
+  }
+
+  /**
+   * Asserts various aspects of a form display entity.
+   *
+   * @param string $id
+   *   The entity ID.
+   * @param string $expected_entity_type
+   *   The expected entity type to which the display settings are attached.
+   * @param string $expected_bundle
+   *   The expected bundle to which the display settings are attached.
+   *
+   * @internal
+   */
+  protected function assertEntity(string $id, string $expected_entity_type, string $expected_bundle): void {
+    /** @var \Drupal\Core\Entity\Display\EntityFormDisplayInterface $entity */
+    $entity = EntityFormDisplay::load($id);
+    $this->assertInstanceOf(EntityFormDisplayInterface::class, $entity);
+    $this->assertSame($expected_entity_type, $entity->getTargetEntityTypeId());
+    $this->assertSame($expected_bundle, $entity->getTargetBundle());
+  }
+
+  /**
+   * Asserts various aspects of a particular component of a form display.
+   *
+   * @param string $display_id
+   *   The form display ID.
+   * @param string $component_id
+   *   The component ID.
+   * @param string $widget_type
+   *   The expected widget type.
+   * @param int $weight
+   *   The expected weight of the component.
+   *
+   * @internal
+   */
+  protected function assertComponent(string $display_id, string $component_id, string $widget_type, int $weight): void {
+    $component = EntityFormDisplay::load($display_id)->getComponent($component_id);
+    $this->assertIsArray($component);
+    $this->assertSame($widget_type, $component['type']);
+    $this->assertSame($weight, $component['weight']);
+  }
+
+}

core/modules/forum/tests/src/Kernel/Migrate/d6/MigrateVocabularyFieldInstanceTest.php

@@ -0,0 +1,126 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Kernel\Migrate\d6;
+
+use Drupal\Tests\migrate_drupal\Kernel\d6\MigrateDrupal6TestBase;
+use Drupal\field\Entity\FieldConfig;
+use Drupal\field\FieldConfigInterface;
+
+/**
+ * Vocabulary field instance migration.
+ *
+ * @group forum
+ */
+class MigrateVocabularyFieldInstanceTest extends MigrateDrupal6TestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'comment',
+    'forum',
+    'menu_ui',
+    'taxonomy',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    // Execute Dependency Migrations.
+    $this->migrateContentTypes();
+    $this->installEntitySchema('taxonomy_term');
+    $this->executeMigrations([
+      'd6_node_type',
+      'd6_taxonomy_vocabulary',
+      'd6_vocabulary_field',
+      'd6_vocabulary_field_instance',
+    ]);
+  }
+
+  /**
+   * Gets the path to the fixture file.
+   */
+  protected function getFixtureFilePath() {
+    return __DIR__ . '/../../../../fixtures/drupal6.php';
+  }
+
+  /**
+   * Tests the Drupal 6 vocabulary-node type association migration.
+   */
+  public function testVocabularyFieldInstance(): void {
+    $this->assertEntity('node.forum.taxonomy_forums', 'Forums', 'entity_reference', FALSE, FALSE);
+    $this->assertEntity('node.forum.field_trees', 'Trees', 'entity_reference', FALSE, FALSE);
+    $this->assertEntity('node.forum.field_freetags', 'FreeTags', 'entity_reference', FALSE, FALSE);
+  }
+
+  /**
+   * Asserts various aspects of a field config entity.
+   *
+   * @param string $id
+   *   The entity ID in the form ENTITY_TYPE.BUNDLE.FIELD_NAME.
+   * @param string $expected_label
+   *   The expected field label.
+   * @param string $expected_field_type
+   *   The expected field type.
+   * @param bool $is_required
+   *   Whether or not the field is required.
+   * @param bool $expected_translatable
+   *   Whether or not the field is expected to be translatable.
+   *
+   * @internal
+   */
+  protected function assertEntity(string $id, string $expected_label, string $expected_field_type, bool $is_required, bool $expected_translatable): void {
+    [$expected_entity_type, $expected_bundle, $expected_name] = explode('.', $id);
+
+    /** @var \Drupal\field\FieldConfigInterface $field */
+    $field = FieldConfig::load($id);
+    $this->assertInstanceOf(FieldConfigInterface::class, $field);
+    $this->assertEquals($expected_label, $field->label());
+    $this->assertEquals($expected_field_type, $field->getType());
+    $this->assertEquals($expected_entity_type, $field->getTargetEntityTypeId());
+    $this->assertEquals($expected_bundle, $field->getTargetBundle());
+    $this->assertEquals($expected_name, $field->getName());
+    $this->assertEquals($is_required, $field->isRequired());
+    $this->assertEquals($expected_entity_type . '.' . $expected_name, $field->getFieldStorageDefinition()->id());
+    $this->assertEquals($expected_translatable, $field->isTranslatable());
+  }
+
+  /**
+   * Asserts the settings of a link field config entity.
+   *
+   * @param string $id
+   *   The entity ID in the form ENTITY_TYPE.BUNDLE.FIELD_NAME.
+   * @param int $title_setting
+   *   The expected title setting.
+   *
+   * @internal
+   */
+  protected function assertLinkFields(string $id, int $title_setting): void {
+    $field = FieldConfig::load($id);
+    $this->assertSame($title_setting, $field->getSetting('title'));
+  }
+
+  /**
+   * Asserts the settings of an entity reference field config entity.
+   *
+   * @param string $id
+   *   The entity ID in the form ENTITY_TYPE.BUNDLE.FIELD_NAME.
+   * @param string[] $target_bundles
+   *   An array of expected target bundles.
+   *
+   * @internal
+   */
+  protected function assertEntityReferenceFields(string $id, array $target_bundles): void {
+    $field = FieldConfig::load($id);
+    $handler_settings = $field->getSetting('handler_settings');
+    $this->assertArrayHasKey('target_bundles', $handler_settings);
+    foreach ($handler_settings['target_bundles'] as $target_bundle) {
+      $this->assertContains($target_bundle, $target_bundles);
+    }
+  }
+
+}

core/modules/forum/tests/src/Kernel/Migrate/d6/MigrateVocabularyFieldTest.php

@@ -0,0 +1,87 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Kernel\Migrate\d6;
+
+use Drupal\Tests\migrate_drupal\Kernel\d6\MigrateDrupal6TestBase;
+use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\field\FieldStorageConfigInterface;
+
+/**
+ * Vocabulary field migration.
+ *
+ * @group forum
+ */
+class MigrateVocabularyFieldTest extends MigrateDrupal6TestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'comment',
+    'forum',
+    'taxonomy',
+    'menu_ui',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->migrateTaxonomy();
+  }
+
+  /**
+   * Gets the path to the fixture file.
+   */
+  protected function getFixtureFilePath() {
+    return __DIR__ . '/../../../../fixtures/drupal6.php';
+  }
+
+  /**
+   * Tests the Drupal 6 vocabulary-node type association migration.
+   */
+  public function testVocabularyField(): void {
+    // Test that the field exists.
+    $this->assertEntity('node.field_freetags', 'entity_reference', TRUE, -1);
+    $this->assertEntity('node.field_trees', 'entity_reference', TRUE, 1);
+    $this->assertEntity('node.taxonomy_forums', 'entity_reference', TRUE, 1);
+  }
+
+  /**
+   * Asserts various aspects of a field_storage_config entity.
+   *
+   * @param string $id
+   *   The entity ID in the form ENTITY_TYPE.FIELD_NAME.
+   * @param string $expected_type
+   *   The expected field type.
+   * @param bool $expected_translatable
+   *   Whether or not the field is expected to be translatable.
+   * @param int $expected_cardinality
+   *   The expected cardinality of the field.
+   *
+   * @internal
+   */
+  protected function assertEntity(string $id, string $expected_type, bool $expected_translatable, int $expected_cardinality): void {
+    [$expected_entity_type, $expected_name] = explode('.', $id);
+
+    /** @var \Drupal\field\FieldStorageConfigInterface $field */
+    $field = FieldStorageConfig::load($id);
+    $this->assertInstanceOf(FieldStorageConfigInterface::class, $field);
+    $this->assertEquals($expected_name, $field->getName());
+    $this->assertEquals($expected_type, $field->getType());
+    $this->assertEquals($expected_translatable, $field->isTranslatable());
+    $this->assertEquals($expected_entity_type, $field->getTargetEntityTypeId());
+
+    if ($expected_cardinality === 1) {
+      $this->assertFalse($field->isMultiple());
+    }
+    else {
+      $this->assertTrue($field->isMultiple());
+    }
+    $this->assertEquals($expected_cardinality, $field->getCardinality());
+  }
+
+}

core/modules/forum/tests/src/Kernel/Migrate/d7/MigrateForumSettingsTest.php

@@ -0,0 +1,63 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Kernel\Migrate\d7;
+
+use Drupal\Tests\migrate_drupal\Kernel\d7\MigrateDrupal7TestBase;
+
+/**
+ * Tests migration of Forum's variables to configuration.
+ *
+ * @group forum
+ * @group legacy
+ */
+class MigrateForumSettingsTest extends MigrateDrupal7TestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * Don't alphabetize these. They're in dependency order.
+   *
+   * @var array
+   */
+  protected static $modules = [
+    'comment',
+    'field',
+    'filter',
+    'text',
+    'node',
+    'taxonomy',
+    'forum',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->executeMigration('d7_taxonomy_vocabulary');
+    $this->executeMigration('d7_forum_settings');
+  }
+
+  /**
+   * Gets the path to the fixture file.
+   */
+  protected function getFixtureFilePath() {
+    return __DIR__ . '/../../../../fixtures/drupal7.php';
+  }
+
+  /**
+   * Tests the migration of Forum's settings to configuration.
+   */
+  public function testForumSettingsMigration(): void {
+    $config = $this->config('forum.settings');
+    $this->assertSame(9, $config->get('block.active.limit'));
+    $this->assertSame(4, $config->get('block.new.limit'));
+    $this->assertSame(10, $config->get('topics.hot_threshold'));
+    $this->assertSame(25, $config->get('topics.page_limit'));
+    $this->assertSame(1, $config->get('topics.order'));
+    $this->assertSame('forums', $config->get('vocabulary'));
+  }
+
+}

core/modules/forum/tests/src/Kernel/Migrate/d7/MigrateLanguageContentTaxonomyVocabularySettingsTest.php

@@ -0,0 +1,32 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Kernel\Migrate\d7;
+
+use Drupal\Core\Language\LanguageInterface;
+use Drupal\Tests\language\Kernel\Migrate\d7\MigrateLanguageContentTaxonomyVocabularySettingsTest as CoreTest;
+
+/**
+ * Tests migration of i18ntaxonomy vocabulary settings.
+ *
+ * @group forum
+ */
+class MigrateLanguageContentTaxonomyVocabularySettingsTest extends CoreTest {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'comment',
+    'forum',
+  ];
+
+  /**
+   * Tests migration of 18ntaxonomy vocabulary settings.
+   */
+  public function testLanguageContentTaxonomy(): void {
+    $this->assertLanguageContentSettings('taxonomy_term', 'forums', LanguageInterface::LANGCODE_NOT_SPECIFIED, FALSE, ['enabled' => FALSE]);
+  }
+
+}

core/modules/forum/tests/src/Kernel/Migrate/d7/MigrateTaxonomyTermTest.php

@@ -0,0 +1,86 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Kernel\Migrate\d7;
+
+use Drupal\Tests\forum\Kernel\Migrate\MigrateTestTrait;
+use Drupal\Tests\migrate_drupal\Kernel\d7\MigrateDrupal7TestBase;
+use Drupal\taxonomy\Entity\Term;
+
+/**
+ * Test migration of forum taxonomy terms.
+ *
+ * @group forum
+ */
+class MigrateTaxonomyTermTest extends MigrateDrupal7TestBase {
+
+  use MigrateTestTrait;
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'comment',
+    'forum',
+    'content_translation',
+    'datetime',
+    'datetime_range',
+    'image',
+    'language',
+    'menu_ui',
+    'node',
+    'taxonomy',
+    'text',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->installConfig('forum');
+    $this->installEntitySchema('comment');
+    $this->installEntitySchema('file');
+
+    $this->migrateTaxonomyTerms();
+    $this->executeMigrations([
+      'language',
+      'd7_user_role',
+      'd7_user',
+      'd7_entity_translation_settings',
+      'd7_taxonomy_term_entity_translation',
+    ]);
+  }
+
+  /**
+   * Gets the path to the fixture file.
+   */
+  protected function getFixtureFilePath() {
+    return __DIR__ . '/../../../../fixtures/drupal7.php';
+  }
+
+  /**
+   * Assert the forum taxonomy terms.
+   */
+  public function testTaxonomyTerms(): void {
+    $this->assertEntity(1, 'en', 'General discussion', 'forums', '', NULL, 2, ['0'], 0);
+
+    $this->assertEntity(5, 'en', 'Custom Forum', 'forums', 'Where the cool kids are.', NULL, 3, ['0'], 0);
+    $this->assertEntity(6, 'en', 'Games', 'forums', NULL, '', 4, ['0'], 1);
+    $this->assertEntity(7, 'en', 'Minecraft', 'forums', '', NULL, 1, [6], 0);
+    $this->assertEntity(8, 'en', 'Half Life 3', 'forums', '', NULL, 0, [6], 0);
+
+    // Verify that we still can create forum containers after the migration.
+    $term = Term::create([
+      'vid' => 'forums',
+      'name' => 'Forum Container',
+      'forum_container' => 1,
+    ]);
+    $term->save();
+
+    // Reset the forums tree data so this new term is included in the tree.
+    unset($this->treeData['forums']);
+    $this->assertEntity(9, 'en', 'Forum Container', 'forums', '', '', 0, ['0'], 1);
+  }
+
+}

core/modules/forum/tests/src/Kernel/Migrate/d7/MigrateTaxonomyTermTranslationTest.php

@@ -0,0 +1,43 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Kernel\Migrate\d7;
+
+use Drupal\Tests\taxonomy\Kernel\Migrate\d7\MigrateTaxonomyTermTranslationTest as TaxonomyTermTranslationTest;
+
+/**
+ * Test migration of translated taxonomy terms.
+ *
+ * @group forum
+ */
+class MigrateTaxonomyTermTranslationTest extends TaxonomyTermTranslationTest {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'comment',
+    'forum',
+  ];
+
+  /**
+   * Gets the path to the fixture file.
+   */
+  protected function getFixtureFilePath() {
+    return __DIR__ . '/../../../../fixtures/drupal7.php';
+  }
+
+  /**
+   * Tests the Drupal i18n  taxonomy term to Drupal 8 migration.
+   */
+  public function testTaxonomyTermTranslation(): void {
+    // Forums vocabulary, no multilingual option.
+    $this->assertEntity(1, 'en', 'General discussion', 'forums', NULL, NULL, 2, []);
+    $this->assertEntity(5, 'en', 'Custom Forum', 'forums', 'Where the cool kids are.', NULL, 3, []);
+    $this->assertEntity(6, 'en', 'Games', 'forums', NULL, NULL, 4, []);
+    $this->assertEntity(7, 'en', 'Minecraft', 'forums', NULL, NULL, 1, ['6']);
+    $this->assertEntity(8, 'en', 'Half Life 3', 'forums', NULL, NULL, 0, ['6']);
+  }
+
+}

core/modules/forum/tests/src/Kernel/Migrate/d7/MigrateTaxonomyVocabularyTest.php

@@ -0,0 +1,39 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Kernel\Migrate\d7;
+
+use Drupal\Tests\taxonomy\Kernel\Migrate\d7\MigrateTaxonomyVocabularyTest as TaxonomyVocabularyTest;
+
+/**
+ * Migrate forum vocabulary to taxonomy.vocabulary.*.yml.
+ *
+ * @group forum
+ */
+class MigrateTaxonomyVocabularyTest extends TaxonomyVocabularyTest {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'comment',
+    'forum',
+  ];
+
+  /**
+   * Gets the path to the fixture file.
+   */
+  protected function getFixtureFilePath() {
+    return __DIR__ . '/../../../../fixtures/drupal7.php';
+  }
+
+  /**
+   * Tests the Drupal 7 taxonomy vocabularies to Drupal 8 migration.
+   */
+  public function testTaxonomyVocabulary(): void {
+    $this->assertEntity('tags', 'Tags', 'Use tags to group articles on similar topics into categories.', 0);
+    $this->assertEntity('forums', 'Subject of discussion', 'Forum navigation vocabulary', -10);
+  }
+
+}

core/modules/forum/tests/src/Unit/Breadcrumb/ForumBreadcrumbBuilderBaseTest.php

@@ -0,0 +1,149 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Unit\Breadcrumb;
+
+use Drupal\Core\Cache\Cache;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Link;
+use Drupal\Tests\UnitTestCase;
+use Symfony\Component\DependencyInjection\Container;
+
+/**
+ * @coversDefaultClass \Drupal\forum\Breadcrumb\ForumBreadcrumbBuilderBase
+ * @group forum
+ * @group legacy
+ */
+class ForumBreadcrumbBuilderBaseTest extends UnitTestCase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $cache_contexts_manager = $this->getMockBuilder('Drupal\Core\Cache\Context\CacheContextsManager')
+      ->disableOriginalConstructor()
+      ->getMock();
+    $cache_contexts_manager->method('assertValidTokens')->willReturn(TRUE);
+    $container = new Container();
+    $container->set('cache_contexts_manager', $cache_contexts_manager);
+    \Drupal::setContainer($container);
+  }
+
+  /**
+   * Tests ForumBreadcrumbBuilderBase::__construct().
+   *
+   * @covers ::__construct
+   */
+  public function testConstructor(): void {
+    // Make some test doubles.
+    $entity_type_manager = $this->createMock(EntityTypeManagerInterface::class);
+    $config_factory = $this->getConfigFactoryStub(
+      [
+        'forum.settings' => ['IAmATestKey' => 'IAmATestValue'],
+      ]
+    );
+    $forum_manager = $this->createMock('Drupal\forum\ForumManagerInterface');
+    $translation_manager = $this->createMock('Drupal\Core\StringTranslation\TranslationInterface');
+
+    // Make an object to test.
+    $builder = $this->getMockForAbstractClass(
+      'Drupal\forum\Breadcrumb\ForumBreadcrumbBuilderBase',
+      // Constructor array.
+      [
+        $entity_type_manager,
+        $config_factory,
+        $forum_manager,
+        $translation_manager,
+      ]
+    );
+
+    // Test that the constructor made a config object with our info in it.
+    $reflector = new \ReflectionClass($builder);
+    $ref_property = $reflector->getProperty('config');
+    $config = $ref_property->getValue($builder);
+    $this->assertEquals('IAmATestValue', $config->get('IAmATestKey'));
+  }
+
+  /**
+   * Tests ForumBreadcrumbBuilderBase::build().
+   *
+   * @see \Drupal\forum\Breadcrumb\ForumBreadcrumbBuilderBase::build()
+   *
+   * @covers ::build
+   */
+  public function testBuild(): void {
+    // Build all our dependencies, backwards.
+    $translation_manager = $this->getMockBuilder('Drupal\Core\StringTranslation\TranslationInterface')
+      ->disableOriginalConstructor()
+      ->getMock();
+
+    $forum_manager = $this->getMockBuilder('Drupal\forum\ForumManagerInterface')
+      ->disableOriginalConstructor()
+      ->getMock();
+
+    $prophecy = $this->prophesize('Drupal\taxonomy\VocabularyInterface');
+    $prophecy->label()->willReturn('Fora_is_the_plural_of_forum');
+    $prophecy->id()->willReturn(5);
+    $prophecy->getCacheTags()->willReturn(['taxonomy_vocabulary:5']);
+    $prophecy->getCacheContexts()->willReturn([]);
+    $prophecy->getCacheMaxAge()->willReturn(Cache::PERMANENT);
+
+    $vocab_storage = $this->createMock('Drupal\Core\Entity\EntityStorageInterface');
+    $vocab_storage->expects($this->any())
+      ->method('load')
+      ->willReturnMap([
+        ['forums', $prophecy->reveal()],
+      ]);
+
+    $entity_type_manager = $this->createMock(EntityTypeManagerInterface::class);
+    $entity_type_manager->expects($this->any())
+      ->method('getStorage')
+      ->willReturnMap([
+        ['taxonomy_vocabulary', $vocab_storage],
+      ]);
+
+    $config_factory = $this->getConfigFactoryStub(
+      [
+        'forum.settings' => [
+          'vocabulary' => 'forums',
+        ],
+      ]
+    );
+
+    // Build a breadcrumb builder to test.
+    $breadcrumb_builder = $this->getMockForAbstractClass(
+      'Drupal\forum\Breadcrumb\ForumBreadcrumbBuilderBase',
+      // Constructor array.
+      [
+        $entity_type_manager,
+        $config_factory,
+        $forum_manager,
+        $translation_manager,
+      ]
+    );
+
+    // Add a translation manager for t().
+    $translation_manager = $this->getStringTranslationStub();
+    $breadcrumb_builder->setStringTranslation($translation_manager);
+
+    // Our empty data set.
+    $route_match = $this->createMock('Drupal\Core\Routing\RouteMatchInterface');
+
+    // Expected result set.
+    $expected = [
+      Link::createFromRoute('Home', '<front>'),
+      Link::createFromRoute('Fora_is_the_plural_of_forum', 'forum.index'),
+    ];
+
+    // And finally, the test.
+    $breadcrumb = $breadcrumb_builder->build($route_match);
+    $this->assertEquals($expected, $breadcrumb->getLinks());
+    $this->assertEquals(['route'], $breadcrumb->getCacheContexts());
+    $this->assertEquals(['taxonomy_vocabulary:5'], $breadcrumb->getCacheTags());
+    $this->assertEquals(Cache::PERMANENT, $breadcrumb->getCacheMaxAge());
+  }
+
+}

core/modules/forum/tests/src/Unit/Breadcrumb/ForumListingBreadcrumbBuilderTest.php

@@ -0,0 +1,218 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Unit\Breadcrumb;
+
+use Drupal\Core\Cache\Cache;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Link;
+use Drupal\forum\Breadcrumb\ForumListingBreadcrumbBuilder;
+use Drupal\taxonomy\Entity\Term;
+use Drupal\taxonomy\TermStorageInterface;
+use Drupal\Tests\UnitTestCase;
+use Symfony\Component\DependencyInjection\Container;
+
+/**
+ * @coversDefaultClass \Drupal\forum\Breadcrumb\ForumListingBreadcrumbBuilder
+ * @group forum
+ * @group legacy
+ */
+class ForumListingBreadcrumbBuilderTest extends UnitTestCase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $cache_contexts_manager = $this->getMockBuilder('Drupal\Core\Cache\Context\CacheContextsManager')
+      ->disableOriginalConstructor()
+      ->getMock();
+    $cache_contexts_manager->method('assertValidTokens')->willReturn(TRUE);
+    $container = new Container();
+    $container->set('cache_contexts_manager', $cache_contexts_manager);
+    \Drupal::setContainer($container);
+  }
+
+  /**
+   * Tests ForumListingBreadcrumbBuilder::applies().
+   *
+   * @param bool $expected
+   *   ForumListingBreadcrumbBuilder::applies() expected result.
+   * @param string|null $route_name
+   *   (optional) A route name.
+   * @param array $parameter_map
+   *   (optional) An array of parameter names and values.
+   *
+   * @dataProvider providerTestApplies
+   * @covers ::applies
+   */
+  public function testApplies(bool $expected, ?string $route_name = NULL, array $parameter_map = []): void {
+    // Make some test doubles.
+    $entity_type_manager = $this->createMock(EntityTypeManagerInterface::class);
+    $config_factory = $this->getConfigFactoryStub([]);
+    $forum_manager = $this->createMock('Drupal\forum\ForumManagerInterface');
+    $translation_manager = $this->createMock('Drupal\Core\StringTranslation\TranslationInterface');
+    $map = [];
+    if ($parameter_map) {
+      foreach ($parameter_map as $parameter) {
+        $map[] = [
+          $parameter[0],
+          $parameter[1] === TRUE ? $this->getMockBuilder(Term::class)->disableOriginalConstructor()->getMock() : $parameter[1],
+        ];
+      }
+    }
+
+    // Make an object to test.
+    $builder = new ForumListingBreadcrumbBuilder($entity_type_manager, $config_factory, $forum_manager, $translation_manager);
+
+    $route_match = $this->createMock('Drupal\Core\Routing\RouteMatchInterface');
+    $route_match->expects($this->once())
+      ->method('getRouteName')
+      ->willReturn($route_name);
+    $route_match->expects($this->any())
+      ->method('getParameter')
+      ->willReturnMap($map);
+
+    $this->assertEquals($expected, $builder->applies($route_match));
+  }
+
+  /**
+   * Provides test data for testApplies().
+   *
+   * @return \Generator
+   *   Datasets for testApplies(). Structured as such:
+   *   - ForumListBreadcrumbBuilder::applies() expected result.
+   *   - ForumListBreadcrumbBuilder::applies() $attributes input array.
+   */
+  public static function providerTestApplies(): \Generator {
+    yield [FALSE];
+    yield [FALSE, 'NOT.forum.page'];
+    yield [FALSE, 'forum.page'];
+    yield [TRUE, 'forum.page', [['taxonomy_term', 'anything']]];
+    yield [TRUE, 'forum.page', [['taxonomy_term', TRUE]]];
+  }
+
+  /**
+   * Tests ForumListingBreadcrumbBuilder::build().
+   *
+   * @see \Drupal\forum\ForumListingBreadcrumbBuilder::build()
+   *
+   * @covers ::build
+   */
+  public function testBuild(): void {
+    // Build all our dependencies, backwards.
+    $translation_manager = $this->getMockBuilder('Drupal\Core\StringTranslation\TranslationInterface')
+      ->disableOriginalConstructor()
+      ->getMock();
+
+    $prophecy = $this->prophesize('Drupal\taxonomy\Entity\Term');
+    $prophecy->label()->willReturn('Something');
+    $prophecy->id()->willReturn(1);
+    $prophecy->getCacheTags()->willReturn(['taxonomy_term:1']);
+    $prophecy->getCacheContexts()->willReturn([]);
+    $prophecy->getCacheMaxAge()->willReturn(Cache::PERMANENT);
+    $term1 = $prophecy->reveal();
+
+    $prophecy = $this->prophesize('Drupal\taxonomy\Entity\Term');
+    $prophecy->label()->willReturn('Something else');
+    $prophecy->id()->willReturn(2);
+    $prophecy->getCacheTags()->willReturn(['taxonomy_term:2']);
+    $prophecy->getCacheContexts()->willReturn([]);
+    $prophecy->getCacheMaxAge()->willReturn(Cache::PERMANENT);
+    $term2 = $prophecy->reveal();
+
+    $term_storage = $this->getMockBuilder(TermStorageInterface::class)->getMock();
+    $term_storage->expects($this->exactly(2))
+      ->method('loadAllParents')
+      ->willReturnOnConsecutiveCalls(
+        [$term1],
+        [$term1, $term2],
+      );
+
+    // The root forum.
+    $prophecy = $this->prophesize('Drupal\taxonomy\VocabularyInterface');
+    $prophecy->label()->willReturn('Fora_is_the_plural_of_forum');
+    $prophecy->id()->willReturn(5);
+    $prophecy->getCacheTags()->willReturn(['taxonomy_vocabulary:5']);
+    $prophecy->getCacheContexts()->willReturn([]);
+    $prophecy->getCacheMaxAge()->willReturn(Cache::PERMANENT);
+    $vocab_storage = $this->createMock('Drupal\Core\Entity\EntityStorageInterface');
+    $vocab_storage->expects($this->any())
+      ->method('load')
+      ->willReturnMap([
+        ['forums', $prophecy->reveal()],
+      ]);
+
+    $entity_type_manager = $this->getMockBuilder(EntityTypeManagerInterface::class)
+      ->disableOriginalConstructor()
+      ->getMock();
+    $entity_type_manager->expects($this->any())
+      ->method('getStorage')
+      ->willReturnMap([
+        ['taxonomy_vocabulary', $vocab_storage],
+        ['taxonomy_term', $term_storage],
+      ]);
+
+    $config_factory = $this->getConfigFactoryStub(
+      [
+        'forum.settings' => [
+          'vocabulary' => 'forums',
+        ],
+      ]
+    );
+
+    $forum_manager = $this->createMock('Drupal\forum\ForumManagerInterface');
+
+    // Build a breadcrumb builder to test.
+    $breadcrumb_builder = new ForumListingBreadcrumbBuilder($entity_type_manager, $config_factory, $forum_manager, $translation_manager);
+
+    // Add a translation manager for t().
+    $translation_manager = $this->getStringTranslationStub();
+    $breadcrumb_builder->setStringTranslation($translation_manager);
+
+    // The forum listing we need a breadcrumb back from.
+    $prophecy = $this->prophesize('Drupal\taxonomy\Entity\Term');
+    $prophecy->label()->willReturn('You_should_not_see_this');
+    $prophecy->id()->willReturn(23);
+    $prophecy->getCacheTags()->willReturn(['taxonomy_term:23']);
+    $prophecy->getCacheContexts()->willReturn([]);
+    $prophecy->getCacheMaxAge()->willReturn(Cache::PERMANENT);
+    $forum_listing = $prophecy->reveal();
+
+    // Our data set.
+    $route_match = $this->createMock('Drupal\Core\Routing\RouteMatchInterface');
+    $route_match->expects($this->exactly(2))
+      ->method('getParameter')
+      ->with('taxonomy_term')
+      ->willReturn($forum_listing);
+
+    // First test.
+    $expected1 = [
+      Link::createFromRoute('Home', '<front>'),
+      Link::createFromRoute('Fora_is_the_plural_of_forum', 'forum.index'),
+      Link::createFromRoute('Something', 'forum.page', ['taxonomy_term' => 1]),
+    ];
+    $breadcrumb = $breadcrumb_builder->build($route_match);
+    $this->assertEquals($expected1, $breadcrumb->getLinks());
+    $this->assertEqualsCanonicalizing(['route'], $breadcrumb->getCacheContexts());
+    $this->assertEqualsCanonicalizing(['taxonomy_term:1', 'taxonomy_term:23', 'taxonomy_vocabulary:5'], $breadcrumb->getCacheTags());
+    $this->assertEqualsCanonicalizing(Cache::PERMANENT, $breadcrumb->getCacheMaxAge());
+
+    // Second test.
+    $expected2 = [
+      Link::createFromRoute('Home', '<front>'),
+      Link::createFromRoute('Fora_is_the_plural_of_forum', 'forum.index'),
+      Link::createFromRoute('Something else', 'forum.page', ['taxonomy_term' => 2]),
+      Link::createFromRoute('Something', 'forum.page', ['taxonomy_term' => 1]),
+    ];
+    $breadcrumb = $breadcrumb_builder->build($route_match);
+    $this->assertEquals($expected2, $breadcrumb->getLinks());
+    $this->assertEqualsCanonicalizing(['route'], $breadcrumb->getCacheContexts());
+    $this->assertEqualsCanonicalizing(['taxonomy_term:1', 'taxonomy_term:2', 'taxonomy_term:23', 'taxonomy_vocabulary:5'], $breadcrumb->getCacheTags());
+    $this->assertEquals(Cache::PERMANENT, $breadcrumb->getCacheMaxAge());
+
+  }
+
+}

core/modules/forum/tests/src/Unit/Breadcrumb/ForumNodeBreadcrumbBuilderTest.php

@@ -0,0 +1,222 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Unit\Breadcrumb;
+
+use Drupal\Core\Cache\Cache;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Link;
+use Drupal\forum\Breadcrumb\ForumNodeBreadcrumbBuilder;
+use Drupal\node\Entity\Node;
+use Drupal\taxonomy\TermStorageInterface;
+use Drupal\Tests\UnitTestCase;
+use Symfony\Component\DependencyInjection\Container;
+
+/**
+ * @coversDefaultClass \Drupal\forum\Breadcrumb\ForumNodeBreadcrumbBuilder
+ * @group forum
+ * @group legacy
+ */
+class ForumNodeBreadcrumbBuilderTest extends UnitTestCase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $cache_contexts_manager = $this->getMockBuilder('Drupal\Core\Cache\Context\CacheContextsManager')
+      ->disableOriginalConstructor()
+      ->getMock();
+    $cache_contexts_manager->method('assertValidTokens')->willReturn(TRUE);
+    $container = new Container();
+    $container->set('cache_contexts_manager', $cache_contexts_manager);
+    \Drupal::setContainer($container);
+  }
+
+  /**
+   * Tests ForumNodeBreadcrumbBuilder::applies().
+   *
+   * @param bool $expected
+   *   ForumNodeBreadcrumbBuilder::applies() expected result.
+   * @param string|null $route_name
+   *   (optional) A route name.
+   * @param array $parameter_map
+   *   (optional) An array of parameter names and values.
+   *
+   * @dataProvider providerTestApplies
+   * @covers ::applies
+   */
+  public function testApplies(bool $expected, ?string $route_name = NULL, array $parameter_map = []): void {
+    // Make some test doubles.
+    $entity_type_manager = $this->createMock(EntityTypeManagerInterface::class);
+    $config_factory = $this->getConfigFactoryStub([]);
+    $map = [];
+    if ($parameter_map) {
+      foreach ($parameter_map as $parameter) {
+        $map[] = [
+          $parameter[0],
+          $parameter[1] === TRUE ? $this->getMockBuilder(Node::class)->disableOriginalConstructor()->getMock() : $parameter[1],
+        ];
+      }
+    }
+
+    $forum_manager = $this->createMock('Drupal\forum\ForumManagerInterface');
+    $forum_manager->expects($this->any())
+      ->method('checkNodeType')
+      ->willReturn(TRUE);
+
+    $translation_manager = $this->createMock('Drupal\Core\StringTranslation\TranslationInterface');
+
+    // Make an object to test.
+    $builder = new ForumNodeBreadcrumbBuilder($entity_type_manager, $config_factory, $forum_manager, $translation_manager);
+
+    $route_match = $this->createMock('Drupal\Core\Routing\RouteMatchInterface');
+    $route_match->expects($this->once())
+      ->method('getRouteName')
+      ->willReturn($route_name);
+    $route_match->expects($this->any())
+      ->method('getParameter')
+      ->willReturnMap($map);
+
+    $this->assertEquals($expected, $builder->applies($route_match));
+  }
+
+  /**
+   * Provides test data for testApplies().
+   *
+   * Note that this test is incomplete, because we can't mock NodeInterface.
+   *
+   * @return \Generator
+   *   Datasets for testApplies(). Structured as such:
+   *   - ForumNodeBreadcrumbBuilder::applies() expected result.
+   *   - ForumNodeBreadcrumbBuilder::applies() $attributes input array.
+   */
+  public static function providerTestApplies(): \Generator {
+    yield [FALSE];
+    yield [FALSE, 'NOT.entity.node.canonical'];
+    yield [FALSE, 'entity.node.canonical'];
+    yield [FALSE, 'entity.node.canonical', [['node', NULL]]];
+    yield [TRUE, 'entity.node.canonical', [['node', TRUE]]];
+  }
+
+  /**
+   * Tests ForumNodeBreadcrumbBuilder::build().
+   *
+   * @see \Drupal\forum\ForumNodeBreadcrumbBuilder::build()
+   * @covers ::build
+   */
+  public function testBuild(): void {
+    // Build all our dependencies, backwards.
+    $translation_manager = $this->getMockBuilder('Drupal\Core\StringTranslation\TranslationInterface')
+      ->disableOriginalConstructor()
+      ->getMock();
+
+    $prophecy = $this->prophesize('Drupal\taxonomy\Entity\Term');
+    $prophecy->label()->willReturn('Something');
+    $prophecy->id()->willReturn(1);
+    $prophecy->getCacheTags()->willReturn(['taxonomy_term:1']);
+    $prophecy->getCacheContexts()->willReturn([]);
+    $prophecy->getCacheMaxAge()->willReturn(Cache::PERMANENT);
+    $term1 = $prophecy->reveal();
+
+    $prophecy = $this->prophesize('Drupal\taxonomy\Entity\Term');
+    $prophecy->label()->willReturn('Something else');
+    $prophecy->id()->willReturn(2);
+    $prophecy->getCacheTags()->willReturn(['taxonomy_term:2']);
+    $prophecy->getCacheContexts()->willReturn([]);
+    $prophecy->getCacheMaxAge()->willReturn(Cache::PERMANENT);
+    $term2 = $prophecy->reveal();
+
+    $forum_manager = $this->getMockBuilder('Drupal\forum\ForumManagerInterface')
+      ->disableOriginalConstructor()
+      ->getMock();
+    $term_storage = $this->getMockBuilder(TermStorageInterface::class)->getMock();
+    $term_storage->expects($this->exactly(2))
+      ->method('loadAllParents')
+      ->willReturnOnConsecutiveCalls(
+        [$term1],
+        [$term1, $term2],
+      );
+
+    $prophecy = $this->prophesize('Drupal\taxonomy\VocabularyInterface');
+    $prophecy->label()->willReturn('Forums');
+    $prophecy->id()->willReturn(5);
+    $prophecy->getCacheTags()->willReturn(['taxonomy_vocabulary:5']);
+    $prophecy->getCacheContexts()->willReturn([]);
+    $prophecy->getCacheMaxAge()->willReturn(Cache::PERMANENT);
+    $vocab_storage = $this->createMock('Drupal\Core\Entity\EntityStorageInterface');
+    $vocab_storage->expects($this->any())
+      ->method('load')
+      ->willReturnMap([
+        ['forums', $prophecy->reveal()],
+      ]);
+
+    $entity_type_manager = $this->getMockBuilder(EntityTypeManagerInterface::class)
+      ->disableOriginalConstructor()
+      ->getMock();
+    $entity_type_manager->expects($this->any())
+      ->method('getStorage')
+      ->willReturnMap([
+        ['taxonomy_vocabulary', $vocab_storage],
+        ['taxonomy_term', $term_storage],
+      ]);
+
+    $config_factory = $this->getConfigFactoryStub(
+      [
+        'forum.settings' => [
+          'vocabulary' => 'forums',
+        ],
+      ]
+    );
+
+    // Build a breadcrumb builder to test.
+    $breadcrumb_builder = new ForumNodeBreadcrumbBuilder($entity_type_manager,
+      $config_factory,
+      $forum_manager,
+      $translation_manager);
+
+    // Add a translation manager for t().
+    $translation_manager = $this->getStringTranslationStub();
+    $breadcrumb_builder->setStringTranslation($translation_manager);
+
+    // The forum node we need a breadcrumb back from.
+    $forum_node = $this->getMockBuilder('Drupal\node\Entity\Node')
+      ->disableOriginalConstructor()
+      ->getMock();
+
+    // Our data set.
+    $route_match = $this->createMock('Drupal\Core\Routing\RouteMatchInterface');
+    $route_match->expects($this->exactly(2))
+      ->method('getParameter')
+      ->with('node')
+      ->willReturn($forum_node);
+
+    // First test.
+    $expected1 = [
+      Link::createFromRoute('Home', '<front>'),
+      Link::createFromRoute('Forums', 'forum.index'),
+      Link::createFromRoute('Something', 'forum.page', ['taxonomy_term' => 1]),
+    ];
+    $breadcrumb = $breadcrumb_builder->build($route_match);
+    $this->assertEquals($expected1, $breadcrumb->getLinks());
+    $this->assertEqualsCanonicalizing(['route'], $breadcrumb->getCacheContexts());
+    $this->assertEqualsCanonicalizing(['taxonomy_term:1', 'taxonomy_vocabulary:5'], $breadcrumb->getCacheTags());
+    $this->assertEquals(Cache::PERMANENT, $breadcrumb->getCacheMaxAge());
+
+    // Second test.
+    $expected2 = [
+      Link::createFromRoute('Home', '<front>'),
+      Link::createFromRoute('Forums', 'forum.index'),
+      Link::createFromRoute('Something else', 'forum.page', ['taxonomy_term' => 2]),
+      Link::createFromRoute('Something', 'forum.page', ['taxonomy_term' => 1]),
+    ];
+    $breadcrumb = $breadcrumb_builder->build($route_match);
+    $this->assertEquals($expected2, $breadcrumb->getLinks());
+    $this->assertEqualsCanonicalizing(['route'], $breadcrumb->getCacheContexts());
+    $this->assertEqualsCanonicalizing(['taxonomy_term:1', 'taxonomy_term:2', 'taxonomy_vocabulary:5'], $breadcrumb->getCacheTags());
+    $this->assertEquals(Cache::PERMANENT, $breadcrumb->getCacheMaxAge());
+  }
+
+}

core/modules/forum/tests/src/Unit/ForumManagerTest.php

@@ -0,0 +1,93 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Unit;
+
+use Drupal\Core\Entity\EntityFieldManagerInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * @coversDefaultClass \Drupal\forum\ForumManager
+ * @group forum
+ * @group legacy
+ */
+class ForumManagerTest extends UnitTestCase {
+
+  /**
+   * Tests ForumManager::getIndex().
+   */
+  public function testGetIndex(): void {
+    $entity_field_manager = $this->createMock(EntityFieldManagerInterface::class);
+    $entity_type_manager = $this->createMock(EntityTypeManagerInterface::class);
+
+    $storage = $this->getMockBuilder('\Drupal\taxonomy\VocabularyStorage')
+      ->disableOriginalConstructor()
+      ->getMock();
+
+    $config_factory = $this->createMock('\Drupal\Core\Config\ConfigFactoryInterface');
+
+    $config = $this->getMockBuilder('\Drupal\Core\Config\Config')
+      ->disableOriginalConstructor()
+      ->getMock();
+
+    $config_factory->expects($this->once())
+      ->method('get')
+      ->willReturn($config);
+
+    $config->expects($this->once())
+      ->method('get')
+      ->willReturn('forums');
+
+    $entity_type_manager->expects($this->once())
+      ->method('getStorage')
+      ->willReturn($storage);
+
+    // This is sufficient for testing purposes.
+    $term = new \stdClass();
+
+    $storage->expects($this->once())
+      ->method('create')
+      ->willReturn($term);
+
+    $connection = $this->getMockBuilder('\Drupal\Core\Database\Connection')
+      ->disableOriginalConstructor()
+      ->getMock();
+
+    $translation_manager = $this->getMockBuilder('\Drupal\Core\StringTranslation\TranslationManager')
+      ->disableOriginalConstructor()
+      ->getMock();
+
+    $comment_manager = $this->getMockBuilder('\Drupal\comment\CommentManagerInterface')
+      ->disableOriginalConstructor()
+      ->getMock();
+
+    $manager = $this->getMockBuilder('\Drupal\forum\ForumManager')
+      ->onlyMethods(['getChildren'])
+      ->setConstructorArgs([
+        $config_factory,
+        $entity_type_manager,
+        $connection,
+        $translation_manager,
+        $comment_manager,
+        $entity_field_manager,
+      ])
+      ->getMock();
+
+    $manager->expects($this->once())
+      ->method('getChildren')
+      ->willReturn([]);
+
+    // Get the index once.
+    $index1 = $manager->getIndex();
+
+    // Get it again. This should not return the previously generated index. If
+    // it does not, then the test will fail as the mocked methods will be called
+    // more than once.
+    $index2 = $manager->getIndex();
+
+    $this->assertEquals($index1, $index2);
+  }
+
+}

core/modules/forum/tests/src/Unit/ForumUninstallValidatorTest.php

@@ -0,0 +1,241 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\forum\Unit;
+
+use Drupal\Core\Url;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * @coversDefaultClass \Drupal\forum\ForumUninstallValidator
+ * @group forum
+ * @group legacy
+ */
+class ForumUninstallValidatorTest extends UnitTestCase {
+
+  /**
+   * @var \Drupal\forum\ForumUninstallValidator|\PHPUnit\Framework\MockObject\MockObject
+   */
+  protected $forumUninstallValidator;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->forumUninstallValidator = $this->getMockBuilder('Drupal\forum\ForumUninstallValidator')
+      ->disableOriginalConstructor()
+      ->onlyMethods(['hasForumNodes', 'hasTermsForVocabulary', 'getForumVocabulary'])
+      ->getMock();
+    $this->forumUninstallValidator->setStringTranslation($this->getStringTranslationStub());
+  }
+
+  /**
+   * @covers ::validate
+   */
+  public function testValidateNotForum(): void {
+    $this->forumUninstallValidator->expects($this->never())
+      ->method('hasForumNodes');
+    $this->forumUninstallValidator->expects($this->never())
+      ->method('hasTermsForVocabulary');
+    $this->forumUninstallValidator->expects($this->never())
+      ->method('getForumVocabulary');
+
+    $module = 'not_forum';
+    $expected = [];
+    $reasons = $this->forumUninstallValidator->validate($module);
+    $this->assertEquals($expected, $reasons);
+  }
+
+  /**
+   * @covers ::validate
+   */
+  public function testValidate(): void {
+    $this->forumUninstallValidator->expects($this->once())
+      ->method('hasForumNodes')
+      ->willReturn(FALSE);
+
+    $vocabulary = $this->createMock('Drupal\taxonomy\VocabularyInterface');
+    $this->forumUninstallValidator->expects($this->once())
+      ->method('getForumVocabulary')
+      ->willReturn($vocabulary);
+
+    $this->forumUninstallValidator->expects($this->once())
+      ->method('hasTermsForVocabulary')
+      ->willReturn(FALSE);
+
+    $module = 'forum';
+    $expected = [];
+    $reasons = $this->forumUninstallValidator->validate($module);
+    $this->assertEquals($expected, $reasons);
+  }
+
+  /**
+   * @covers ::validate
+   */
+  public function testValidateHasForumNodes(): void {
+    $this->forumUninstallValidator->expects($this->once())
+      ->method('hasForumNodes')
+      ->willReturn(TRUE);
+
+    $vocabulary = $this->createMock('Drupal\taxonomy\VocabularyInterface');
+    $this->forumUninstallValidator->expects($this->once())
+      ->method('getForumVocabulary')
+      ->willReturn($vocabulary);
+
+    $this->forumUninstallValidator->expects($this->once())
+      ->method('hasTermsForVocabulary')
+      ->willReturn(FALSE);
+
+    $module = 'forum';
+    $expected = [
+      'To uninstall Forum, first delete all <em>Forum</em> content',
+    ];
+    $reasons = $this->forumUninstallValidator->validate($module);
+    $this->assertEquals($expected, $reasons);
+  }
+
+  /**
+   * @covers ::validate
+   */
+  public function testValidateHasTermsForVocabularyWithNodesAccess(): void {
+    $this->forumUninstallValidator->expects($this->once())
+      ->method('hasForumNodes')
+      ->willReturn(TRUE);
+
+    $url = $this->prophesize(Url::class);
+    $url->toString()->willReturn('/path/to/vocabulary/overview');
+
+    $vocabulary = $this->createMock('Drupal\taxonomy\VocabularyInterface');
+    $vocabulary->expects($this->once())
+      ->method('label')
+      ->willReturn('Vocabulary label');
+    $vocabulary->expects($this->once())
+      ->method('toUrl')
+      ->willReturn($url->reveal());
+    $vocabulary->expects($this->once())
+      ->method('access')
+      ->willReturn(TRUE);
+    $this->forumUninstallValidator->expects($this->once())
+      ->method('getForumVocabulary')
+      ->willReturn($vocabulary);
+
+    $this->forumUninstallValidator->expects($this->once())
+      ->method('hasTermsForVocabulary')
+      ->willReturn(TRUE);
+
+    $module = 'forum';
+    $expected = [
+      'To uninstall Forum, first delete all <em>Forum</em> content',
+      'To uninstall Forum, first delete all <a href="/path/to/vocabulary/overview"><em class="placeholder">Vocabulary label</em></a> terms',
+    ];
+    $reasons = $this->forumUninstallValidator->validate($module);
+    $this->assertEquals($expected, $reasons);
+  }
+
+  /**
+   * @covers ::validate
+   */
+  public function testValidateHasTermsForVocabularyWithNodesNoAccess(): void {
+    $this->forumUninstallValidator->expects($this->once())
+      ->method('hasForumNodes')
+      ->willReturn(TRUE);
+
+    $vocabulary = $this->createMock('Drupal\taxonomy\VocabularyInterface');
+    $vocabulary->expects($this->once())
+      ->method('label')
+      ->willReturn('Vocabulary label');
+    $vocabulary->expects($this->never())
+      ->method('toUrl');
+    $vocabulary->expects($this->once())
+      ->method('access')
+      ->willReturn(FALSE);
+    $this->forumUninstallValidator->expects($this->once())
+      ->method('getForumVocabulary')
+      ->willReturn($vocabulary);
+
+    $this->forumUninstallValidator->expects($this->once())
+      ->method('hasTermsForVocabulary')
+      ->willReturn(TRUE);
+
+    $module = 'forum';
+    $expected = [
+      'To uninstall Forum, first delete all <em>Forum</em> content',
+      'To uninstall Forum, first delete all <em class="placeholder">Vocabulary label</em> terms',
+    ];
+    $reasons = $this->forumUninstallValidator->validate($module);
+    $this->assertEquals($expected, $reasons);
+  }
+
+  /**
+   * @covers ::validate
+   */
+  public function testValidateHasTermsForVocabularyAccess(): void {
+    $this->forumUninstallValidator->expects($this->once())
+      ->method('hasForumNodes')
+      ->willReturn(FALSE);
+
+    $url = $this->prophesize(Url::class);
+    $url->toString()->willReturn('/path/to/vocabulary/overview');
+
+    $vocabulary = $this->createMock('Drupal\taxonomy\VocabularyInterface');
+    $vocabulary->expects($this->once())
+      ->method('toUrl')
+      ->willReturn($url->reveal());
+    $vocabulary->expects($this->once())
+      ->method('label')
+      ->willReturn('Vocabulary label');
+    $vocabulary->expects($this->once())
+      ->method('access')
+      ->willReturn(TRUE);
+    $this->forumUninstallValidator->expects($this->once())
+      ->method('getForumVocabulary')
+      ->willReturn($vocabulary);
+
+    $this->forumUninstallValidator->expects($this->once())
+      ->method('hasTermsForVocabulary')
+      ->willReturn(TRUE);
+
+    $module = 'forum';
+    $expected = [
+      'To uninstall Forum, first delete all <a href="/path/to/vocabulary/overview"><em class="placeholder">Vocabulary label</em></a> terms',
+    ];
+    $reasons = $this->forumUninstallValidator->validate($module);
+    $this->assertEquals($expected, $reasons);
+  }
+
+  /**
+   * @covers ::validate
+   */
+  public function testValidateHasTermsForVocabularyNoAccess(): void {
+    $this->forumUninstallValidator->expects($this->once())
+      ->method('hasForumNodes')
+      ->willReturn(FALSE);
+
+    $vocabulary = $this->createMock('Drupal\taxonomy\VocabularyInterface');
+    $vocabulary->expects($this->once())
+      ->method('label')
+      ->willReturn('Vocabulary label');
+    $vocabulary->expects($this->never())
+      ->method('toUrl');
+    $vocabulary->expects($this->once())
+      ->method('access')
+      ->willReturn(FALSE);
+    $this->forumUninstallValidator->expects($this->once())
+      ->method('getForumVocabulary')
+      ->willReturn($vocabulary);
+
+    $this->forumUninstallValidator->expects($this->once())
+      ->method('hasTermsForVocabulary')
+      ->willReturn(TRUE);
+
+    $module = 'forum';
+    $expected = [
+      'To uninstall Forum, first delete all <em class="placeholder">Vocabulary label</em> terms',
+    ];
+    $reasons = $this->forumUninstallValidator->validate($module);
+    $this->assertEquals($expected, $reasons);
+  }
+
+}