first commit

modules/devel/tests/modules/devel_dumper_test/css/devel_dumper_test.css

@@ -0,0 +1,3 @@
+.some-rule {
+  display: block;
+}

modules/devel/tests/modules/devel_dumper_test/devel_dumper_test.info.yml

@@ -0,0 +1,9 @@
+name: 'Devel dumper test module'
+type: module
+description: 'Test pluggable dumpers.'
+package: Testing
+
+# Information added by Drupal.org packaging script on 2024-06-26
+version: '5.2.1+50-dev'
+project: 'devel'
+datestamp: 1719414589

modules/devel/tests/modules/devel_dumper_test/devel_dumper_test.libraries.yml

@@ -0,0 +1,7 @@
+devel_dumper_test:
+  version: 0
+  css:
+    theme:
+      css/devel_dumper_test.css: {}
+  js:
+    js/devel_dumper_test.js: {}

modules/devel/tests/modules/devel_dumper_test/devel_dumper_test.routing.yml

@@ -0,0 +1,40 @@
+devel_dumper_test.dump:
+  path: '/devel_dumper_test/dump'
+  defaults:
+    _controller: '\Drupal\devel_dumper_test\Controller\DumperTestController::dump'
+    _title: 'Devel Dumper Test'
+  requirements:
+    _permission: 'access devel information'
+
+devel_dumper_test.message:
+  path: '/devel_dumper_test/message'
+  defaults:
+    _controller: '\Drupal\devel_dumper_test\Controller\DumperTestController::message'
+    _title: 'Devel Dumper Test'
+  requirements:
+    _permission: 'access devel information'
+
+devel_dumper_test.export:
+  path: '/devel_dumper_test/export'
+  defaults:
+    _controller: '\Drupal\devel_dumper_test\Controller\DumperTestController::export'
+    _title: 'Devel Dumper Test'
+  requirements:
+    _permission: 'access devel information'
+
+devel_dumper_test.export_renderable:
+  path: '/devel_dumper_test/export_renderable'
+  defaults:
+    _controller: '\Drupal\devel_dumper_test\Controller\DumperTestController::exportRenderable'
+    _title: 'Devel Dumper Test'
+  requirements:
+    _permission: 'access devel information'
+
+devel_dumper_test.debug:
+  path: '/devel_dumper_test/debug'
+  defaults:
+    _controller: '\Drupal\devel_dumper_test\Controller\DumperTestController::debug'
+    _title: 'Devel Dumper Test'
+  requirements:
+    # Specifically give access to all users for testing in testDumpersOutput().
+    _access: 'TRUE'

modules/devel/tests/modules/devel_dumper_test/src/Controller/DumperTestController.php

@@ -0,0 +1,95 @@
+<?php
+
+namespace Drupal\devel_dumper_test\Controller;
+
+use Drupal\Core\Controller\ControllerBase;
+use Drupal\devel\DevelDumperManagerInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Controller class for dumper_test module.
+ *
+ * @package Drupal\devel_dumper_test\Controller
+ */
+class DumperTestController extends ControllerBase {
+
+  /**
+   * The dumper manager.
+   */
+  protected DevelDumperManagerInterface $dumper;
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container): static {
+    $instance = parent::create($container);
+    $instance->dumper = $container->get('devel.dumper');
+
+    return $instance;
+  }
+
+  /**
+   * Returns the dump output to test.
+   *
+   * @return array
+   *   The render array output.
+   */
+  public function dump(): array {
+    $this->dumper->dump('Test output');
+
+    return [
+      '#markup' => 'test',
+    ];
+  }
+
+  /**
+   * Returns the message output to test.
+   *
+   * @return array
+   *   The render array output.
+   */
+  public function message(): array {
+    $this->dumper->message('Test output');
+
+    return [
+      '#markup' => 'test',
+    ];
+  }
+
+  /**
+   * Returns the debug output to test.
+   *
+   * @return array
+   *   The render array output.
+   */
+  public function debug(): array {
+    $this->dumper->debug('Test output');
+
+    return [
+      '#markup' => 'test',
+    ];
+  }
+
+  /**
+   * Returns the export output to test.
+   *
+   * @return array
+   *   The render array output.
+   */
+  public function export(): array {
+    return [
+      '#markup' => $this->dumper->export('Test output'),
+    ];
+  }
+
+  /**
+   * Returns the renderable export output to test.
+   *
+   * @return array
+   *   The render array output.
+   */
+  public function exportRenderable(): array {
+    return $this->dumper->exportAsRenderable('Test output');
+  }
+
+}

modules/devel/tests/modules/devel_dumper_test/src/Plugin/Devel/Dumper/AvailableTestDumper.php

@@ -0,0 +1,63 @@
+<?php
+
+namespace Drupal\devel_dumper_test\Plugin\Devel\Dumper;
+
+use Drupal\Component\Render\MarkupInterface;
+use Drupal\devel\DevelDumperBase;
+
+/**
+ * Provides a AvailableTestDumper plugin.
+ *
+ * @DevelDumper(
+ *   id = "available_test_dumper",
+ *   label = @Translation("Available test dumper."),
+ *   description = @Translation("Drupal dumper for testing purposes (available).")
+ * )
+ */
+class AvailableTestDumper extends DevelDumperBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function dump($input, $name = NULL): void {
+    // Add a predetermined string to $input to check if this dumper has been
+    // selected successfully.
+    $input = '<pre>AvailableTestDumper::dump() ' . $input . '</pre>';
+    echo $input;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function export(mixed $input, ?string $name = NULL): MarkupInterface|string {
+    // Add a predetermined string to $input to check if this dumper has been
+    // selected successfully.
+    $input = '<pre>AvailableTestDumper::export() ' . $input . '</pre>';
+
+    return $this->setSafeMarkup($input);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function exportAsRenderable($input, $name = NULL): array {
+    // Add a predetermined string to $input to check if this dumper has been
+    // selected successfully.
+    $input = '<pre>AvailableTestDumper::exportAsRenderable() ' . $input . '</pre>';
+
+    return [
+      '#attached' => [
+        'library' => ['devel_dumper_test/devel_dumper_test'],
+      ],
+      '#markup' => $this->setSafeMarkup($input),
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function checkRequirements(): bool {
+    return TRUE;
+  }
+
+}

modules/devel/tests/modules/devel_dumper_test/src/Plugin/Devel/Dumper/NotAvailableTestDumper.php

@@ -0,0 +1,43 @@
+<?php
+
+namespace Drupal\devel_dumper_test\Plugin\Devel\Dumper;
+
+use Drupal\Component\Render\MarkupInterface;
+use Drupal\devel\DevelDumperBase;
+
+/**
+ * Provides a NotAvailableTestDumper plugin.
+ *
+ * @DevelDumper(
+ *   id = "not_available_test_dumper",
+ *   label = @Translation("Not available test dumper."),
+ *   description = @Translation("Drupal dumper for testing purposes (not available).")
+ * )
+ */
+class NotAvailableTestDumper extends DevelDumperBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function dump($input, $name = NULL): void {
+    $input = '<pre>' . $input . '</pre>';
+    echo $input;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function export(mixed $input, ?string $name = NULL): MarkupInterface|string {
+    $input = '<pre>' . $input . '</pre>';
+
+    return $this->setSafeMarkup($input);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function checkRequirements(): bool {
+    return FALSE;
+  }
+
+}

modules/devel/tests/modules/devel_entity_test/devel_entity_test.info.yml

@@ -0,0 +1,13 @@
+name: 'Devel entity test module'
+type: module
+description: 'Provides entity types for Devel tests.'
+package: Testing
+dependencies:
+  - drupal:field
+  - drupal:text
+  - drupal:entity_test
+
+# Information added by Drupal.org packaging script on 2024-06-26
+version: '5.2.1+50-dev'
+project: 'devel'
+datestamp: 1719414589

modules/devel/tests/modules/devel_entity_test/devel_entity_test.links.task.yml

@@ -0,0 +1,2 @@
+devel_entity_test.local_tasks:
+  deriver: 'Drupal\devel_entity_test\Plugin\Derivative\DevelEntityTestLocalTasks'

modules/devel/tests/modules/devel_entity_test/devel_entity_test.module

@@ -0,0 +1,35 @@
+<?php
+
+/**
+ * @file
+ * Test module for the entity API providing several entity types for testing.
+ */
+
+/**
+ * Implements hook_entity_view_mode_info_alter().
+ */
+function devel_entity_test_entity_view_mode_info_alter(array &$view_modes): void {
+  $entity_info = \Drupal::entityTypeManager()->getDefinitions();
+  foreach ($entity_info as $entity_type => $info) {
+    if ($info->getProvider() !== 'devel_entity_test_canonical') {
+      continue;
+    }
+
+    if (isset($view_modes[$entity_type])) {
+      continue;
+    }
+
+    $view_modes[$entity_type] = [
+      'full' => [
+        'label' => t('Full object'),
+        'status' => TRUE,
+        'cache' => TRUE,
+      ],
+      'teaser' => [
+        'label' => t('Teaser'),
+        'status' => TRUE,
+        'cache' => TRUE,
+      ],
+    ];
+  }
+}

modules/devel/tests/modules/devel_entity_test/src/Entity/DevelEntityTestCanonical.php

@@ -0,0 +1,44 @@
+<?php
+
+namespace Drupal\devel_entity_test\Entity;
+
+use Drupal\entity_test\Entity\EntityTest;
+
+/**
+ * Defines the test entity class.
+ *
+ * @ContentEntityType(
+ *   id = "devel_entity_test_canonical",
+ *   label = @Translation("Devel test entity with canonical link"),
+ *   handlers = {
+ *     "list_builder" = "Drupal\entity_test\EntityTestListBuilder",
+ *     "view_builder" = "Drupal\entity_test\EntityTestViewBuilder",
+ *     "access" = "Drupal\entity_test\EntityTestAccessControlHandler",
+ *     "form" = {
+ *       "default" = "Drupal\entity_test\EntityTestForm",
+ *       "delete" = "Drupal\entity_test\EntityTestDeleteForm"
+ *     },
+ *     "route_provider" = {
+ *       "html" = "Drupal\Core\Entity\Routing\DefaultHtmlRouteProvider",
+ *     },
+ *     "translation" = "Drupal\content_translation\ContentTranslationHandler",
+ *     "views_data" = "Drupal\entity_test\EntityTestViewsData"
+ *   },
+ *   base_table = "devel_entity_test_canonical",
+ *   persistent_cache = FALSE,
+ *   entity_keys = {
+ *     "id" = "id",
+ *     "uuid" = "uuid",
+ *     "bundle" = "type",
+ *     "label" = "name",
+ *     "langcode" = "langcode",
+ *   },
+ *   links = {
+ *     "canonical" = "/devel_entity_test_canonical/{devel_entity_test_canonical}",
+ *   },
+ *   field_ui_base_route = "entity.entity_test.admin_form",
+ * )
+ */
+class DevelEntityTestCanonical extends EntityTest {
+
+}

modules/devel/tests/modules/devel_entity_test/src/Entity/DevelEntityTestEdit.php

@@ -0,0 +1,44 @@
+<?php
+
+namespace Drupal\devel_entity_test\Entity;
+
+use Drupal\entity_test\Entity\EntityTest;
+
+/**
+ * Defines the test entity class.
+ *
+ * @ContentEntityType(
+ *   id = "devel_entity_test_edit",
+ *   label = @Translation("Devel test entity with edit form link"),
+ *   handlers = {
+ *     "list_builder" = "Drupal\entity_test\EntityTestListBuilder",
+ *     "view_builder" = "Drupal\entity_test\EntityTestViewBuilder",
+ *     "access" = "Drupal\entity_test\EntityTestAccessControlHandler",
+ *     "form" = {
+ *       "default" = "Drupal\entity_test\EntityTestForm",
+ *       "delete" = "Drupal\entity_test\EntityTestDeleteForm"
+ *     },
+ *     "route_provider" = {
+ *       "html" = "Drupal\Core\Entity\Routing\DefaultHtmlRouteProvider",
+ *     },
+ *     "translation" = "Drupal\content_translation\ContentTranslationHandler",
+ *     "views_data" = "Drupal\entity_test\EntityTestViewsData"
+ *   },
+ *   base_table = "devel_entity_test_edit",
+ *   persistent_cache = FALSE,
+ *   entity_keys = {
+ *     "id" = "id",
+ *     "uuid" = "uuid",
+ *     "bundle" = "type",
+ *     "label" = "name",
+ *     "langcode" = "langcode",
+ *   },
+ *   links = {
+ *     "edit-form" = "/devel_entity_test_edit/manage/{devel_entity_test_edit}",
+ *   },
+ *   field_ui_base_route = "entity.entity_test.admin_form",
+ * )
+ */
+class DevelEntityTestEdit extends EntityTest {
+
+}

modules/devel/tests/modules/devel_entity_test/src/Entity/DevelEntityTestNoLinks.php

@@ -0,0 +1,41 @@
+<?php
+
+namespace Drupal\devel_entity_test\Entity;
+
+use Drupal\entity_test\Entity\EntityTest;
+
+/**
+ * Defines the test entity class.
+ *
+ * @ContentEntityType(
+ *   id = "devel_entity_test_no_links",
+ *   label = @Translation("Devel test entity with no links"),
+ *   handlers = {
+ *     "list_builder" = "Drupal\entity_test\EntityTestListBuilder",
+ *     "view_builder" = "Drupal\entity_test\EntityTestViewBuilder",
+ *     "access" = "Drupal\entity_test\EntityTestAccessControlHandler",
+ *     "form" = {
+ *       "default" = "Drupal\entity_test\EntityTestForm",
+ *       "delete" = "Drupal\entity_test\EntityTestDeleteForm"
+ *     },
+ *     "route_provider" = {
+ *       "html" = "Drupal\Core\Entity\Routing\DefaultHtmlRouteProvider",
+ *     },
+ *     "translation" = "Drupal\content_translation\ContentTranslationHandler",
+ *     "views_data" = "Drupal\entity_test\EntityTestViewsData"
+ *   },
+ *   base_table = "devel_entity_test_no_links",
+ *   persistent_cache = FALSE,
+ *   entity_keys = {
+ *     "id" = "id",
+ *     "uuid" = "uuid",
+ *     "bundle" = "type",
+ *     "label" = "name",
+ *     "langcode" = "langcode",
+ *   },
+ *   field_ui_base_route = "entity.entity_test.admin_form",
+ * )
+ */
+class DevelEntityTestNoLinks extends EntityTest {
+
+}

modules/devel/tests/modules/devel_entity_test/src/Plugin/Derivative/DevelEntityTestLocalTasks.php

@@ -0,0 +1,31 @@
+<?php
+
+namespace Drupal\devel_entity_test\Plugin\Derivative;
+
+use Drupal\Component\Plugin\Derivative\DeriverBase;
+
+/**
+ * Defines the local tasks for all the entity_test entities.
+ */
+class DevelEntityTestLocalTasks extends DeriverBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getDerivativeDefinitions($base_plugin_definition) {
+    $this->derivatives = [];
+
+    $this->derivatives['devel_entity_test_canonical.canonical'] = [];
+    $this->derivatives['devel_entity_test_canonical.canonical']['base_route'] = "entity.devel_entity_test_canonical.canonical";
+    $this->derivatives['devel_entity_test_canonical.canonical']['route_name'] = "entity.devel_entity_test_canonical.canonical";
+    $this->derivatives['devel_entity_test_canonical.canonical']['title'] = 'View';
+
+    $this->derivatives['devel_entity_test_edit.edit'] = [];
+    $this->derivatives['devel_entity_test_edit.edit']['base_route'] = "entity.devel_entity_test_edit.edit_form";
+    $this->derivatives['devel_entity_test_edit.edit']['route_name'] = "entity.devel_entity_test_edit.edit_form";
+    $this->derivatives['devel_entity_test_edit.edit']['title'] = 'Edit';
+
+    return parent::getDerivativeDefinitions($base_plugin_definition);
+  }
+
+}

modules/devel/tests/modules/devel_test/devel_test.info.yml

@@ -0,0 +1,9 @@
+name: 'Devel test module'
+type: module
+description: 'Support module for Devel testing.'
+package: Testing
+
+# Information added by Drupal.org packaging script on 2024-06-26
+version: '5.2.1+50-dev'
+project: 'devel'
+datestamp: 1719414589

modules/devel/tests/modules/devel_test/devel_test.module

@@ -0,0 +1,18 @@
+<?php
+
+/**
+ * @file
+ * Helper module for devel test.
+ */
+
+/**
+ * Implements hook_mail().
+ */
+function devel_test_mail($key, array &$message, array $params): void {
+  if ($key === 'devel_mail_log') {
+    $message['subject'] = $params['subject'];
+    $message['body'][] = $params['body'];
+    $message['headers']['From'] = $params['headers']['from'];
+    $message['headers'] += $params['headers']['additional'];
+  }
+}

modules/devel/tests/modules/devel_test/devel_test.routing.yml

@@ -0,0 +1,7 @@
+devel.simple_page:
+  path: '/devel/simple-page'
+  defaults:
+    _controller: '\Drupal\devel_test\Controller\DevelTestController::simplePage'
+    _title: 'Simple Page'
+  requirements:
+    _permission: 'access devel information'

modules/devel/tests/modules/devel_test/devel_test.services.yml

@@ -0,0 +1,7 @@
+services:
+
+  devel_test.test_route_subscriber:
+    class: Drupal\devel_test\Routing\TestRouteSubscriber
+    arguments: ['@state']
+    tags:
+      - { name: event_subscriber }

modules/devel/tests/modules/devel_test/src/Controller/DevelTestController.php

@@ -0,0 +1,35 @@
+<?php
+
+namespace Drupal\devel_test\Controller;
+
+use Drupal\Core\Controller\ControllerBase;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Returns responses for devel module routes.
+ */
+class DevelTestController extends ControllerBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container): static {
+    $instance = parent::create($container);
+    $instance->stringTranslation = $container->get('string_translation');
+
+    return $instance;
+  }
+
+  /**
+   * Returns a simple page output.
+   *
+   * @return array
+   *   A render array.
+   */
+  public function simplePage(): array {
+    return [
+      '#markup' => $this->t('Simple page'),
+    ];
+  }
+
+}

modules/devel/tests/modules/devel_test/src/Routing/TestRouteSubscriber.php

@@ -0,0 +1,36 @@
+<?php
+
+namespace Drupal\devel_test\Routing;
+
+use Drupal\Core\Routing\RouteSubscriberBase;
+use Drupal\Core\State\State;
+use Symfony\Component\Routing\RouteCollection;
+
+/**
+ * Router subscriber class for testing purpose.
+ */
+class TestRouteSubscriber extends RouteSubscriberBase {
+
+  /**
+   * The state store.
+   */
+  protected State $state;
+
+  /**
+   * Constructor method.
+   *
+   * @param \Drupal\Core\State\State $state
+   *   The object State.
+   */
+  public function __construct(State $state) {
+    $this->state = $state;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function alterRoutes(RouteCollection $collection) {
+    $this->state->set('devel_test_route_rebuild', 'Router rebuild fired');
+  }
+
+}

modules/devel/tests/src/Functional/DevelBrowserTestBase.php

@@ -0,0 +1,55 @@
+<?php
+
+namespace Drupal\Tests\devel\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Browser test base class for Devel functional tests.
+ *
+ * DevelCommandsTest should not extend this class so that it can remain
+ * independent and be used as a cut-and-paste example for other developers.
+ */
+abstract class DevelBrowserTestBase extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['devel', 'devel_test', 'block'];
+
+  /**
+   * Admin user.
+   *
+   * @var \Drupal\user\UserInterface
+   */
+  protected $adminUser;
+
+  /**
+   * User with Devel acces but not site admin permission.
+   *
+   * @var \Drupal\user\UserInterface
+   */
+  protected $develUser;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->adminUser = $this->drupalCreateUser([
+      'access devel information',
+      'administer site configuration',
+    ]);
+
+    $this->develUser = $this->drupalCreateUser([
+      'access devel information',
+    ]);
+  }
+
+}

modules/devel/tests/src/Functional/DevelCommandsTest.php

@@ -0,0 +1,47 @@
+<?php
+
+namespace Drupal\Tests\devel\Functional;
+
+use Drupal\devel\Drush\Commands\DevelCommands;
+use Drupal\Tests\BrowserTestBase;
+use Drush\TestTraits\DrushTestTrait;
+
+/**
+ * Test class for the Devel drush commands.
+ *
+ * Note: Drush must be installed. Add it to your require-dev in composer.json.
+ */
+
+/**
+ * @coversDefaultClass \Drupal\devel\Drush\Commands\DevelCommands
+ * @group devel
+ */
+class DevelCommandsTest extends BrowserTestBase {
+
+  use DrushTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['devel'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Tests drush commands.
+   */
+  public function testCommands(): void {
+    $this->drush(DevelCommands::TOKEN, [], ['format' => 'json']);
+    $output = $this->getOutputFromJSON();
+    $tokens = array_column($output, 'token');
+    $this->assertContains('account-name', $tokens);
+
+    $this->drush(DevelCommands::SERVICES, [], ['format' => 'json']);
+    $output = $this->getOutputFromJSON();
+    $this->assertContains('current_user', $output);
+  }
+
+}

modules/devel/tests/src/Functional/DevelContainerInfoTest.php

@@ -0,0 +1,239 @@
+<?php
+
+namespace Drupal\Tests\devel\Functional;
+
+use Drupal\Core\Url;
+use Drupal\devel\Routing\RouteSubscriber;
+
+/**
+ * Tests container info pages and links.
+ *
+ * @group devel
+ */
+class DevelContainerInfoTest extends DevelBrowserTestBase {
+
+  use DevelWebAssertHelper;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->drupalPlaceBlock('local_tasks_block');
+    $this->drupalPlaceBlock('page_title_block');
+    $this->drupalLogin($this->develUser);
+  }
+
+  /**
+   * Tests container info menu link.
+   */
+  public function testContainerInfoMenuLink(): void {
+    $this->drupalPlaceBlock('system_menu_block:devel');
+    // Ensures that the events info link is present on the devel menu and that
+    // it points to the correct page.
+    $this->drupalGet('');
+    $this->clickLink('Container Info');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->addressEquals('/devel/container/service');
+    $this->assertSession()->pageTextContains('Container services');
+  }
+
+  /**
+   * Tests service list page.
+   */
+  public function testServiceList(): void {
+    $this->drupalGet('/devel/container/service');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains('Container services');
+    $this->assertContainerInfoLocalTasks();
+
+    $page = $this->getSession()->getPage();
+
+    // Ensures that the services table is found.
+    $table = $page->find('css', 'table.devel-service-list');
+    $this->assertNotNull($table);
+
+    // Ensures that the expected table headers are found.
+    $headers = $table->findAll('css', 'thead th');
+    $this->assertEquals(4, count($headers));
+
+    $expected_headers = ['ID', 'Class', 'Alias', 'Operations'];
+    $actual_headers = array_map(static fn($element) => $element->getText(), $headers);
+    $this->assertSame($expected_headers, $actual_headers);
+
+    // Ensures that all the services are listed in the table.
+    $cached_definition = \Drupal::service('kernel')->getCachedContainerDefinition();
+    $this->assertNotNull($cached_definition);
+    $rows = $table->findAll('css', 'tbody tr');
+    $this->assertEquals(count($cached_definition['services']), count($rows));
+
+    // Tests the presence of some (arbitrarily chosen) services in the table.
+    $expected_services = [
+// Alias changed in Drupal 10 so commented out the test for now.
+//      'config.factory' => [
+//        'class' => 'Drupal\Core\Config\ConfigFactory',
+//        'alias' => '',
+//      ],
+      'devel.route_subscriber' => [
+        'class' => RouteSubscriber::class,
+        'alias' => '',
+      ],
+//      'plugin.manager.element_info' => [
+//        'class' => 'Drupal\Core\Render\ElementInfoManager',
+//        'alias' => 'element_info',
+//      ],
+    ];
+
+    foreach ($expected_services as $service_id => $expected) {
+      $row = $table->find('css', sprintf('tbody tr:contains("%s")', $service_id));
+      $this->assertNotNull($row);
+
+      $cells = $row->findAll('css', 'td');
+      $this->assertEquals(4, count($cells));
+
+      $cell_service_id = $cells[0];
+      $this->assertEquals($service_id, $cell_service_id->getText());
+      $this->assertTrue($cell_service_id->hasClass('table-filter-text-source'));
+
+      $cell_class = $cells[1];
+      $this->assertEquals($expected['class'], $cell_class->getText());
+      $this->assertTrue($cell_class->hasClass('table-filter-text-source'));
+
+      $cell_alias = $cells[2];
+      $this->assertEquals($expected['alias'], $cell_alias->getText());
+      $this->assertTrue($cell_class->hasClass('table-filter-text-source'));
+
+      $cell_operations = $cells[3];
+      $actual_href = $cell_operations->findLink('Devel')->getAttribute('href');
+      $expected_href = Url::fromRoute('devel.container_info.service.detail', ['service_id' => $service_id])->toString();
+      $this->assertEquals($expected_href, $actual_href);
+    }
+
+    // Ensures that the page is accessible ony to users with the adequate
+    // permissions.
+    $this->drupalLogout();
+    $this->drupalGet('devel/container/service');
+    $this->assertSession()->statusCodeEquals(403);
+  }
+
+  /**
+   * Tests service detail page.
+   */
+  public function testServiceDetail(): void {
+    $service_id = 'devel.dumper';
+
+    // Ensures that the page works as expected.
+    $this->drupalGet('/devel/container/service/' . $service_id);
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains(sprintf('Service %s detail', $service_id));
+
+    // Ensures that the page returns a 404 error if the requested service is
+    // not defined.
+    $this->drupalGet('/devel/container/service/not.exists');
+    $this->assertSession()->statusCodeEquals(404);
+
+    // Ensures that the page is accessible ony to users with the adequate
+    // permissions.
+    $this->drupalLogout();
+    $this->drupalGet('devel/container/service/' . $service_id);
+    $this->assertSession()->statusCodeEquals(403);
+  }
+
+  /**
+   * Tests parameter list page.
+   */
+  public function testParameterList(): void {
+    // Ensures that the page works as expected.
+    $this->drupalGet('/devel/container/parameter');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains('Container parameters');
+    $this->assertContainerInfoLocalTasks();
+
+    $page = $this->getSession()->getPage();
+
+    // Ensures that the parameters table is found.
+    $table = $page->find('css', 'table.devel-parameter-list');
+    $this->assertNotNull($table);
+
+    // Ensures that the expected table headers are found.
+    $headers = $table->findAll('css', 'thead th');
+    $this->assertEquals(2, count($headers));
+
+    $expected_headers = ['Name', 'Operations'];
+    $actual_headers = array_map(static fn($element) => $element->getText(), $headers);
+    $this->assertSame($expected_headers, $actual_headers);
+
+    // Ensures that all the parameters are listed in the table.
+    $cached_definition = \Drupal::service('kernel')->getCachedContainerDefinition();
+    $this->assertNotNull($cached_definition);
+    $rows = $table->findAll('css', 'tbody tr');
+    $this->assertEquals(count($cached_definition['parameters']), count($rows));
+
+    // Tests the presence of some parameters in the table.
+    $expected_parameters = [
+      'container.modules',
+      'cache_bins',
+      'factory.keyvalue',
+      'twig.config',
+    ];
+
+    foreach ($expected_parameters as $parameter_name) {
+      $row = $table->find('css', sprintf('tbody tr:contains("%s")', $parameter_name));
+      $this->assertNotNull($row);
+
+      $cells = $row->findAll('css', 'td');
+      $this->assertEquals(2, count($cells));
+
+      $cell_parameter_name = $cells[0];
+      $this->assertEquals($parameter_name, $cell_parameter_name->getText());
+      $this->assertTrue($cell_parameter_name->hasClass('table-filter-text-source'));
+
+      $cell_operations = $cells[1];
+      $actual_href = $cell_operations->findLink('Devel')->getAttribute('href');
+      $expected_href = Url::fromRoute('devel.container_info.parameter.detail', ['parameter_name' => $parameter_name])->toString();
+      $this->assertEquals($expected_href, $actual_href);
+    }
+
+    // Ensures that the page is accessible ony to users with the adequate
+    // permissions.
+    $this->drupalLogout();
+    $this->drupalGet('devel/container/service');
+    $this->assertSession()->statusCodeEquals(403);
+  }
+
+  /**
+   * Tests parameter detail page.
+   */
+  public function testParameterDetail(): void {
+    $parameter_name = 'cache_bins';
+
+    // Ensures that the page works as expected.
+    $this->drupalGet('/devel/container/parameter/' . $parameter_name);
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains(sprintf('Parameter %s value', $parameter_name));
+
+    // Ensures that the page returns a 404 error if the requested parameter is
+    // not defined.
+    $this->drupalGet('/devel/container/parameter/not_exists');
+    $this->assertSession()->statusCodeEquals(404);
+
+    // Ensures that the page is accessible ony to users with the adequate
+    // permissions.
+    $this->drupalLogout();
+    $this->drupalGet('devel/container/service/' . $parameter_name);
+    $this->assertSession()->statusCodeEquals(403);
+  }
+
+  /**
+   * Asserts that container info local tasks are present.
+   */
+  protected function assertContainerInfoLocalTasks() {
+    $expected_local_tasks = [
+      ['devel.container_info.service', []],
+      ['devel.container_info.parameter', []],
+    ];
+
+    $this->assertLocalTasks($expected_local_tasks);
+  }
+
+}

modules/devel/tests/src/Functional/DevelControllerTest.php

@@ -0,0 +1,189 @@
+<?php
+
+namespace Drupal\Tests\devel\Functional;
+
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\devel_entity_test\Entity\DevelEntityTestCanonical;
+use Drupal\devel_entity_test\Entity\DevelEntityTestEdit;
+use Drupal\devel_entity_test\Entity\DevelEntityTestNoLinks;
+use Drupal\entity_test\Entity\EntityTest;
+
+/**
+ * Tests Devel controller.
+ *
+ * @group devel
+ */
+class DevelControllerTest extends DevelBrowserTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var string[]
+   */
+  protected static $modules = [
+    'devel',
+    'node',
+    'entity_test',
+    'devel_entity_test',
+    'block',
+  ];
+
+  /**
+   * Test entity provided by Core.
+   */
+  protected EntityTest|EntityInterface $entity;
+
+  /**
+   * Devel test entity with canonical link.
+   */
+  protected DevelEntityTestCanonical|EntityInterface $entityCanonical;
+
+  /**
+   * Devel test entity with edit form link.
+   */
+  protected DevelEntityTestEdit|EntityInterface $entityEdit;
+
+  /**
+   * Devel test entity with no links.
+   */
+  protected DevelEntityTestNoLinks|EntityInterface $entityNoLinks;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $entity_type_manager = $this->container->get('entity_type.manager');
+
+    // Create a test entity.
+    $random_label = $this->randomMachineName();
+    $data = ['type' => 'entity_test', 'name' => $random_label];
+    $this->entity = $entity_type_manager->getStorage('entity_test')->create($data);
+    $this->entity->save();
+
+    // Create a test entity with only canonical route.
+    $random_label = $this->randomMachineName();
+    $data = ['type' => 'devel_entity_test_canonical', 'name' => $random_label];
+    $this->entityCanonical = $entity_type_manager->getStorage('devel_entity_test_canonical')->create($data);
+    $this->entityCanonical->save();
+
+    // Create a test entity with only edit route.
+    $random_label = $this->randomMachineName();
+    $data = ['type' => 'devel_entity_test_edit', 'name' => $random_label];
+    $this->entityEdit = $entity_type_manager->getStorage('devel_entity_test_edit')->create($data);
+    $this->entityEdit->save();
+
+    // Create a test entity with no routes.
+    $random_label = $this->randomMachineName();
+    $data = ['type' => 'devel_entity_test_no_links', 'name' => $random_label];
+    $this->entityNoLinks = $entity_type_manager->getStorage('devel_entity_test_no_links')->create($data);
+    $this->entityNoLinks->save();
+
+    $this->drupalPlaceBlock('local_tasks_block');
+
+    $web_user = $this->drupalCreateUser([
+      'view test entity',
+      'administer entity_test content',
+      'access devel information',
+    ]);
+    $this->drupalLogin($web_user);
+  }
+
+  /**
+   * Tests route generation.
+   */
+  public function testRouteGeneration(): void {
+    // Test Devel load and render routes for entities with both route
+    // definitions.
+    $this->drupalGet('entity_test/' . $this->entity->id());
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->LinkExists('View');
+    $this->assertSession()->LinkExists('Edit');
+    $this->assertSession()->LinkExists('Devel');
+    $this->drupalGet('devel/entity_test/' . $this->entity->id());
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->LinkExists('Definition');
+    $this->assertSession()->LinkExists('Render');
+    $this->assertSession()->LinkExists('Load');
+    $this->assertSession()->LinkExists('Load (with references)');
+    $this->assertSession()->LinkExists('Path alias');
+    $this->assertSession()->linkByHrefExists('devel/render/entity_test/' . $this->entity->id());
+    $this->drupalGet('devel/render/entity_test/' . $this->entity->id());
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->linkByHrefExists('devel/definition/entity_test/' . $this->entity->id());
+    $this->drupalGet('devel/definition/entity_test/' . $this->entity->id());
+    $this->assertSession()->statusCodeEquals(200);
+
+    // Test Devel load and render routes for entities with only canonical route
+    // definitions.
+    $this->drupalGet('devel_entity_test_canonical/' . $this->entityCanonical->id());
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->LinkExists('View');
+    $this->assertSession()->LinkNotExists('Edit');
+    $this->assertSession()->LinkExists('Devel');
+    // Use xpath with equality check on @data-drupal-link-system-path because
+    // assertNoLinkByHref matches on partial values and finds the other link.
+    $this->assertSession()->elementNotExists('xpath',
+      '//a[@data-drupal-link-system-path = "devel/devel_entity_test_canonical/' . $this->entityCanonical->id() . '"]');
+    $this->assertSession()->elementExists('xpath',
+      '//a[@data-drupal-link-system-path = "devel/render/devel_entity_test_canonical/' . $this->entityCanonical->id() . '"]');
+    $this->drupalGet('devel/devel_entity_test_canonical/' . $this->entityCanonical->id());
+    // This url used to be '404 not found', but is now '200 OK' following the
+    // generating of devel load links for all entity types.
+    // @see https://gitlab.com/drupalspoons/devel/-/issues/377
+    $this->assertSession()->statusCodeEquals(200);
+    $this->drupalGet('devel/render/devel_entity_test_canonical/' . $this->entityCanonical->id());
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->LinkExists('Definition');
+    $this->assertSession()->LinkExists('Render');
+    $this->assertSession()->LinkNotExists('Load');
+    $this->assertSession()->LinkNotExists('Load (with references)');
+    $this->assertSession()->LinkExists('Path alias');
+    $this->assertSession()->linkByHrefExists('devel/definition/devel_entity_test_canonical/' . $this->entityCanonical->id());
+    $this->drupalGet('devel/definition/devel_entity_test_canonical/' . $this->entityCanonical->id());
+    $this->assertSession()->statusCodeEquals(200);
+
+    // Test Devel load and render routes for entities with only edit route
+    // definitions.
+    $this->drupalGet('devel_entity_test_edit/manage/' . $this->entityEdit->id());
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->LinkNotExists('View');
+    $this->assertSession()->LinkExists('Edit');
+    $this->assertSession()->LinkExists('Devel');
+    $this->assertSession()->linkByHrefExists('devel/devel_entity_test_edit/' . $this->entityEdit->id());
+    $this->drupalGet('devel/devel_entity_test_edit/' . $this->entityEdit->id());
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->LinkExists('Definition');
+    $this->assertSession()->LinkNotExists('Render');
+    $this->assertSession()->LinkExists('Load');
+    $this->assertSession()->LinkExists('Load (with references)');
+    $this->assertSession()->LinkExists('Path alias');
+    $this->assertSession()->linkByHrefExists('devel/definition/devel_entity_test_edit/' . $this->entityEdit->id());
+    $this->assertSession()->linkByHrefNotExists('devel/render/devel_entity_test_edit/' . $this->entityEdit->id());
+    $this->drupalGet('devel/definition/devel_entity_test_edit/' . $this->entityEdit->id());
+    $this->assertSession()->statusCodeEquals(200);
+    $this->drupalGet('devel/render/devel_entity_test_edit/' . $this->entityEdit->id());
+    $this->assertSession()->statusCodeEquals(404);
+
+    // Test Devel load and render routes for entities with no route
+    // definitions.
+    $this->drupalGet('devel_entity_test_no_links/' . $this->entityEdit->id());
+    $this->assertSession()->statusCodeEquals(404);
+    $this->drupalGet('devel/devel_entity_test_no_links/' . $this->entityNoLinks->id());
+    $this->assertSession()->statusCodeEquals(200);
+    $this->drupalGet('devel/render/devel_entity_test_no_links/' . $this->entityNoLinks->id());
+    $this->assertSession()->statusCodeEquals(404);
+    $this->drupalGet('devel/definition/devel_entity_test_no_links/' . $this->entityNoLinks->id());
+    $this->assertSession()->statusCodeEquals(404);
+  }
+
+  /**
+   * Tests the field info page.
+   */
+  public function testFieldInfoPage(): void {
+    $this->drupalGet('/devel/field/info');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains('Field types');
+  }
+
+}

modules/devel/tests/src/Functional/DevelDumperTest.php

@@ -0,0 +1,130 @@
+<?php
+
+namespace Drupal\Tests\devel\Functional;
+
+/**
+ * Tests pluggable dumper feature.
+ *
+ * @group devel
+ */
+class DevelDumperTest extends DevelBrowserTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var string[]
+   */
+  protected static $modules = ['devel', 'devel_dumper_test'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->drupalLogin($this->adminUser);
+  }
+
+  /**
+   * Test dumpers configuration page.
+   */
+  public function testDumpersConfiguration(): void {
+    $this->drupalGet('admin/config/development/devel');
+
+    // Ensures that the dumper input is present on the config page.
+    $this->assertSession()->fieldExists('dumper');
+
+    // No need to ensure that the 'default' dumper is enabled by default via
+    // "checkboxChecked('edit-dumper-default')" since devel_install does dynamic
+    // default.
+    // Ensures that all dumpers (both those declared by devel and by other
+    // modules) are present on the config page and that only the available
+    // dumpers are selectable.
+    $dumpers = [
+      'var_dumper' => 'Symfony var-dumper',
+      'available_test_dumper' => 'Available test dumper',
+      'not_available_test_dumper' => 'Not available test dumper',
+    ];
+    $available_dumpers = ['default', 'var_dumper', 'available_test_dumper'];
+
+    foreach ($dumpers as $dumper => $label) {
+      // Check that a radio option exists for the specified dumper.
+      $this->assertSession()->elementExists('xpath', '//input[@type="radio" and @name="dumper" and @value="' . $dumper . '"]');
+      $this->assertSession()->pageTextContains($label);
+
+      // Check that the available dumpers are enabled and the non-available
+      // dumpers are not enabled.
+      if (in_array($dumper, $available_dumpers)) {
+        $this->assertSession()->elementExists('xpath', '//input[@name="dumper" and not(@disabled="disabled") and @value="' . $dumper . '"]');
+      }
+      else {
+        $this->assertSession()->elementExists('xpath', '//input[@name="dumper" and @disabled="disabled" and @value="' . $dumper . '"]');
+      }
+    }
+
+    // Ensures that saving of the dumpers configuration works as expected.
+    $edit = [
+      'dumper' => 'var_dumper',
+    ];
+    $this->submitForm($edit, 'Save configuration');
+    $this->assertSession()->pageTextContains('The configuration options have been saved.');
+    $this->assertSession()->checkboxChecked('Symfony var-dumper');
+
+    $config = \Drupal::config('devel.settings')->get('devel_dumper');
+    $this->assertEquals('var_dumper', $config, 'The configuration options have been properly saved');
+  }
+
+  /**
+   * Test variable is dumped in page.
+   */
+  public function testDumpersOutput(): void {
+    $edit = [
+      'dumper' => 'available_test_dumper',
+    ];
+    $this->drupalGet('admin/config/development/devel');
+    $this->submitForm($edit, 'Save configuration');
+    $this->assertSession()->pageTextContains('The configuration options have been saved.');
+
+    $this->drupalGet('devel_dumper_test/dump');
+    $elements = $this->xpath('//body/pre[contains(text(), :message)]', [':message' => 'AvailableTestDumper::dump() Test output']);
+    $this->assertNotEmpty($elements, 'Dumped message #1 is present.');
+
+    $this->drupalGet('devel_dumper_test/message');
+    $elements = $this->xpath('//div[@aria-label="Status message"]/pre[contains(text(), :message)]', [':message' => 'AvailableTestDumper::export() Test output']);
+    $this->assertNotEmpty($elements, 'Dumped message #2 is present.');
+
+    $this->drupalGet('devel_dumper_test/export');
+    $elements = $this->xpath('//div[@class="layout-content"]//pre[contains(text(), :message)]', [':message' => 'AvailableTestDumper::export() Test output']);
+    $this->assertNotEmpty($elements, 'Dumped message #3 is present.');
+
+    $this->drupalGet('devel_dumper_test/export_renderable');
+    $elements = $this->xpath('//div[@class="layout-content"]//pre[contains(text(), :message)]', [':message' => 'AvailableTestDumper::exportAsRenderable() Test output']);
+    $this->assertNotEmpty($elements, 'Dumped message #4 is present.');
+    // Ensures that plugins can add libraries to the page when the
+    // ::exportAsRenderable() method is used.
+    $this->assertSession()->responseContains('devel_dumper_test/css/devel_dumper_test.css');
+    $this->assertSession()->responseContains('devel_dumper_test/js/devel_dumper_test.js');
+
+    $debug_filename = \Drupal::service('file_system')->getTempDirectory() . '/' . 'drupal_debug.txt';
+    $this->drupalGet('devel_dumper_test/debug');
+    $file_content = file_get_contents($debug_filename);
+    $expected = <<<EOF
+<pre>AvailableTestDumper::export() Test output</pre>
+
+EOF;
+    $this->assertEquals($file_content, $expected, 'Dumped message #5 is present.');
+
+    // Ensures that the DevelDumperManager::debug() is not access checked and
+    // that the dump is written in the debug file even if the user has not the
+    // 'access devel information' permission.
+    file_put_contents($debug_filename, '');
+    $this->drupalLogout();
+    $this->drupalGet('devel_dumper_test/debug');
+    $file_content = file_get_contents($debug_filename);
+    $expected = <<<EOF
+<pre>AvailableTestDumper::export() Test output</pre>
+
+EOF;
+    $this->assertEquals($file_content, $expected, 'Dumped message #6 is present.');
+  }
+
+}

modules/devel/tests/src/Functional/DevelElementInfoTest.php

@@ -0,0 +1,135 @@
+<?php
+
+namespace Drupal\Tests\devel\Functional;
+
+use Behat\Mink\Element\NodeElement;
+use Drupal\Core\Render\Element\Button;
+use Drupal\Core\Render\Element\Form;
+use Drupal\Core\Render\Element\Html;
+use Drupal\Core\Url;
+
+/**
+ * Tests element info pages and links.
+ *
+ * @group devel
+ */
+class DevelElementInfoTest extends DevelBrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->drupalPlaceBlock('system_menu_block:devel');
+    $this->drupalPlaceBlock('page_title_block');
+    $this->drupalLogin($this->develUser);
+  }
+
+  /**
+   * Tests element info menu link.
+   */
+  public function testElementInfoMenuLink(): void {
+    $this->drupalPlaceBlock('system_menu_block:devel');
+    // Ensures that the element info link is present on the devel menu and that
+    // it points to the correct page.
+    $this->drupalGet('');
+    $this->clickLink('Element Info');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->addressEquals('/devel/elements');
+    $this->assertSession()->pageTextContains('Element Info');
+  }
+
+  /**
+   * Tests element list page.
+   */
+  public function testElementList(): void {
+    $this->drupalGet('/devel/elements');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains('Element Info');
+
+    $page = $this->getSession()->getPage();
+
+    // Ensures that the element list table is found.
+    $table = $page->find('css', 'table.devel-element-list');
+    $this->assertNotNull($table);
+
+    // Ensures that the expected table headers are found.
+    $headers = $table->findAll('css', 'thead th');
+    $this->assertEquals(4, count($headers));
+
+    $expected_headers = ['Name', 'Provider', 'Class', 'Operations'];
+    $actual_headers = array_map(static fn(NodeElement $element) => $element->getText(), $headers);
+    $this->assertSame($expected_headers, $actual_headers);
+
+    // Tests the presence of some (arbitrarily chosen) elements in the table.
+    $expected_elements = [
+      'button' => [
+        'class' => Button::class,
+        'provider' => 'core',
+      ],
+      'form' => [
+        'class' => Form::class,
+        'provider' => 'core',
+      ],
+      'html' => [
+        'class' => Html::class,
+        'provider' => 'core',
+      ],
+    ];
+
+    foreach ($expected_elements as $element_name => $element) {
+      $row = $table->find('css', sprintf('tbody tr:contains("%s")', $element_name));
+      $this->assertNotNull($row);
+
+      $cells = $row->findAll('css', 'td');
+      $this->assertEquals(4, count($cells));
+
+      $cell = $cells[0];
+      $this->assertEquals($element_name, $cell->getText());
+      $this->assertTrue($cell->hasClass('table-filter-text-source'));
+
+      $cell = $cells[1];
+      $this->assertEquals($element['provider'], $cell->getText());
+      $this->assertTrue($cell->hasClass('table-filter-text-source'));
+
+      $cell = $cells[2];
+      $this->assertEquals($element['class'], $cell->getText());
+      $this->assertTrue($cell->hasClass('table-filter-text-source'));
+
+      $cell = $cells[3];
+      $actual_href = $cell->findLink('Devel')->getAttribute('href');
+      $expected_href = Url::fromRoute('devel.elements_page.detail', ['element_name' => $element_name])->toString();
+      $this->assertEquals($expected_href, $actual_href);
+    }
+
+    // Ensures that the page is accessible only to the users with the adequate
+    // permissions.
+    $this->drupalLogout();
+    $this->drupalGet('devel/elements');
+    $this->assertSession()->statusCodeEquals(403);
+  }
+
+  /**
+   * Tests element detail page.
+   */
+  public function testElementDetail(): void {
+    $element_name = 'button';
+
+    // Ensures that the page works as expected.
+    $this->drupalGet('/devel/elements/' . $element_name);
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains('Element ' . $element_name);
+
+    // Ensures that the page returns a 404 error if the requested element is
+    // not defined.
+    $this->drupalGet('/devel/elements/not_exists');
+    $this->assertSession()->statusCodeEquals(404);
+
+    // Ensures that the page is accessible ony to users with the adequate
+    // permissions.
+    $this->drupalLogout();
+    $this->drupalGet('/devel/elements/' . $element_name);
+    $this->assertSession()->statusCodeEquals(403);
+  }
+
+}

modules/devel/tests/src/Functional/DevelEntityTypeInfoTest.php

@@ -0,0 +1,169 @@
+<?php
+
+namespace Drupal\Tests\devel\Functional;
+
+use Behat\Mink\Element\NodeElement;
+use Drupal\Core\Datetime\Entity\DateFormat;
+use Drupal\Core\Entity\Entity\EntityViewMode;
+use Drupal\Core\Url;
+
+/**
+ * Tests entity type info pages and links.
+ *
+ * @group devel
+ */
+class DevelEntityTypeInfoTest extends DevelBrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->drupalPlaceBlock('system_menu_block:devel');
+    $this->drupalPlaceBlock('page_title_block');
+    $this->drupalLogin($this->develUser);
+  }
+
+  /**
+   * Tests entity info menu link.
+   */
+  public function testEntityInfoMenuLink(): void {
+    $this->drupalPlaceBlock('system_menu_block:devel');
+    // Ensures that the entity type info link is present on the devel menu and
+    // that it points to the correct page.
+    $this->drupalGet('');
+    $this->clickLink('Entity Info');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->addressEquals('/devel/entity/info');
+    $this->assertSession()->pageTextContains('Entity Info');
+  }
+
+  /**
+   * Tests entity type list page.
+   */
+  public function testEntityTypeList(): void {
+    $this->drupalGet('/devel/entity/info');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains('Entity Info');
+
+    $page = $this->getSession()->getPage();
+
+    // Ensures that the entity type list table is found.
+    $table = $page->find('css', 'table.devel-entity-type-list');
+    $this->assertNotNull($table);
+
+    // Ensures that the expected table headers are found.
+    $headers = $table->findAll('css', 'thead th');
+    $this->assertEquals(5, count($headers));
+
+    $expected_headers = ['ID', 'Name', 'Provider', 'Class', 'Operations'];
+    $actual_headers = array_map(static fn(NodeElement $element) => $element->getText(), $headers);
+    $this->assertSame($expected_headers, $actual_headers);
+
+    // Tests the presence of some (arbitrarily chosen) entity types in the
+    // table.
+    $expected_types = [
+      'date_format' => [
+        'name' => 'Date format',
+        'class' => DateFormat::class,
+        'provider' => 'core',
+      ],
+      'block' => [
+        'name' => 'Block',
+        'class' => 'Drupal\block\Entity\Block',
+        'provider' => 'block',
+      ],
+      'entity_view_mode' => [
+        'name' => 'View mode',
+        'class' => EntityViewMode::class,
+        'provider' => 'core',
+      ],
+    ];
+
+    foreach ($expected_types as $entity_type_id => $entity_type) {
+      $row = $table->find('css', sprintf('tbody tr:contains("%s")', $entity_type_id));
+      $this->assertNotNull($row);
+
+      $cells = $row->findAll('css', 'td');
+      $this->assertEquals(5, count($cells));
+
+      $cell = $cells[0];
+      $this->assertEquals($entity_type_id, $cell->getText());
+      $this->assertTrue($cell->hasClass('table-filter-text-source'));
+
+      $cell = $cells[1];
+      $this->assertEquals($entity_type['name'], $cell->getText());
+      $this->assertTrue($cell->hasClass('table-filter-text-source'));
+
+      $cell = $cells[2];
+      $this->assertEquals($entity_type['provider'], $cell->getText());
+      $this->assertTrue($cell->hasClass('table-filter-text-source'));
+
+      $cell = $cells[3];
+      $this->assertEquals($entity_type['class'], $cell->getText());
+      $this->assertTrue($cell->hasClass('table-filter-text-source'));
+
+      $cell = $cells[4];
+      $actual_href = $cell->findLink('Devel')->getAttribute('href');
+      $expected_href = Url::fromRoute('devel.entity_info_page.detail', ['entity_type_id' => $entity_type_id])->toString();
+      $this->assertEquals($expected_href, $actual_href);
+
+      $actual_href = $cell->findLink('Fields')->getAttribute('href');
+      $expected_href = Url::fromRoute('devel.entity_info_page.fields', ['entity_type_id' => $entity_type_id])->toString();
+      $this->assertEquals($expected_href, $actual_href);
+    }
+
+    // Ensures that the page is accessible only to the users with the adequate
+    // permissions.
+    $this->drupalLogout();
+    $this->drupalGet('devel/entity/info');
+    $this->assertSession()->statusCodeEquals(403);
+  }
+
+  /**
+   * Tests entity type detail page.
+   */
+  public function testEntityTypeDetail(): void {
+    $entity_type_id = 'date_format';
+
+    // Ensures that the page works as expected.
+    $this->drupalGet('/devel/entity/info/' . $entity_type_id);
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains('Entity type ' . $entity_type_id);
+
+    // Ensures that the page returns a 404 error if the requested entity type is
+    // not defined.
+    $this->drupalGet('/devel/entity/info/not_exists');
+    $this->assertSession()->statusCodeEquals(404);
+
+    // Ensures that the page is accessible ony to users with the adequate
+    // permissions.
+    $this->drupalLogout();
+    $this->drupalGet('/devel/entity/info/' . $entity_type_id);
+    $this->assertSession()->statusCodeEquals(403);
+  }
+
+  /**
+   * Tests entity type fields page.
+   */
+  public function testEntityTypeFields(): void {
+    $entity_type_id = 'date_format';
+
+    // Ensures that the page works as expected.
+    $this->drupalGet('/devel/entity/fields/' . $entity_type_id);
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains('Entity fields ' . $entity_type_id);
+
+    // Ensures that the page returns a 404 error if the requested entity type is
+    // not defined.
+    $this->drupalGet('/devel/entity/fields/not_exists');
+    $this->assertSession()->statusCodeEquals(404);
+
+    // Ensures that the page is accessible ony to users with the adequate
+    // permissions.
+    $this->drupalLogout();
+    $this->drupalGet('/devel/entity/fields/' . $entity_type_id);
+    $this->assertSession()->statusCodeEquals(403);
+  }
+
+}

modules/devel/tests/src/Functional/DevelErrorHandlerTest.php

@@ -0,0 +1,138 @@
+<?php
+
+namespace Drupal\Tests\devel\Functional;
+
+/**
+ * Tests devel error handler.
+ *
+ * @group devel
+ */
+class DevelErrorHandlerTest extends DevelBrowserTestBase {
+
+  /**
+   * Tests devel error handler.
+   */
+  public function testErrorHandler(): void {
+    $messages_selector = '[data-drupal-messages]';
+
+    $expected_notice = 'This is an example notice';
+    $expected_warning = 'This is an example warning';
+
+    $config = $this->config('system.logging');
+    $config->set('error_level', ERROR_REPORTING_DISPLAY_VERBOSE)->save();
+
+    $this->drupalLogin($this->adminUser);
+
+    // Ensures that the error handler config is present on the config page and
+    // by default the standard error handler is selected.
+    $error_handlers = \Drupal::config('devel.settings')->get('error_handlers');
+    $this->assertEquals($error_handlers, [DEVEL_ERROR_HANDLER_STANDARD => DEVEL_ERROR_HANDLER_STANDARD]);
+    $this->drupalGet('admin/config/development/devel');
+    $this->assertTrue($this->assertSession()->optionExists('edit-error-handlers', (string) DEVEL_ERROR_HANDLER_STANDARD)->hasAttribute('selected'));
+
+    // Ensures that selecting the DEVEL_ERROR_HANDLER_NONE option no error
+    // (raw or message) is shown on the site in case of php errors.
+    $edit = [
+      'error_handlers[]' => DEVEL_ERROR_HANDLER_NONE,
+    ];
+    $this->submitForm($edit, 'Save configuration');
+    $this->assertSession()->pageTextContains('The configuration options have been saved.');
+
+    $error_handlers = \Drupal::config('devel.settings')->get('error_handlers');
+    $this->assertEquals($error_handlers, [DEVEL_ERROR_HANDLER_NONE => DEVEL_ERROR_HANDLER_NONE]);
+    $this->assertTrue($this->assertSession()->optionExists('edit-error-handlers', (string) DEVEL_ERROR_HANDLER_NONE)->hasAttribute('selected'));
+
+    $this->clickLink('notice+warning');
+    $this->assertSession()->statusCodeEquals(200);
+    // @todo Two assertions commented out. Can be fixed in conjunction with the following two issues.
+    // @see https://gitlab.com/drupalspoons/devel/-/issues/420
+    // @see https://gitlab.com/drupalspoons/devel/-/issues/454
+    // $this->assertSession()->pageTextNotContains($expected_notice);
+    // $this->assertSession()->pageTextNotContains($expected_warning);
+    $this->assertSession()->elementNotExists('css', $messages_selector);
+
+    // Ensures that selecting the DEVEL_ERROR_HANDLER_BACKTRACE_KINT option a
+    // backtrace above the rendered page is shown on the site in case of php
+    // errors.
+    $edit = [
+      'error_handlers[]' => DEVEL_ERROR_HANDLER_BACKTRACE_KINT,
+    ];
+    $this->submitForm($edit, 'Save configuration');
+    $this->assertSession()->pageTextContains('The configuration options have been saved.');
+
+    $error_handlers = \Drupal::config('devel.settings')->get('error_handlers');
+    $this->assertEquals($error_handlers, [DEVEL_ERROR_HANDLER_BACKTRACE_KINT => DEVEL_ERROR_HANDLER_BACKTRACE_KINT]);
+    $this->assertTrue($this->assertSession()->optionExists('edit-error-handlers', (string) DEVEL_ERROR_HANDLER_BACKTRACE_KINT)->hasAttribute('selected'));
+
+    $this->clickLink('notice+warning');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->elementNotExists('css', $messages_selector);
+
+    // Ensures that selecting the DEVEL_ERROR_HANDLER_BACKTRACE_DPM option a
+    // backtrace in the message area is shown on the site in case of php errors.
+    $edit = [
+      'error_handlers[]' => DEVEL_ERROR_HANDLER_BACKTRACE_DPM,
+    ];
+    $this->submitForm($edit, 'Save configuration');
+    $this->assertSession()->pageTextContains('The configuration options have been saved.');
+
+    $error_handlers = \Drupal::config('devel.settings')->get('error_handlers');
+    $this->assertEquals($error_handlers, [DEVEL_ERROR_HANDLER_BACKTRACE_DPM => DEVEL_ERROR_HANDLER_BACKTRACE_DPM]);
+    $this->assertTrue($this->assertSession()->optionExists('edit-error-handlers', (string) DEVEL_ERROR_HANDLER_BACKTRACE_DPM)->hasAttribute('selected'));
+
+    $this->clickLink('notice+warning');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->elementContains('css', $messages_selector, $expected_notice);
+    $this->assertSession()->elementContains('css', $messages_selector, $expected_warning);
+
+    // Ensures that when multiple handlers are selected, the output produced by
+    // every handler is shown on the site in case of php errors.
+    $edit = [
+      'error_handlers[]' => [
+        DEVEL_ERROR_HANDLER_BACKTRACE_KINT => DEVEL_ERROR_HANDLER_BACKTRACE_KINT,
+        DEVEL_ERROR_HANDLER_BACKTRACE_DPM => DEVEL_ERROR_HANDLER_BACKTRACE_DPM,
+      ],
+    ];
+    $this->submitForm($edit, 'Save configuration');
+    $this->assertSession()->pageTextContains('The configuration options have been saved.');
+
+    $error_handlers = \Drupal::config('devel.settings')->get('error_handlers');
+    $this->assertEquals($error_handlers, [
+      DEVEL_ERROR_HANDLER_BACKTRACE_KINT => DEVEL_ERROR_HANDLER_BACKTRACE_KINT,
+      DEVEL_ERROR_HANDLER_BACKTRACE_DPM => DEVEL_ERROR_HANDLER_BACKTRACE_DPM,
+    ]);
+    $this->assertTrue($this->assertSession()->optionExists('edit-error-handlers', (string) DEVEL_ERROR_HANDLER_BACKTRACE_KINT)->hasAttribute('selected'));
+    $this->assertTrue($this->assertSession()->optionExists('edit-error-handlers', (string) DEVEL_ERROR_HANDLER_BACKTRACE_DPM)->hasAttribute('selected'));
+
+    $this->clickLink('notice+warning');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->elementContains('css', $messages_selector, $expected_notice);
+    $this->assertSession()->elementContains('css', $messages_selector, $expected_warning);
+
+    // Ensures that setting the error reporting to all the output produced by
+    // handlers is shown on the site in case of php errors.
+    $config->set('error_level', ERROR_REPORTING_DISPLAY_ALL)->save();
+    $this->clickLink('notice+warning');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->elementContains('css', $messages_selector, $expected_notice);
+    $this->assertSession()->elementContains('css', $messages_selector, $expected_warning);
+
+    // Ensures that setting the error reporting to some the output produced by
+    // handlers is shown on the site in case of php errors.
+    $config->set('error_level', ERROR_REPORTING_DISPLAY_SOME)->save();
+    $this->clickLink('notice+warning');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->elementContains('css', $messages_selector, $expected_notice);
+    $this->assertSession()->elementContains('css', $messages_selector, $expected_warning);
+
+    // Ensures that setting the error reporting to none the output produced by
+    // handlers is not shown on the site in case of php errors.
+    $config->set('error_level', ERROR_REPORTING_HIDE)->save();
+    $this->clickLink('notice+warning');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextNotContains($expected_notice);
+    $this->assertSession()->pageTextNotContains($expected_warning);
+    $this->assertSession()->elementNotExists('css', $messages_selector);
+  }
+
+}

modules/devel/tests/src/Functional/DevelEventInfoTest.php

@@ -0,0 +1,110 @@
+<?php
+
+namespace Drupal\Tests\devel\Functional;
+
+/**
+ * Tests event info pages and links.
+ *
+ * @group devel
+ */
+class DevelEventInfoTest extends DevelBrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->drupalPlaceBlock('page_title_block');
+    $this->drupalLogin($this->develUser);
+  }
+
+  /**
+   * Tests event info menu link.
+   */
+  public function testEventsInfoMenuLink(): void {
+    $this->drupalPlaceBlock('system_menu_block:devel');
+    // Ensures that the events info link is present on the devel menu and that
+    // it points to the correct page.
+    $this->drupalGet('');
+    $this->clickLink('Events Info');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->addressEquals('/devel/events');
+    $this->assertSession()->pageTextContains('Events');
+  }
+
+  /**
+   * Tests event info page.
+   */
+  public function testEventList(): void {
+    /** @var \Symfony\Component\EventDispatcher\EventDispatcherInterface $event_dispatcher */
+    $event_dispatcher = $this->container->get('event_dispatcher');
+
+    $this->drupalGet('/devel/events');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains('Events');
+
+    $page = $this->getSession()->getPage();
+
+    // Ensures that the event table is found.
+    $table = $page->find('css', 'table.devel-event-list');
+    $this->assertNotNull($table);
+
+    // Ensures that the expected table headers are found.
+    $headers = $table->findAll('css', 'thead th');
+    $this->assertEquals(3, count($headers));
+
+    $expected_headers = ['Event Name', 'Callable', 'Priority'];
+    $actual_headers = array_map(static fn($element) => $element->getText(), $headers);
+    $this->assertSame($expected_headers, $actual_headers);
+
+    // Ensures that all the events are listed in the table.
+    $events = $event_dispatcher->getListeners();
+    $event_header_row = $table->findAll('css', 'tbody tr th.devel-event-name-header');
+    $this->assertEquals(count($events), count($event_header_row));
+
+    // Tests the presence of some (arbitrarily chosen) events and related
+    // listeners in the table. The event items are tested dynamically so no
+    // test failures are expected if listeners change.
+    $expected_events = [
+      'config.delete',
+      'kernel.request',
+      'routing.route_alter',
+    ];
+
+    foreach ($expected_events as $event_name) {
+      // Ensures that the event header is present in the table.
+      $event_header_row = $table->findAll('css', sprintf('tbody tr th:contains("%s")', $event_name));
+      $this->assertTrue(count($event_header_row) >= 1);
+
+      // Ensures that all the event listener are listed in the table.
+      $event_rows = $table->findAll('css', sprintf('tbody tr:contains("%s")', $event_name));
+      // Remove the header row.
+      array_shift($event_rows);
+      $listeners = $event_dispatcher->getListeners($event_name);
+      foreach ($listeners as $index => $listener) {
+        $cells = $event_rows[$index]->findAll('css', 'td');
+        $this->assertEquals(3, count($cells));
+
+        $cell_event_name = $cells[0];
+        $this->assertEquals($event_name, $cell_event_name->getText());
+        $this->assertTrue($cell_event_name->hasClass('table-filter-text-source'));
+        $this->assertTrue($cell_event_name->hasClass('visually-hidden'));
+
+        $cell_callable = $cells[1];
+        is_callable($listener, TRUE, $callable_name);
+        $this->assertEquals($callable_name, $cell_callable->getText());
+
+        $cell_methods = $cells[2];
+        $priority = $event_dispatcher->getListenerPriority($event_name, $listener);
+        $this->assertEquals($priority, $cell_methods->getText());
+      }
+    }
+
+    // Ensures that the page is accessible only to the users with the adequate
+    // permissions.
+    $this->drupalLogout();
+    $this->drupalGet('devel/events');
+    $this->assertSession()->statusCodeEquals(403);
+  }
+
+}

modules/devel/tests/src/Functional/DevelLayoutInfoTest.php

@@ -0,0 +1,140 @@
+<?php
+
+namespace Drupal\Tests\devel\Functional;
+
+/**
+ * Tests layout info pages and links.
+ *
+ * @group devel
+ */
+class DevelLayoutInfoTest extends DevelBrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['devel', 'block', 'layout_discovery'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->drupalPlaceBlock('page_title_block');
+    $this->drupalLogin($this->develUser);
+  }
+
+  /**
+   * Tests layout info menu link.
+   */
+  public function testLayoutsInfoMenuLink(): void {
+    $this->drupalPlaceBlock('system_menu_block:devel');
+    // Ensures that the layout info link is present on the devel menu and that
+    // it points to the correct page.
+    $this->drupalGet('');
+    $this->clickLink('Layouts Info');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->addressEquals('/devel/layouts');
+    $this->assertSession()->pageTextContains('Layout');
+  }
+
+  /**
+   * Tests layout info page.
+   */
+  public function testLayoutList(): void {
+    $this->drupalGet('/devel/layouts');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains('Layouts');
+
+    $page = $this->getSession()->getPage();
+
+    // Ensures that the layout table is found.
+    $table = $page->find('css', 'table.devel-layout-list');
+    $this->assertNotNull($table);
+
+    // Ensures that the expected table headers are found.
+    $headers = $table->findAll('css', 'thead th');
+    $this->assertEquals(6, count($headers));
+
+    $expected_headers = [
+      'Icon',
+      'Label',
+      'Description',
+      'Category',
+      'Regions',
+      'Provider',
+    ];
+    $actual_headers = array_map(static fn($element) => $element->getText(), $headers);
+    $this->assertSame($expected_headers, $actual_headers);
+
+    // Ensures that all the layouts are listed in the table.
+    /** @var \Drupal\Core\Layout\LayoutPluginManagerInterface $layout_manager */
+    $layout_manager = $this->container->get('plugin.manager.core.layout');
+    $layouts = $layout_manager->getDefinitions();
+    $table_rows = $table->findAll('css', 'tbody tr');
+    $this->assertEquals(count($layouts), count($table_rows));
+
+    $index = 0;
+    foreach ($layouts as $layout) {
+      $cells = $table_rows[$index]->findAll('css', 'td');
+      $this->assertEquals(6, count($cells));
+
+      $cell_layout_icon = $cells[0];
+      $icon_path = $layout->getIconPath();
+      if ($icon_path === NULL || $icon_path === '') {
+        // @todo test that the icon path image is set correctly
+      }
+      else {
+        $cell_layout_icon_text = $cell_layout_icon->getText();
+        $this->assertTrue($cell_layout_icon_text === '');
+      }
+
+      $cell_layout_label = $cells[1];
+      $this->assertEquals($cell_layout_label->getText(), $layout->getLabel());
+
+      $cell_layout_description = $cells[2];
+      $this->assertEquals($cell_layout_description->getText(), $layout->getDescription());
+
+      $cell_layout_category = $cells[3];
+      $this->assertEquals($cell_layout_category->getText(), $layout->getCategory());
+
+      $cell_layout_regions = $cells[4];
+      $this->assertEquals($cell_layout_regions->getText(), implode(', ', $layout->getRegionLabels()));
+
+      $cell_layout_provider = $cells[5];
+      $this->assertEquals($cell_layout_provider->getText(), $layout->getProvider());
+
+      ++$index;
+    }
+
+    // Ensures that the page is accessible only to the users with the adequate
+    // permissions.
+    $this->drupalLogout();
+    $this->drupalGet('devel/layouts');
+    $this->assertSession()->statusCodeEquals(403);
+  }
+
+  /**
+   * Tests the dependency with layout_discovery module.
+   */
+  public function testLayoutDiscoveryDependency(): void {
+    $this->container->get('module_installer')->uninstall(['layout_discovery']);
+    $this->drupalPlaceBlock('system_menu_block:devel');
+
+    // Ensures that the layout info link is not present on the devel menu.
+    $this->drupalGet('');
+    $this->assertSession()->linkNotExists('Layouts Info');
+
+    // Ensures that the layouts info page is not available.
+    $this->drupalGet('/devel/layouts');
+    $this->assertSession()->statusCodeEquals(404);
+
+    // Check a few other devel pages to verify devel module stil works.
+    $this->drupalGet('/devel/events');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->drupalGet('devel/routes');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->drupalGet('/devel/container/service');
+    $this->assertSession()->statusCodeEquals(200);
+  }
+
+}

modules/devel/tests/src/Functional/DevelMenuLinksTest.php

@@ -0,0 +1,91 @@
+<?php
+
+namespace Drupal\Tests\devel\Functional;
+
+use Drupal\Core\Url;
+
+/**
+ * Tests devel menu links.
+ *
+ * @group devel
+ */
+class DevelMenuLinksTest extends DevelBrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    // Devel links currently appears only in the devel menu.
+    // Place the devel menu block so we can ensure that these link works
+    // properly.
+    $this->drupalPlaceBlock('system_menu_block:devel');
+    $this->drupalPlaceBlock('page_title_block');
+    $this->drupalLogin($this->adminUser);
+  }
+
+  /**
+   * Tests CSFR protected links.
+   */
+  public function testCsrfProtectedLinks(): void {
+    // Ensure CSRF link are not accessible directly.
+    $this->drupalGet('devel/run-cron');
+    $this->assertSession()->statusCodeEquals(403);
+    $this->drupalGet('devel/cache/clear');
+    $this->assertSession()->statusCodeEquals(403);
+
+    // Ensure clear cache link works properly.
+    $this->assertSession()->linkExists('Cache clear');
+    $this->clickLink('Cache clear');
+    $this->assertSession()->pageTextContains('Cache cleared.');
+
+    // Ensure run cron link works properly.
+    $this->assertSession()->linkExists('Run cron');
+    $this->clickLink('Run cron');
+    $this->assertSession()->pageTextContains('Cron ran successfully.');
+
+    // Ensure CSRF protected links work properly after change session.
+    $this->drupalLogout();
+    $this->drupalLogin($this->adminUser);
+
+    $this->assertSession()->linkExists('Cache clear');
+    $this->clickLink('Cache clear');
+    $this->assertSession()->pageTextContains('Cache cleared.');
+
+    $this->assertSession()->linkExists('Run cron');
+    $this->clickLink('Run cron');
+    $this->assertSession()->pageTextContains('Cron ran successfully.');
+  }
+
+  /**
+   * Tests redirect destination links.
+   */
+  public function testRedirectDestinationLinks(): void {
+    // By default, in the testing profile, front page is the user canonical URI.
+    // For better testing do not use the default frontpage.
+    $url = Url::fromRoute('devel.simple_page');
+
+    $this->drupalGet($url);
+    $this->assertSession()->linkExists('Reinstall Modules');
+    $this->clickLink('Reinstall Modules');
+    $this->assertSession()->addressEquals('devel/reinstall');
+
+    $this->drupalGet($url);
+    $this->assertSession()->linkExists('Rebuild Menu');
+    $this->clickLink('Rebuild Menu');
+    $this->assertSession()->addressEquals('devel/menu/reset');
+
+    $this->drupalGet($url);
+    $this->assertSession()->linkExists('Cache clear');
+    $this->clickLink('Cache clear');
+    $this->assertSession()->pageTextContains('Cache cleared.');
+    $this->assertSession()->addressEquals($url->toString());
+
+    $this->drupalGet($url);
+    $this->assertSession()->linkExists('Run cron');
+    $this->clickLink('Run cron');
+    $this->assertSession()->pageTextContains('Cron ran successfully.');
+    $this->assertSession()->addressEquals($url->toString());
+  }
+
+}

modules/devel/tests/src/Functional/DevelModulesReinstallTest.php

@@ -0,0 +1,51 @@
+<?php
+
+namespace Drupal\Tests\devel\Functional;
+
+/**
+ * Tests reinstall modules.
+ *
+ * @group devel
+ */
+class DevelModulesReinstallTest extends DevelBrowserTestBase {
+
+  /**
+   * The profile to install as a basis for testing.
+   *
+   * @var string
+   */
+  protected $profile = 'minimal';
+
+  /**
+   * Set up test.
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->drupalLogin($this->adminUser);
+  }
+
+  /**
+   * Reinstall modules.
+   */
+  public function testDevelReinstallModules(): void {
+    // Minimal profile enables only dblog, block and node.
+    $modules = ['dblog', 'block'];
+
+    // Needed for compare correctly the message.
+    sort($modules);
+
+    $this->drupalGet('devel/reinstall');
+
+    // Prepare field data in an associative array.
+    $edit = [];
+    foreach ($modules as $module) {
+      $edit[sprintf('reinstall[%s]', $module)] = TRUE;
+    }
+
+    $this->drupalGet('devel/reinstall');
+    $this->submitForm($edit, 'Reinstall');
+    $this->assertSession()->pageTextContains('Uninstalled and installed: ' . implode(', ', $modules) . '.');
+
+  }
+
+}

modules/devel/tests/src/Functional/DevelPathAliasTest.php

@@ -0,0 +1,48 @@
+<?php
+
+namespace Drupal\Tests\devel\Functional;
+
+use Drupal\path_alias\Entity\PathAlias;
+
+/**
+ * Tests the path alias devel page.
+ *
+ * @group devel
+ */
+class DevelPathAliasTest extends DevelBrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['devel', 'node', 'path_alias'];
+
+  public function testPathAliasDevelPage() {
+    $this->drupalGet('devel/path-alias/node/999');
+    $this->assertSession()->statusCodeEquals(404);
+
+    $node = $this->drupalCreateNode();
+    $node_id = $node->id();
+
+    $this->drupalGet('devel/path-alias/node/' . $node_id);
+    $this->assertSession()->statusCodeEquals(403);
+
+    $this->drupalLogin($this->develUser);
+
+    $this->drupalGet('devel/path-alias/node/' . $node_id);
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains('Found no aliases with path "/node/' . $node_id . '".');
+
+    PathAlias::create([
+      'path' => '/node/' . $node_id,
+      'alias' => '/custom-path-1',
+    ])->save();
+    PathAlias::create([
+      'path' => '/node/' . $node_id,
+      'alias' => '/custom-path-2',
+    ])->save();
+
+    $this->drupalGet('devel/path-alias/node/' . $node_id);
+    $this->assertSession()->pageTextContains('Found 2 aliases with path "/node/' . $node_id . '".');
+  }
+
+}

modules/devel/tests/src/Functional/DevelRequirementsTest.php

@@ -0,0 +1,25 @@
+<?php
+
+namespace Drupal\Tests\devel\Functional;
+
+/**
+ * Tests devel requirements.
+ *
+ * @group devel
+ */
+class DevelRequirementsTest extends DevelBrowserTestBase {
+
+  /**
+   * Tests that the status page shows a warning when evel is enabled.
+   */
+  public function testStatusPage(): void {
+    $this->drupalLogin($this->adminUser);
+
+    $this->drupalGet('admin/reports/status');
+    $this->assertSession()->statusCodeEquals(200);
+
+    $this->assertSession()->pageTextContains('Devel module enabled');
+    $this->assertSession()->pageTextContains('The Devel module provides access to internal debugging information; therefore it\'s recommended to disable this module on sites in production.');
+  }
+
+}

modules/devel/tests/src/Functional/DevelRouteInfoTest.php

@@ -0,0 +1,181 @@
+<?php
+
+namespace Drupal\Tests\devel\Functional;
+
+use Drupal\Core\Url;
+
+/**
+ * Tests routes info pages and links.
+ *
+ * @group devel
+ */
+class DevelRouteInfoTest extends DevelBrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->drupalPlaceBlock('system_menu_block:devel');
+    $this->drupalPlaceBlock('page_title_block');
+    $this->drupalLogin($this->develUser);
+  }
+
+  /**
+   * Tests routes info.
+   */
+  public function testRouteList(): void {
+    // Ensures that the routes info link is present on the devel menu and that
+    // it points to the correct page.
+    $this->drupalGet('');
+    $this->clickLink('Routes Info');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->addressEquals('/devel/routes');
+    $this->assertSession()->pageTextContains('Routes');
+
+    $page = $this->getSession()->getPage();
+
+    // Ensures that the expected table headers are found.
+    $headers = $page->findAll('css', 'table.devel-route-list thead th');
+    $this->assertEquals(4, count($headers));
+
+    $expected_items = ['Route Name', 'Path', 'Allowed Methods', 'Operations'];
+    foreach ($headers as $key => $element) {
+      $this->assertSame($element->getText(), $expected_items[$key]);
+    }
+
+    // Ensures that all the routes are listed in the table.
+    $routes = \Drupal::service('router.route_provider')->getAllRoutes();
+    $rows = $page->findAll('css', 'table.devel-route-list tbody tr');
+    $this->assertEquals(count($routes), count($rows));
+
+    // Tests the presence of some (arbitrarily chosen) routes in the table.
+    $expected_routes = [
+      '<current>' => [
+        'path' => '/<current>',
+        'methods' => ['GET', 'POST'],
+        'dynamic' => FALSE,
+      ],
+      'user.login' => [
+        'path' => '/user/login',
+        'methods' => ['GET', 'POST'],
+        'dynamic' => FALSE,
+      ],
+      'entity.user.canonical' => [
+        'path' => '/user/{user}',
+        'methods' => ['GET', 'POST'],
+        'dynamic' => TRUE,
+      ],
+      'entity.user.devel_load' => [
+        'path' => '/devel/user/{user}',
+        'methods' => ['ANY'],
+        'dynamic' => TRUE,
+      ],
+    ];
+
+    foreach ($expected_routes as $route_name => $expected) {
+      $row = $page->find('css', sprintf('table.devel-route-list tbody tr:contains("%s")', $route_name));
+      $this->assertNotNull($row);
+
+      $cells = $row->findAll('css', 'td');
+      $this->assertEquals(4, count($cells));
+
+      $cell_route_name = $cells[0];
+      $this->assertEquals($route_name, $cell_route_name->getText());
+      $this->assertTrue($cell_route_name->hasClass('table-filter-text-source'));
+
+      $cell_path = $cells[1];
+      $this->assertEquals($expected['path'], $cell_path->getText());
+      $this->assertTrue($cell_path->hasClass('table-filter-text-source'));
+
+      $cell_methods = $cells[2];
+      $this->assertEquals(implode('', $expected['methods']), $cell_methods->getText());
+
+      $cell_operations = $cells[3];
+      $actual_href = $cell_operations->findLink('Devel')->getAttribute('href');
+      if ($expected['dynamic']) {
+        $options = ['query' => ['route_name' => $route_name]];
+      }
+      else {
+        $options = ['query' => ['path' => $expected['path']]];
+      }
+
+      $expected_href = Url::fromRoute('devel.route_info.item', [], $options)->toString();
+      $this->assertEquals($expected_href, $actual_href);
+    }
+
+    // Ensures that the page is accessible only to the users with the adequate
+    // permissions.
+    $this->drupalLogout();
+    $this->drupalGet('devel/routes');
+    $this->assertSession()->statusCodeEquals(403);
+  }
+
+  /**
+   * Tests route detail page.
+   */
+  public function testRouteDetail(): void {
+    $expected_title = 'Route detail';
+    $xpath_warning_messages = '//div[@aria-label="Warning message"]';
+
+    // Ensures that devel route detail link in the menu works properly.
+    $url = $this->develUser->toUrl();
+    $path = '/' . $url->getInternalPath();
+
+    $this->drupalGet($url);
+    $this->clickLink('Current route info');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains($expected_title);
+    // Absolute needed due to https://www.drupal.org/project/drupal/issues/3398551#comment-15313236.
+    $expected_url = Url::fromRoute('devel.route_info.item', [], ['absolute' => TRUE, 'query' => ['path' => $path]]);
+    $this->assertSession()->addressEquals($expected_url->toString());
+    $this->assertSession()->elementNotExists('xpath', $xpath_warning_messages);
+
+    // Ensures that devel route detail works properly even when dynamic cache
+    // is enabled.
+    $url = Url::fromRoute('devel.simple_page');
+    $path = '/' . $url->getInternalPath();
+
+    $this->drupalGet($url);
+    $this->clickLink('Current route info');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains($expected_title);
+    $expected_url = Url::fromRoute('devel.route_info.item', [], ['absolute' => TRUE, 'query' => ['path' => $path]]);
+    $this->assertSession()->addressEquals($expected_url->toString());
+    $this->assertSession()->elementNotExists('xpath', $xpath_warning_messages);
+
+    // Ensures that if a non existent path is passed as input, a warning
+    // message is shown.
+    $this->drupalGet('devel/routes/item', ['query' => ['path' => '/undefined']]);
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains($expected_title);
+    $this->assertSession()->elementExists('xpath', $xpath_warning_messages);
+
+    // Ensures that the route detail page works properly when a valid route
+    // name input is passed.
+    $this->drupalGet('devel/routes/item', ['query' => ['route_name' => 'devel.simple_page']]);
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains($expected_title);
+    $this->assertSession()->elementNotExists('xpath', $xpath_warning_messages);
+
+    // Ensures that if a non existent route name is passed as input a warning
+    // message is shown.
+    $this->drupalGet('devel/routes/item', ['query' => ['route_name' => 'not.exists']]);
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains($expected_title);
+    $this->assertSession()->elementExists('xpath', $xpath_warning_messages);
+
+    // Ensures that if no 'path' nor 'name' query string is passed as input,
+    // devel route detail page does not return errors.
+    $this->drupalGet('devel/routes/item');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains($expected_title);
+
+    // Ensures that the page is accessible ony to the users with the adequate
+    // permissions.
+    $this->drupalLogout();
+    $this->drupalGet('devel/routes/item');
+    $this->assertSession()->statusCodeEquals(403);
+  }
+
+}

modules/devel/tests/src/Functional/DevelRouterRebuildTest.php

@@ -0,0 +1,36 @@
+<?php
+
+namespace Drupal\Tests\devel\Functional;
+
+/**
+ * Tests routes rebuild.
+ *
+ * @group devel
+ */
+class DevelRouterRebuildTest extends DevelBrowserTestBase {
+
+  /**
+   * Test routes rebuild.
+   */
+  public function testRouterRebuildConfirmForm(): void {
+    // Reset the state flag.
+    \Drupal::state()->set('devel_test_route_rebuild', NULL);
+
+    $this->drupalGet('devel/menu/reset');
+    $this->assertSession()->statusCodeEquals(403);
+
+    $this->drupalLogin($this->adminUser);
+
+    $this->drupalGet('devel/menu/reset');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains('Are you sure you want to rebuild the router?');
+    $route_rebuild_state = \Drupal::state()->get('devel_test_route_rebuild');
+    $this->assertEmpty($route_rebuild_state);
+
+    $this->submitForm([], 'Rebuild');
+    $this->assertSession()->pageTextContains('The router has been rebuilt.');
+    $route_rebuild_state = \Drupal::state()->get('devel_test_route_rebuild');
+    $this->assertEquals('Router rebuild fired', $route_rebuild_state);
+  }
+
+}

modules/devel/tests/src/Functional/DevelStateEditorTest.php

@@ -0,0 +1,182 @@
+<?php
+
+namespace Drupal\Tests\devel\Functional;
+
+use Behat\Mink\Element\NodeElement;
+
+/**
+ * Tests devel state editor.
+ *
+ * @group devel
+ */
+class DevelStateEditorTest extends DevelBrowserTestBase {
+
+  /**
+   * The state store.
+   *
+   * @var \Drupal\Core\State\StateInterface
+   */
+  protected $state;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->state = $this->container->get('state');
+    $this->drupalPlaceBlock('page_title_block');
+  }
+
+  /**
+   * Tests state editor menu link.
+   */
+  public function testStateEditMenuLink(): void {
+    $this->drupalPlaceBlock('system_menu_block:devel');
+    $this->drupalLogin($this->develUser);
+    // Ensures that the state editor link is present on the devel menu and that
+    // it points to the correct page.
+    $this->drupalGet('');
+    $this->clickLink('State editor');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->addressEquals('/devel/state');
+    $this->assertSession()->pageTextContains('State editor');
+  }
+
+  /**
+   * Tests state listing.
+   */
+  public function testStateListing(): void {
+    $table_selector = 'table.devel-state-list';
+
+    // Ensure that state listing page is accessible only by users with the
+    // adequate permissions.
+    $this->drupalGet('devel/state');
+    $this->assertSession()->statusCodeEquals(403);
+
+    $this->drupalLogin($this->develUser);
+    $this->drupalGet('devel/state');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains('State editor');
+
+    // Ensure that the state variables table is visible.
+    $table = $this->assertSession()->elementExists('css', $table_selector);
+
+    // Ensure that all state variables are listed in the table.
+    $states = \Drupal::keyValue('state')->getAll();
+    $rows = $table->findAll('css', 'tbody tr');
+    $this->assertEquals(count($rows), count($states), 'All states are listed in the table.');
+
+    // Ensure that the added state variables are listed in the table.
+    $this->state->set('devel.simple', 'Hello!');
+    $this->drupalGet('devel/state');
+    $table = $this->assertSession()->elementExists('css', $table_selector);
+    $this->assertSession()->elementExists('css', sprintf('tbody td:contains("%s")', 'devel.simple'), $table);
+
+    // Ensure that the operations column and the actions buttons are not
+    // available for user without 'administer site configuration' permission.
+    $headers = $table->findAll('css', 'thead th');
+    $this->assertEquals(count($headers), 2, 'Correct number of table header cells found.');
+    $this->assertElementsTextEquals($headers, ['Name', 'Value']);
+    $this->assertSession()->elementNotExists('css', 'ul.dropbutton li a', $table);
+
+    // Ensure that the operations column and the actions buttons are
+    // available for user with 'administer site configuration' permission.
+    $this->drupalLogin($this->adminUser);
+    $this->drupalGet('devel/state');
+
+    $table = $this->assertSession()->elementExists('css', $table_selector);
+    $headers = $table->findAll('css', 'thead th');
+    $this->assertEquals(count($headers), 3, 'Correct number of table header cells found.');
+    $this->assertElementsTextEquals($headers, ['Name', 'Value', 'Operations']);
+    $this->assertSession()->elementExists('css', 'ul.dropbutton li a', $table);
+
+    // Test that the edit button works properly.
+    $this->clickLink('Edit');
+    $this->assertSession()->statusCodeEquals(200);
+  }
+
+  /**
+   * Tests state edit.
+   */
+  public function testStateEdit(): void {
+    // Create some state variables for the test.
+    $this->state->set('devel.simple', 0);
+    $this->state->set('devel.array', ['devel' => 'value']);
+    $this->state->set('devel.object', $this->randomObject());
+
+    // Ensure that state edit form is accessible only by users with the
+    // adequate permissions.
+    $this->drupalLogin($this->develUser);
+    $this->drupalGet('devel/state/edit/devel.simple');
+    $this->assertSession()->statusCodeEquals(403);
+
+    $this->drupalLogin($this->adminUser);
+
+    // Ensure that accessing an un-existent state variable cause a warning
+    // message.
+    $this->drupalGet('devel/state/edit/devel.unknown');
+    $this->assertSession()->pageTextContains(strtr('State @name does not exist in the system.', ['@name' => 'devel.unknown']));
+
+    // Ensure that state variables that contain simple type can be edited and
+    // saved.
+    $this->drupalGet('devel/state/edit/devel.simple');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains(strtr('Edit state variable: @name', ['@name' => 'devel.simple']));
+    $input = $this->assertSession()->fieldExists('edit-new-value');
+    $this->assertFalse($input->hasAttribute('disabled'));
+    $button = $this->assertSession()->buttonExists('edit-submit');
+    $this->assertFalse($button->hasAttribute('disabled'));
+
+    $edit = ['new_value' => 1];
+    $this->submitForm($edit, 'Save');
+    $this->assertSession()->pageTextContains(strtr('Variable @name was successfully edited.', ['@name' => 'devel.simple']));
+    $this->assertEquals(1, $this->state->get('devel.simple'));
+
+    // Ensure that state variables that contain array can be edited and saved
+    // and the new value is properly validated.
+    $this->drupalGet('devel/state/edit/devel.array');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains(strtr('Edit state variable: @name', ['@name' => 'devel.array']));
+    $input = $this->assertSession()->fieldExists('edit-new-value');
+    $this->assertFalse($input->hasAttribute('disabled'));
+    $button = $this->assertSession()->buttonExists('edit-submit');
+    $this->assertFalse($button->hasAttribute('disabled'));
+
+    // Try to save an invalid yaml input.
+    $edit = ['new_value' => 'devel: \'value updated'];
+    $this->submitForm($edit, 'Save');
+    $this->assertSession()->pageTextContains('Invalid input:');
+
+    $edit = ['new_value' => 'devel: \'value updated\''];
+    $this->submitForm($edit, 'Save');
+    $this->assertSession()->pageTextContains(strtr('Variable @name was successfully edited.', ['@name' => 'devel.array']));
+    $this->assertEquals(['devel' => 'value updated'], $this->state->get('devel.array'));
+
+    // Ensure that state variables that contain objects cannot be edited.
+    $this->drupalGet('devel/state/edit/devel.object');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains(strtr('Edit state variable: @name', ['@name' => 'devel.object']));
+    $this->assertSession()->pageTextContains(strtr('Only simple structures are allowed to be edited. State @name contains objects.', ['@name' => 'devel.object']));
+    $this->assertSession()->fieldDisabled('edit-new-value');
+    $button = $this->assertSession()->buttonExists('edit-submit');
+    $this->assertTrue($button->hasAttribute('disabled'));
+
+    // Ensure that the cancel link works as expected.
+    $this->clickLink('Cancel');
+    $this->assertSession()->addressEquals('devel/state');
+  }
+
+  /**
+   * Checks that the passed in elements have the expected text.
+   *
+   * @param \Behat\Mink\Element\NodeElement[] $elements
+   *   The elements for which check the text.
+   * @param array $expected_elements_text
+   *   The expected text for the passed in elements.
+   */
+  protected function assertElementsTextEquals(array $elements, array $expected_elements_text) {
+    $actual_text = array_map(static fn(NodeElement $element) => $element->getText(), $elements);
+    $this->assertSame($expected_elements_text, $actual_text);
+  }
+
+}

modules/devel/tests/src/Functional/DevelSwitchUserTest.php

@@ -0,0 +1,323 @@
+<?php
+
+namespace Drupal\Tests\devel\Functional;
+
+use Drupal\Component\Render\FormattableMarkup;
+use Drupal\Core\Session\AccountInterface;
+
+/**
+ * Tests switch user.
+ *
+ * @group devel
+ */
+class DevelSwitchUserTest extends DevelBrowserTestBase {
+
+  /**
+   * The block used by this test.
+   *
+   * @var \Drupal\block\BlockInterface
+   */
+  protected $block;
+
+  /**
+   * The switch user.
+   *
+   * @var \Drupal\user\Entity\User
+   */
+  protected $switchUser;
+
+  /**
+   * The web user.
+   *
+   * @var \Drupal\user\Entity\User
+   */
+  protected $webUser;
+
+  /**
+   * The long user with maximum length username.
+   *
+   * @var \Drupal\user\Entity\User
+   */
+  protected $longUser;
+
+  /**
+   * Set up test.
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->block = $this->drupalPlaceBlock('devel_switch_user', ['id' => 'switch-user', 'label' => 'Switch Hit']);
+
+    $this->develUser = $this->drupalCreateUser(['access devel information', 'switch users'], 'Devel User Four');
+    $this->switchUser = $this->drupalCreateUser(['switch users'], 'Switch User Five');
+    $this->webUser = $this->drupalCreateUser([], 'Web User Six');
+    $this->longUser = $this->drupalCreateUser([], 'Long User Seven name has the maximum length of 60 characters');
+  }
+
+  /**
+   * Tests switch user basic functionality.
+   */
+  public function testSwitchUserFunctionality(): void {
+    $this->drupalLogin($this->webUser);
+
+    $this->drupalGet('');
+    $this->assertSession()->pageTextNotContains($this->block->label());
+
+    // Ensure that a token is required to switch user.
+    $this->drupalGet('/devel/switch/' . $this->webUser->getDisplayName());
+    $this->assertSession()->statusCodeEquals(403);
+
+    $this->drupalLogin($this->develUser);
+
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains($this->block->label());
+
+    // Ensure that if name in not passed the controller returns access denied.
+    $this->drupalGet('/devel/switch');
+    $this->assertSession()->statusCodeEquals(403);
+
+    // Ensure that a token is required to switch user.
+    $this->drupalGet('/devel/switch/' . $this->switchUser->getDisplayName());
+    $this->assertSession()->statusCodeEquals(403);
+
+    // Switch to another user account.
+    $this->drupalGet('/user/' . $this->switchUser->id());
+    $this->clickLink($this->switchUser->getDisplayName());
+    $this->assertSessionByUid($this->switchUser->id());
+    $this->assertNoSessionByUid($this->develUser->id());
+
+    // Switch back to initial account.
+    $this->clickLink($this->develUser->getDisplayName());
+    $this->assertNoSessionByUid($this->switchUser->id());
+    $this->assertSessionByUid($this->develUser->id());
+
+    // Use the search form to switch to another account.
+    $edit = ['userid' => $this->switchUser->getDisplayName()];
+    $this->submitForm($edit, 'Switch');
+    $this->assertSessionByUid($this->switchUser->id());
+    $this->assertNoSessionByUid($this->develUser->id());
+
+    // Use the form with username of the maximum length. Mimic the autofill
+    // result by adding " (userid)" at the end.
+    $edit = ['userid' => $this->longUser->getDisplayName() . sprintf(' (%s)', $this->longUser->id())];
+    $this->submitForm($edit, 'Switch');
+    $this->assertSessionByUid($this->longUser->id());
+    $this->assertNoSessionByUid($this->switchUser->id());
+  }
+
+  /**
+   * Tests the switch user block configuration.
+   */
+  public function testSwitchUserBlockConfiguration(): void {
+    $anonymous = \Drupal::config('user.settings')->get('anonymous');
+
+    // Create some users for the test.
+    for ($i = 0; $i < 12; ++$i) {
+      $this->drupalCreateUser();
+    }
+
+    $this->drupalLogin($this->develUser);
+
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains($this->block->label());
+
+    // Ensure that block default configuration is effectively used. The block
+    // default configuration is the following:
+    // - list_size : 12.
+    // - include_anon : FALSE.
+    // - show_form : TRUE.
+    $this->assertSwitchUserSearchForm();
+    $this->assertSwitchUserListCount(12);
+    $this->assertSwitchUserListNoContainsUser($anonymous);
+
+    // Ensure that changing the list_size configuration property the number of
+    // user displayed in the list change.
+    $this->setBlockConfiguration('list_size', 4);
+    $this->drupalGet('');
+    $this->assertSwitchUserListCount(4);
+
+    // Ensure that changing the include_anon configuration property the
+    // anonymous user is displayed in the list.
+    $this->setBlockConfiguration('include_anon', TRUE);
+    $this->drupalGet('');
+    $this->assertSwitchUserListContainsUser($anonymous);
+
+    // Ensure that changing the show_form configuration property the
+    // form is not displayed.
+    $this->setBlockConfiguration('show_form', FALSE);
+    $this->drupalGet('');
+    $this->assertSwitchUserNoSearchForm();
+  }
+
+  /**
+   * Test the user list items.
+   */
+  public function testSwitchUserListItems(): void {
+    $anonymous = \Drupal::config('user.settings')->get('anonymous');
+
+    $this->setBlockConfiguration('list_size', 2);
+
+    // Login as web user so we are sure that this account is prioritized
+    // in the list if not enough users with 'switch users' permission are
+    // present.
+    $this->drupalLogin($this->webUser);
+
+    $this->drupalLogin($this->develUser);
+    $this->drupalGet('');
+
+    // Ensure that users with 'switch users' permission are prioritized.
+    $this->assertSwitchUserListCount(2);
+    $this->assertSwitchUserListContainsUser($this->develUser->getDisplayName());
+    $this->assertSwitchUserListContainsUser($this->switchUser->getDisplayName());
+
+    // Ensure that blocked users are not shown in the list.
+    $this->switchUser->set('status', 0)->save();
+    $this->drupalGet('');
+    $this->assertSwitchUserListCount(2);
+    $this->assertSwitchUserListContainsUser($this->develUser->getDisplayName());
+    $this->assertSwitchUserListContainsUser($this->webUser->getDisplayName());
+    $this->assertSwitchUserListNoContainsUser($this->switchUser->getDisplayName());
+
+    // Ensure that anonymous user are prioritized if include_anon is set to
+    // true.
+    $this->setBlockConfiguration('include_anon', TRUE);
+    $this->drupalGet('');
+    $this->assertSwitchUserListCount(2);
+    $this->assertSwitchUserListContainsUser($this->develUser->getDisplayName());
+    $this->assertSwitchUserListContainsUser($anonymous);
+
+    // Ensure that the switch user block works properly even if no prioritized
+    // users are found (special handling for user 1).
+    $this->drupalLogout();
+    $this->develUser->delete();
+
+    $this->drupalLogin($this->rootUser);
+    $this->drupalGet('');
+    $this->assertSwitchUserListCount(2);
+    // Removed assertion on rootUser which causes random test failures.
+    // @todo Adjust the tests when user 1 option is completed.
+    // @see https://www.drupal.org/project/devel/issues/3097047
+    // @see https://www.drupal.org/project/devel/issues/3114264
+    $this->assertSwitchUserListContainsUser($anonymous);
+
+    $roleStorage = \Drupal::entityTypeManager()->getStorage('user_role');
+
+    // Ensure that the switch user block works properly even if no roles have
+    // the 'switch users' permission associated (special handling for user 1).
+    /** @var array<string, \Drupal\user\RoleInterface> $roles */
+    $roles = $roleStorage->loadMultiple();
+    unset($roles[AccountInterface::ANONYMOUS_ROLE]);
+    $roles = array_filter($roles, static fn($role): bool => $role->hasPermission('switch users'));
+    $roleStorage->delete($roles);
+
+    $this->drupalGet('');
+    $this->assertSwitchUserListCount(2);
+    // Removed assertion on rootUser which causes random test failures.
+    // @todo Adjust the tests when user 1 option is completed.
+    // @see https://www.drupal.org/project/devel/issues/3097047
+    // @see https://www.drupal.org/project/devel/issues/3114264
+    $this->assertSwitchUserListContainsUser($anonymous);
+  }
+
+  /**
+   * Helper function for verify the number of items shown in the user list.
+   *
+   * @param int $number
+   *   The expected number of items.
+   */
+  public function assertSwitchUserListCount($number): void {
+    $result = $this->xpath('//div[@id=:block]//ul/li/a', [':block' => 'block-switch-user']);
+    $this->assertCount($number, $result);
+  }
+
+  /**
+   * Helper function for verify if the user list contains a username.
+   *
+   * @param string $username
+   *   The username to check.
+   */
+  public function assertSwitchUserListContainsUser($username): void {
+    $result = $this->xpath('//div[@id=:block]//ul/li/a[normalize-space()=:user]', [':block' => 'block-switch-user', ':user' => $username]);
+    $this->assertTrue(count($result) > 0, new FormattableMarkup('User "%user" is included in the switch user list.', ['%user' => $username]));
+  }
+
+  /**
+   * Helper function for verify if the user list not contains a username.
+   *
+   * @param string $username
+   *   The username to check.
+   */
+  public function assertSwitchUserListNoContainsUser($username): void {
+    $result = $this->xpath('//div[@id=:block]//ul/li/a[normalize-space()=:user]', [':block' => 'block-switch-user', ':user' => $username]);
+    $this->assertTrue(count($result) == 0, new FormattableMarkup('User "%user" is not included in the switch user list.', ['%user' => $username]));
+  }
+
+  /**
+   * Helper function for verify if the search form is shown.
+   */
+  public function assertSwitchUserSearchForm(): void {
+    $result = $this->xpath('//div[@id=:block]//form[contains(@class, :form)]', [':block' => 'block-switch-user', ':form' => 'devel-switchuser-form']);
+    $this->assertTrue(count($result) > 0, 'The search form is shown.');
+  }
+
+  /**
+   * Helper function for verify if the search form is not shown.
+   */
+  public function assertSwitchUserNoSearchForm(): void {
+    $result = $this->xpath('//div[@id=:block]//form[contains(@class, :form)]', [':block' => 'block-switch-user', ':form' => 'devel-switchuser-form']);
+    $this->assertTrue(count($result) == 0, 'The search form is not shown.');
+  }
+
+  /**
+   * Protected helper method to set the test block's configuration.
+   */
+  protected function setBlockConfiguration($key, $value) {
+    $block = $this->block->getPlugin();
+    $block->setConfigurationValue($key, $value);
+    $this->block->save();
+  }
+
+  /**
+   * Asserts that there is a session for a given user ID.
+   *
+   * Based off masquarade module.
+   *
+   * @param int $uid
+   *   The user ID for which to find a session record.
+   *
+   * @todo find a cleaner way to do this check.
+   */
+  protected function assertSessionByUid($uid) {
+    $result = \Drupal::database()
+      ->select('sessions')
+      ->fields('sessions', ['uid'])
+      ->condition('uid', $uid)
+      ->execute()->fetchAll();
+
+    // Check that we have some results.
+    $this->assertNotEmpty($result, sprintf('No session found for uid %s', $uid));
+    // If there is more than one session, then that must be unexpected.
+    $this->assertCount(1, $result, sprintf('Found more than one session for uid %s', $uid));
+  }
+
+  /**
+   * Asserts that no session exists for a given uid.
+   *
+   * Based off masquarade module.
+   *
+   * @param int $uid
+   *   The user ID to assert.
+   *
+   * @todo find a cleaner way to do this check.
+   */
+  protected function assertNoSessionByUid($uid) {
+    $result = \Drupal::database()
+      ->select('sessions')
+      ->fields('sessions', ['uid'])
+      ->condition('uid', $uid)
+      ->execute()->fetchAll();
+
+    $this->assertEmpty($result, sprintf('No session for uid %d found.', $uid));
+  }
+
+}

modules/devel/tests/src/Functional/DevelToolbarTest.php

@@ -0,0 +1,264 @@
+<?php
+
+namespace Drupal\Tests\devel\Functional;
+
+use Drupal\Core\Menu\MenuTreeParameters;
+
+/**
+ * Tests devel toolbar module functionality.
+ *
+ * @group devel
+ */
+class DevelToolbarTest extends DevelBrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['devel', 'toolbar', 'block'];
+
+  /**
+   * The user for tests.
+   *
+   * @var \Drupal\user\UserInterface
+   */
+  protected $toolbarUser;
+
+  /**
+   * The default toolbar items.
+   *
+   * @var array
+   */
+  protected $defaultToolbarItems = [
+    'devel.cache_clear',
+    'devel.container_info.service',
+    'devel.admin_settings_link',
+    'devel.menu_rebuild',
+    'devel.reinstall',
+    'devel.route_info',
+    'devel.run_cron',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->drupalPlaceBlock('local_tasks_block');
+    $this->drupalPlaceBlock('page_title_block');
+
+    $this->develUser = $this->drupalCreateUser([
+      'administer site configuration',
+      'access devel information',
+      'access toolbar',
+      'switch users',
+    ]);
+    $this->toolbarUser = $this->drupalCreateUser([
+      'access toolbar',
+      'switch users',
+    ]);
+  }
+
+  /**
+   * Tests configuration form.
+   */
+  public function testConfigurationForm(): void {
+    // Ensures that the page is accessible only to users with the adequate
+    // permissions.
+    $this->drupalGet('admin/config/development/devel/toolbar');
+    $this->assertSession()->statusCodeEquals(403);
+
+    // Ensures that the config page is accessible for users with the adequate
+    // permissions and the Devel toolbar local task and content are shown.
+    $this->drupalLogin($this->develUser);
+    $this->drupalGet('admin/config/development/devel/toolbar');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()
+      ->elementExists('xpath', '//h2[text()="Primary tabs"]/following-sibling::ul//a[contains(text(), "Toolbar Settings")]');
+    $this->assertSession()->elementExists('xpath', '//fieldset[@id="edit-toolbar-items--wrapper"]');
+    $this->assertSession()->pageTextContains('Devel Toolbar Settings');
+
+    // Ensures and that all devel menu links are listed in the configuration
+    // page.
+    foreach ($this->getMenuLinkInfos() as $link) {
+      $this->assertSession()->fieldExists(sprintf('toolbar_items[%s]', $link['id']));
+    }
+
+    // Ensures and that the default configuration items are selected by
+    // default.
+    foreach ($this->defaultToolbarItems as $item) {
+      $this->assertSession()->checkboxChecked(sprintf('toolbar_items[%s]', $item));
+    }
+
+    // Ensures that the configuration save works as expected.
+    $edit = [
+      'toolbar_items[devel.event_info]' => 'devel.event_info',
+      'toolbar_items[devel.theme_registry]' => 'devel.theme_registry',
+    ];
+    $this->submitForm($edit, 'Save configuration');
+    $this->assertSession()->pageTextContains('The configuration options have been saved.');
+
+    $expected_items = array_merge($this->defaultToolbarItems, ['devel.event_info', 'devel.theme_registry']);
+    sort($expected_items);
+    $config_items = \Drupal::config('devel.toolbar.settings')->get('toolbar_items');
+    sort($config_items);
+
+    $this->assertEquals($expected_items, $config_items);
+  }
+
+  /**
+   * Tests cache metadata headers.
+   */
+  public function testCacheHeaders(): void {
+    // Disable user toolbar tab so we can test properly if the devel toolbar
+    // implementation interferes with the page cacheability.
+    \Drupal::service('module_installer')->install(['toolbar_disable_user_toolbar']);
+
+    // The menu is not loaded for users without the adequate permission,
+    // so no cache tags for configuration are added.
+    $this->drupalLogin($this->toolbarUser);
+    $this->assertSession()->responseHeaderNotContains('X-Drupal-Cache-Tags', 'config:devel.toolbar.settings');
+    $this->assertSession()->responseHeaderNotContains('X-Drupal-Cache-Tags', 'config:system.menu.devel');
+
+    // Make sure that the configuration cache tags are present for users with
+    // the adequate permission.
+    $this->drupalLogin($this->develUser);
+    $this->assertSession()->responseHeaderContains('X-Drupal-Cache-Tags', 'config:devel.toolbar.settings');
+    $this->assertSession()->responseHeaderContains('X-Drupal-Cache-Tags', 'config:system.menu.devel');
+
+    // The Devel toolbar implementation should not interfere with the page
+    // cacheability, so you expect a MISS value in the X-Drupal-Dynamic-Cache
+    // header the first time.
+    $this->assertSession()->responseHeaderContains('X-Drupal-Dynamic-Cache', 'MISS');
+
+    // Triggers a page reload and verify that the page is served from the
+    // cache.
+    $this->drupalGet('');
+    $this->assertSession()->responseHeaderContains('X-Drupal-Dynamic-Cache', 'HIT');
+  }
+
+  /**
+   * Tests toolbar integration.
+   */
+  public function testToolbarIntegration(): void {
+    $library_css_url = 'css/devel.toolbar.css';
+    $toolbar_selector = '#toolbar-bar .toolbar-tab';
+    $toolbar_tab_selector = '#toolbar-bar .toolbar-tab a.toolbar-icon-devel';
+    $toolbar_tray_selector = '#toolbar-bar .toolbar-tab #toolbar-item-devel-tray';
+
+    // Ensures that devel toolbar item is accessible only for user with the
+    // adequate permissions.
+    $this->drupalGet('');
+    $this->assertSession()->responseNotContains($library_css_url);
+    $this->assertSession()->elementNotExists('css', $toolbar_selector);
+    $this->assertSession()->elementNotExists('css', $toolbar_tab_selector);
+
+    $this->drupalLogin($this->toolbarUser);
+    $this->assertSession()->responseNotContains($library_css_url);
+    $this->assertSession()->elementExists('css', $toolbar_selector);
+    $this->assertSession()->elementNotExists('css', $toolbar_tab_selector);
+
+    $this->drupalLogin($this->develUser);
+    $this->assertSession()->responseContains($library_css_url);
+    $this->assertSession()->elementExists('css', $toolbar_selector);
+    $this->assertSession()->elementExists('css', $toolbar_tab_selector);
+    $this->assertSession()->elementTextContains('css', $toolbar_tab_selector, 'Devel');
+
+    // Ensures that the configure link in the toolbar is present and point to
+    // the correct page.
+    $this->clickLink('Configure');
+    $this->assertSession()->addressEquals('admin/config/development/devel/toolbar');
+
+    // Ensures that the toolbar tray contains the all the menu links. To the
+    // links not marked as always visible will be assigned a css class that
+    // allow to hide they when the toolbar has horizontal orientation.
+    $this->drupalGet('');
+    $toolbar_tray = $this->assertSession()->elementExists('css', $toolbar_tray_selector);
+
+    $devel_menu_items = $this->getMenuLinkInfos();
+    $toolbar_items = $toolbar_tray->findAll('css', 'ul.toolbar-menu a');
+    $this->assertCount(count($devel_menu_items), $toolbar_items);
+
+    foreach ($devel_menu_items as $link) {
+      $item_selector = sprintf('ul.toolbar-menu a:contains("%s")', $link['title']);
+      $item = $this->assertSession()->elementExists('css', $item_selector, $toolbar_tray);
+      // Only test the url up to the ? as the destination and token parameters
+      // will vary and are not checkable.
+      $this->assertEquals(strtok($link['url'], '?'), strtok($item->getAttribute('href'), '?'));
+
+      $not_visible = !in_array($link['id'], $this->defaultToolbarItems);
+      $this->assertTrue($not_visible === $item->hasClass('toolbar-horizontal-item-hidden'));
+    }
+
+    // Ensures that changing the toolbar settings configuration the changes are
+    // immediately visible.
+    $saved_items = $this->config('devel.toolbar.settings')->get('toolbar_items');
+    $saved_items[] = 'devel.event_info';
+
+    $this->config('devel.toolbar.settings')
+      ->set('toolbar_items', $saved_items)
+      ->save();
+
+    $this->drupalGet('');
+    $toolbar_tray = $this->assertSession()->elementExists('css', $toolbar_tray_selector);
+    $item = $this->assertSession()->elementExists('css', sprintf('ul.toolbar-menu a:contains("%s")', 'Events Info'), $toolbar_tray);
+    $this->assertFalse($item->hasClass('toolbar-horizontal-item-hidden'));
+
+    // Ensures that disabling a menu link it will not more shown in the toolbar
+    // and that the changes are immediately visible.
+    $menu_link_manager = \Drupal::service('plugin.manager.menu.link');
+    $menu_link_manager->updateDefinition('devel.event_info', ['enabled' => FALSE]);
+
+    $this->drupalGet('');
+    $toolbar_tray = $this->assertSession()->elementExists('css', $toolbar_tray_selector);
+    $this->assertSession()->elementNotExists('css', sprintf('ul.toolbar-menu a:contains("%s")', 'Events Info'), $toolbar_tray);
+  }
+
+  /**
+   * Tests devel when toolbar module is not installed.
+   */
+  public function testToolbarModuleNotInstalled(): void {
+    // Ensures that when toolbar module is not installed all works properly.
+    \Drupal::service('module_installer')->uninstall(['toolbar']);
+
+    $this->drupalLogin($this->develUser);
+
+    // Toolbar settings page should respond with 404.
+    $this->drupalGet('admin/config/development/devel/toolbar');
+    $this->assertSession()->statusCodeEquals(404);
+
+    // Primary local task should not contain toolbar tab.
+    $this->drupalGet('admin/config/development/devel');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->elementNotExists('xpath', '//a[contains(text(), "Toolbar Settings")]');
+
+    // Toolbar setting config and devel menu cache tags sholud not present.
+    $this->drupalGet('');
+    $this->assertSession()->responseHeaderNotContains('X-Drupal-Cache-Tags', 'config:devel.toolbar.settings');
+    $this->assertSession()->responseHeaderNotContains('X-Drupal-Cache-Tags', 'config:system.menu.devel');
+  }
+
+  /**
+   * Helper function for retrieve the menu link informations.
+   *
+   * @return array
+   *   An array containing the menu link informations.
+   */
+  protected function getMenuLinkInfos() {
+    $parameters = new MenuTreeParameters();
+    $parameters->onlyEnabledLinks()->setTopLevelOnly();
+    $tree = \Drupal::menuTree()->load('devel', $parameters);
+
+    $links = [];
+    foreach ($tree as $element) {
+      $links[] = [
+        'id' => $element->link->getPluginId(),
+        'title' => $element->link->getTitle(),
+        'url' => $element->link->getUrlObject()->toString(),
+      ];
+    }
+
+    return $links;
+  }
+
+}

modules/devel/tests/src/Functional/DevelWebAssertHelper.php

@@ -0,0 +1,34 @@
+<?php
+
+namespace Drupal\Tests\devel\Functional;
+
+use Drupal\Core\Url;
+
+/**
+ * Provides convenience methods for assertions in browser tests.
+ */
+trait DevelWebAssertHelper {
+
+  /**
+   * Asserts local tasks in the page output.
+   *
+   * @param array $routes
+   *   A list of expected local tasks, prepared as an array of route names and
+   *   their associated route parameters, to assert on the page (in the given
+   *   order).
+   * @param int $level
+   *   (optional) The local tasks level to assert; 0 for primary, 1 for
+   *   secondary. Defaults to 0.
+   */
+  protected function assertLocalTasks(array $routes, $level = 0) {
+    $tab_label = $level == 0 ? 'Primary tabs' : 'Secondary tabs';
+    $elements = $this->xpath('//h2[text()="' . $tab_label . '"]/following-sibling::ul//a');
+    $this->assertNotEmpty($elements, 'Local tasks not found.');
+    foreach ($routes as $index => $route_info) {
+      [$route_name, $route_parameters] = $route_info;
+      $expected = Url::fromRoute($route_name, $route_parameters)->toString();
+      $this->assertEquals($expected, $elements[$index]->getAttribute('href'));
+    }
+  }
+
+}

modules/devel/tests/src/Kernel/DevelDumperTestTrait.php

@@ -0,0 +1,133 @@
+<?php
+
+namespace Drupal\Tests\devel\Kernel;
+
+/**
+ * Provides a class for checking dumper output.
+ */
+trait DevelDumperTestTrait {
+
+  /**
+   * Assertion for ensure dump content.
+   *
+   * Asserts that the string passed in input is equals to the string
+   * representation of a variable obtained exporting the data.
+   *
+   * Use \Drupal\devel\DevelDumperManager::export().
+   *
+   * @param string $dump
+   *   The string that contains the dump output to test.
+   * @param mixed $data
+   *   The variable to dump.
+   * @param string $name
+   *   (optional) The label to output before variable, defaults to NULL.
+   * @param string $message
+   *   (optional) A message to display with the assertion.
+   */
+  public function assertDumpExportEquals($dump, mixed $data, $name = NULL, $message = ''): void {
+    $output = $this->getDumperExportDump($data, $name);
+    $this->assertEquals(rtrim($dump), $output, $message);
+  }
+
+  /**
+   * Asserts that a haystack contains the dump export output.
+   *
+   * Use \Drupal\devel\DevelDumperManager::export().
+   *
+   * @param string $haystack
+   *   The string that contains the dump output to test.
+   * @param mixed $data
+   *   The variable to dump.
+   * @param string $name
+   *   (optional) The label to output before variable, defaults to NULL.
+   * @param string $message
+   *   (optional) A message to display with the assertion.
+   */
+  public function assertContainsDumpExport($haystack, mixed $data, $name = NULL, $message = ''): void {
+    // As at 18.04.2020 assertContainsDumpExport() is not actually used in any
+    // devel tests in any current code branch.
+    $output = $this->getDumperExportDump($data, $name);
+    $this->assertStringContainsString($output, (string) $haystack, $message);
+  }
+
+  /**
+   * Assertion for ensure dump content.
+   *
+   * Asserts that the string passed in input is equals to the string
+   * representation of a variable obtained dumping the data.
+   *
+   * Use \Drupal\devel\DevelDumperManager::dump().
+   *
+   * @param string $dump
+   *   The string that contains the dump output to test.
+   * @param mixed $data
+   *   The variable to dump.
+   * @param string $name
+   *   (optional) The label to output before variable, defaults to NULL.
+   * @param string $message
+   *   (optional) A message to display with the assertion.
+   */
+  public function assertDumpEquals($dump, mixed $data, $name = NULL, $message = ''): void {
+    $output = $this->getDumperDump($data, $name);
+    $this->assertEquals(rtrim($dump), $output, $message);
+  }
+
+  /**
+   * Asserts that a haystack contains the dump output.
+   *
+   * Use \Drupal\devel\DevelDumperManager::dump().
+   *
+   * @param string $haystack
+   *   The string that contains the dump output to test.
+   * @param mixed $data
+   *   The variable to dump.
+   * @param string $name
+   *   (optional) The label to output before variable, defaults to NULL.
+   * @param string $message
+   *   (optional) A message to display with the assertion.
+   */
+  public function assertContainsDump($haystack, mixed $data, $name = NULL, $message = ''): void {
+    $output = $this->getDumperDump($data, $name);
+    $this->assertStringContainsString($output, (string) $haystack, $message);
+  }
+
+  /**
+   * Returns a string representation of a variable.
+   *
+   * @param mixed $input
+   *   The variable to dump.
+   * @param string $name
+   *   (optional) The label to output before variable, defaults to NULL.
+   *
+   * @return string
+   *   String representation of a variable.
+   *
+   * @see \Drupal\devel\DevelDumperManager::export()
+   */
+  private function getDumperExportDump(mixed $input, $name = NULL): string {
+    $output = \Drupal::service('devel.dumper')->export($input, $name);
+    return rtrim($output);
+  }
+
+  /**
+   * Returns a string representation of a variable.
+   *
+   * @param mixed $input
+   *   The variable to dump.
+   * @param string $name
+   *   (optional) The label to output before variable, defaults to NULL.
+   *
+   * @return string
+   *   String representation of a variable.
+   *
+   * @see \Drupal\devel\DevelDumperManager::dump()
+   */
+  private function getDumperDump(mixed $input, $name = NULL): string {
+    ob_start();
+    \Drupal::service('devel.dumper')->dump($input, $name);
+    $output = ob_get_contents();
+    ob_end_clean();
+    return rtrim($output);
+  }
+
+}

modules/devel/tests/src/Kernel/DevelEnforcedDependenciesTest.php

@@ -0,0 +1,80 @@
+<?php
+
+namespace Drupal\Tests\devel\Kernel;
+
+use Drupal\block\Entity\Block;
+use Drupal\KernelTests\KernelTestBase;
+use Drupal\system\Entity\Menu;
+
+/**
+ * Tests Devel enforced dependencies.
+ *
+ * @group devel
+ */
+class DevelEnforcedDependenciesTest extends KernelTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var string[]
+   */
+  protected static $modules = ['devel', 'block', 'user', 'system'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->installEntitySchema('user');
+    $this->installConfig('devel');
+    // For uninstall to work.
+    $this->installSchema('user', ['users_data']);
+  }
+
+  /**
+   * Tests devel menu enforced dependencies.
+   */
+  public function testMenuEnforcedDependencies(): void {
+    /** @var \Drupal\Core\Config\ConfigManagerInterface $config_manager */
+    $config_manager = $this->container->get('config.manager');
+
+    // Ensure that the Devel menu has explicit enforced dependencies on devel
+    // module.
+    $menu = Menu::load('devel');
+    $this->assertEquals(['enforced' => ['module' => ['devel']]], $menu->get('dependencies'));
+
+    // Creates an instance of devel menu block so you can test if enforced
+    // dependencies work properly with it.
+    $block_id = strtolower($this->randomMachineName(8));
+
+    $block = Block::create([
+      'plugin' => 'system_menu_block:devel',
+      'region' => 'sidebar_first',
+      'id' => $block_id,
+      'theme' => $this->config('system.theme')->get('default'),
+      'label' => $this->randomMachineName(8),
+      'visibility' => [],
+      'weight' => 0,
+    ]);
+    $block->save();
+
+    // Ensure that the menu and block instance depend on devel module.
+    $dependents = $config_manager->findConfigEntityDependencies('module', ['devel']);
+    $this->assertArrayHasKey('system.menu.devel', $dependents);
+    $this->assertArrayHasKey('block.block.' . $block_id, $dependents);
+
+    $this->container->get('module_installer')->uninstall(['devel']);
+
+    // Ensure that the menu and block instance are deleted when the dependency
+    // is uninstalled.
+    $this->assertNull(Menu::load('devel'));
+    $this->assertNull(Block::load($block_id));
+
+    // Ensure that no config entities depend on devel once uninstalled.
+    $dependents = $config_manager->findConfigEntityDependencies('module', ['devel']);
+    $this->assertArrayNotHasKey('system.menu.devel', $dependents);
+    $this->assertArrayNotHasKey('block.block.' . $block_id, $dependents);
+  }
+
+}

modules/devel/tests/src/Kernel/DevelEntityToArrayTest.php

@@ -0,0 +1,116 @@
+<?php
+
+namespace Drupal\Tests\devel\Kernel;
+
+use Drupal\Core\Field\FieldStorageDefinitionInterface;
+use Drupal\KernelTests\Core\Entity\EntityKernelTestBase;
+use Drupal\Tests\field\Traits\EntityReferenceFieldCreationTrait;
+
+/**
+ * Test Load with References.
+ *
+ * @group devel
+ */
+class DevelEntityToArrayTest extends EntityKernelTestBase {
+
+  use EntityReferenceFieldCreationTrait;
+
+  /**
+   * The entity type used in this test.
+   *
+   * @var string
+   */
+  protected $entityType = 'entity_test';
+
+  /**
+   * The entity type that is being referenced.
+   *
+   * @var string
+   */
+  protected $referencedEntityType = 'entity_test_rev';
+
+  /**
+   * The bundle used in this test.
+   *
+   * @var string
+   */
+  protected $bundle = 'entity_test';
+
+  /**
+   * The name of the field used in this test.
+   *
+   * @var string
+   */
+  protected $fieldName = 'field_test';
+
+  /**
+   * Modules to install.
+   *
+   * @var array
+   */
+  protected static $modules = ['entity_test', 'devel'];
+
+  /**
+   * {@inheritDoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->installEntitySchema('entity_test_rev');
+
+    $user = $this->createUser(permissions: ['access devel information'], values: ['name' => 'test']);
+
+    /** @var \Drupal\Core\Session\AccountProxyInterface $current_user */
+    $current_user = $this->container->get('current_user');
+    $current_user->setAccount($user);
+
+    // Create a field.
+    $this->createEntityReferenceField(
+      $this->entityType,
+      $this->bundle,
+      $this->fieldName,
+      'Field test',
+      $this->referencedEntityType,
+      'default',
+      ['target_bundles' => [$this->bundle]],
+      FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED
+    );
+  }
+
+  /**
+   * Test method.
+   */
+  public function testWithReferences(): void {
+    // Create the parent entity.
+    $entity = $this->container->get('entity_type.manager')
+      ->getStorage($this->entityType)
+      ->create(['type' => $this->bundle]);
+
+    // Create three target entities and attach them to parent field.
+    $target_entities = [];
+    $reference_field = [];
+    for ($i = 0; $i < 3; ++$i) {
+      $target_entity = $this->container->get('entity_type.manager')
+        ->getStorage($this->referencedEntityType)
+        ->create([
+          'type' => $this->bundle,
+          'name' => 'Related ' . $i,
+        ]);
+      $target_entity->save();
+      $target_entities[] = $target_entity;
+      $reference_field[]['target_id'] = $target_entity->id();
+    }
+
+    // Set the field value.
+    $entity->{$this->fieldName}->setValue($reference_field);
+    $entity->save();
+
+    /** @var \Drupal\devel\DevelDumperManagerInterface $dumper */
+    $dumper = $this->container->get('devel.dumper');
+    $result = $dumper->export($entity, NULL, 'drupal_variable', TRUE);
+    for ($i = 0; $i < 3; ++$i) {
+      $this->assertStringContainsString('Related ' . $i, (string) $result, 'The referenced entities are present in the dumper output.');
+    }
+  }
+
+}

modules/devel/tests/src/Kernel/DevelMailLogTest.php

@@ -0,0 +1,204 @@
+<?php
+
+namespace Drupal\Tests\devel\Kernel;
+
+use Drupal\Core\Mail\Plugin\Mail\TestMailCollector;
+use Drupal\devel\Plugin\Mail\DevelMailLog;
+use Drupal\KernelTests\KernelTestBase;
+
+/**
+ * Tests sending mails with debug interface.
+ *
+ * @group devel
+ */
+class DevelMailLogTest extends KernelTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var string[]
+   */
+  protected static $modules = ['devel', 'devel_test', 'system'];
+
+  /**
+   * The mail manager.
+   *
+   * @var \Drupal\Core\Mail\MailManagerInterface
+   */
+  protected $mailManager;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->installConfig(['system', 'devel']);
+
+    // Configure system.site mail settings.
+    $this->config('system.site')->set('mail', 'devel-test@example.com')->save();
+
+    $this->mailManager = $this->container->get('plugin.manager.mail');
+  }
+
+  /**
+   * Tests devel_mail_log plugin as default mail backend.
+   */
+  public function testDevelMailLogDefaultBackend(): void {
+    // Configure devel_mail_log as default mail backends.
+    $this->setDevelMailLogAsDefaultBackend();
+
+    // Ensures that devel_mail_log is the default mail plugin .
+    $mail_backend = $this->mailManager->getInstance(['module' => 'default', 'key' => 'default']);
+    $this->assertInstanceOf(DevelMailLog::class, $mail_backend);
+
+    $mail_backend = $this->mailManager->getInstance(['module' => 'somemodule', 'key' => 'default']);
+    $this->assertInstanceOf(DevelMailLog::class, $mail_backend);
+  }
+
+  /**
+   * Tests devel_mail_log plugin with multiple mail backend.
+   */
+  public function testDevelMailLogMultipleBackend(): void {
+    // Configure test_mail_collector as default mail backend.
+    $this->config('system.mail')
+      ->set('interface.default', 'test_mail_collector')
+      ->save();
+
+    // Configure devel_mail_log as a module-specific mail backend.
+    $this->config('system.mail')
+      ->set('interface.somemodule', 'devel_mail_log')
+      ->save();
+
+    // Ensures that devel_mail_log is not the default mail plugin.
+    $mail_backend = $this->mailManager->getInstance(['module' => 'default', 'key' => 'default']);
+    $this->assertInstanceOf(TestMailCollector::class, $mail_backend);
+
+    // Ensures that devel_mail_log is used as mail backend only for the
+    // specified module.
+    $mail_backend = $this->mailManager->getInstance(['module' => 'somemodule', 'key' => 'default']);
+    $this->assertInstanceOf(DevelMailLog::class, $mail_backend);
+  }
+
+  /**
+   * Tests devel_mail_log default settings.
+   */
+  public function testDevelMailDefaultSettings(): void {
+    $config = \Drupal::config('devel.settings');
+    $this->assertEquals('temporary://devel-mails', $config->get('debug_mail_directory'));
+    $this->assertEquals('%to-%subject-%datetime.mail.txt', $config->get('debug_mail_file_format'));
+  }
+
+  /**
+   * Tests devel mail log output.
+   */
+  public function testDevelMailLogOutput(): void {
+    $config = \Drupal::config('devel.settings');
+
+    /** @var \Drupal\Core\Language\LanguageManagerInterface $language_manager */
+    $language_manager = $this->container->get('language_manager');
+
+    // Parameters used for send the email.
+    $mail = [
+      'module' => 'devel_test',
+      'key' => 'devel_mail_log',
+      'to' => 'drupal@example.com',
+      'reply' => 'replyto@example.com',
+      'lang' => $language_manager->getCurrentLanguage()->getId(),
+    ];
+
+    // Parameters used for compose the email in devel_test module.
+    // @see devel_test_mail()
+    $params = [
+      'subject' => 'Devel mail log subject',
+      'body' => 'Devel mail log body',
+      'headers' => [
+        'from' => 'postmaster@example.com',
+        'additional' => [
+          'X-stupid' => 'dumb',
+        ],
+      ],
+    ];
+
+    // Configure devel_mail_log as default mail backends.
+    $this->setDevelMailLogAsDefaultBackend();
+
+    // Changes the default filename pattern removing the dynamic date
+    // placeholder for a more predictable filename output.
+    $random = $this->randomMachineName();
+    $filename_pattern = '%to-%subject-' . $random . '.mail.txt';
+    $this->config('devel.settings')
+      ->set('debug_mail_file_format', $filename_pattern)
+      ->save();
+
+    $expected_filename = 'drupal@example.com-Devel_mail_log_subject-' . $random . '.mail.txt';
+    $expected_output = <<<EOF
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8; format=flowed; delsp=yes
+Content-Transfer-Encoding: 8Bit
+X-Mailer: Drupal
+Return-Path: devel-test@example.com
+Sender: devel-test@example.com
+From: postmaster@example.com
+Reply-to: replyto@example.com
+X-stupid: dumb
+To: drupal@example.com
+Subject: Devel mail log subject
+
+Devel mail log body
+
+EOF;
+
+    // Ensures that the mail is captured by devel_mail_log and the placeholders
+    // in the filename are properly resolved.
+    $default_output_directory = $config->get('debug_mail_directory');
+    $expected_file_path = $default_output_directory . '/' . $expected_filename;
+
+    $this->mailManager->mail($mail['module'], $mail['key'], $mail['to'], $mail['lang'], $params, $mail['reply']);
+    $this->assertFileExists($expected_file_path);
+    $this->assertStringEqualsFile($expected_file_path, $expected_output);
+
+    // Ensures that even changing the default output directory devel_mail_log
+    // works as expected.
+    $changed_output_directory = 'temporary://my-folder';
+    $expected_file_path = $changed_output_directory . '/' . $expected_filename;
+    $this->config('devel.settings')
+      ->set('debug_mail_directory', $changed_output_directory)
+      ->save();
+
+    $result = $this->mailManager->mail($mail['module'], $mail['key'], $mail['to'], $mail['lang'], $params, $mail['reply']);
+    $this->assertTrue($result['result']);
+    $this->assertFileExists($expected_file_path);
+    $this->assertStringEqualsFile($expected_file_path, $expected_output);
+
+    // Ensures that if the default output directory is a public directory it
+    // will be protected by adding an .htaccess.
+    $public_output_directory = 'public://my-folder';
+    $expected_file_path = $public_output_directory . '/' . $expected_filename;
+    $this->config('devel.settings')
+      ->set('debug_mail_directory', $public_output_directory)
+      ->save();
+
+    $this->mailManager->mail($mail['module'], $mail['key'], $mail['to'], $mail['lang'], $params, $mail['reply']);
+    $this->assertFileExists($expected_file_path);
+    $this->assertStringEqualsFile($expected_file_path, $expected_output);
+    $this->assertFileExists($public_output_directory . '/.htaccess');
+  }
+
+  /**
+   * Configure devel_mail_log as default mail backend.
+   */
+  private function setDevelMailLogAsDefaultBackend(): void {
+    // @todo can this be avoided?
+    // KernelTestBase enforce the usage of 'test_mail_collector' plugin for
+    // collect the mails. Since we need to test devel mail plugin we manually
+    // configure the mail implementation to use 'devel_mail_log'.
+    $GLOBALS['config']['system.mail']['interface']['default'] = 'devel_mail_log';
+
+    // Configure devel_mail_log as default mail backend.
+    $this->config('system.mail')
+      ->set('interface.default', 'devel_mail_log')
+      ->save();
+  }
+
+}

modules/devel/tests/src/Kernel/DevelQueryDebugTest.php

@@ -0,0 +1,147 @@
+<?php
+
+namespace Drupal\Tests\devel\Kernel;
+
+use Drupal\Core\Messenger\MessengerTrait;
+use Drupal\KernelTests\KernelTestBase;
+use Drupal\user\Entity\Role;
+use Drupal\user\Entity\User;
+
+/**
+ * Tests query debug.
+ *
+ * @group devel
+ */
+class DevelQueryDebugTest extends KernelTestBase {
+
+  use MessengerTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['devel', 'system', 'user'];
+
+  /**
+   * The user used in test.
+   *
+   * @var \Drupal\user\UserInterface
+   */
+  protected $develUser;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->installSchema('system', 'sequences');
+    $this->installConfig(['system', 'devel']);
+    $this->installEntitySchema('user');
+
+    $devel_role = Role::create([
+      'id' => 'admin',
+      'label' => 'Admin',
+      'permissions' => ['access devel information'],
+    ]);
+    $devel_role->save();
+
+    $this->develUser = User::create([
+      'name' => $this->randomMachineName(),
+      'roles' => [$devel_role->id()],
+    ]);
+    $this->develUser->save();
+  }
+
+  /**
+   * Tests devel_query_debug_alter() for select queries.
+   */
+  public function testSelectQueryDebugTag(): void {
+    // Clear the messages stack.
+    $this->getDrupalMessages();
+
+    // Ensures that no debug message is shown to user without the adequate
+    // permissions.
+    $query = \Drupal::database()->select('users', 'u');
+    $query->fields('u', ['uid']);
+    $query->addTag('debug');
+    $query->execute();
+
+    $messages = $this->getDrupalMessages();
+    $this->assertEmpty($messages);
+
+    // Ensures that the SQL debug message is shown to user with the adequate
+    // permissions. We expect only one status message containing the SQL for
+    // the debugged query.
+    \Drupal::currentUser()->setAccount($this->develUser);
+    $expected_message = '
+SELECT u.uid AS uid\\n
+FROM\\n
+{users} u
+
+';
+
+    $query = \Drupal::database()->select('users', 'u');
+    $query->fields('u', ['uid']);
+    $query->addTag('debug');
+    $query->execute();
+
+    $messages = $this->getDrupalMessages();
+    $this->assertNotEmpty($messages['status']);
+    $this->assertCount(1, $messages['status']);
+    $actual_message = strip_tags($messages['status'][0]);
+    // In Drupal 9 the literals are quoted, but not in Drupal 8. We only need
+    // the actual content, so remove all quotes from the actual message found.
+    $actual_message = str_replace(['"', "'"], ['', ''], $actual_message);
+    $this->assertEquals($expected_message, $actual_message);
+  }
+
+  /**
+   * Tests devel_query_debug_alter() for entity queries.
+   */
+  public function testEntityQueryDebugTag(): void {
+    // Clear the messages stack.
+    $this->getDrupalMessages();
+
+    // Ensures that no debug message is shown to user without the adequate
+    // permissions.
+    $query = \Drupal::entityQuery('user')->accessCheck(FALSE);
+    $query->addTag('debug');
+    $query->execute();
+
+    $messages = $this->getDrupalMessages();
+    $this->assertEmpty($messages);
+
+    // Ensures that the SQL debug message is shown to user with the adequate
+    // permissions. We expect only one status message containing the SQL for
+    // the debugged entity query.
+    \Drupal::currentUser()->setAccount($this->develUser);
+    $expected_message = '
+SELECT base_table.uid AS uid, base_table.uid AS base_table_uid\\n
+FROM\\n
+{users} base_table
+
+';
+
+    $query = \Drupal::entityQuery('user')->accessCheck(FALSE);
+    $query->addTag('debug');
+    $query->execute();
+
+    $messages = $this->getDrupalMessages();
+    $this->assertNotEmpty($messages['status']);
+    $this->assertCount(1, $messages['status']);
+    $actual_message = strip_tags($messages['status'][0]);
+    $actual_message = str_replace(['"', "'"], ['', ''], $actual_message);
+    $this->assertEquals($expected_message, $actual_message);
+  }
+
+  /**
+   * Retrieves and removes the drupal messages.
+   *
+   * @return array
+   *   The messages
+   */
+  protected function getDrupalMessages() {
+    return $this->messenger()->deleteAll();
+  }
+
+}

modules/devel/tests/src/Kernel/DevelTwigExtensionTest.php

@@ -0,0 +1,203 @@
+<?php
+
+namespace Drupal\Tests\devel\Kernel;
+
+use Drupal\Core\DependencyInjection\ContainerBuilder;
+use Drupal\Core\Messenger\MessengerTrait;
+use Drupal\devel\Twig\Extension\Debug;
+use Drupal\KernelTests\KernelTestBase;
+use Drupal\user\Entity\Role;
+use Drupal\user\Entity\User;
+
+/**
+ * Tests Twig extensions.
+ *
+ * @group devel
+ */
+class DevelTwigExtensionTest extends KernelTestBase {
+
+  use DevelDumperTestTrait;
+  use MessengerTrait;
+
+  /**
+   * The user used in test.
+   *
+   * @var \Drupal\user\UserInterface
+   */
+  protected $develUser;
+
+  /**
+   * Modules to enable.
+   *
+   * @var string[]
+   */
+  protected static $modules = ['devel', 'user', 'system'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->installEntitySchema('user');
+    $this->installSchema('system', 'sequences');
+
+    $devel_role = Role::create([
+      'id' => 'admin',
+      'label' => 'Admin',
+      'permissions' => ['access devel information'],
+    ]);
+    $devel_role->save();
+
+    $this->develUser = User::create([
+      'name' => $this->randomMachineName(),
+      'roles' => [$devel_role->id()],
+    ]);
+    $this->develUser->save();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function register(ContainerBuilder $container): void {
+    parent::register($container);
+
+    $parameters = $container->getParameter('twig.config');
+    $parameters['debug'] = TRUE;
+    $container->setParameter('twig.config', $parameters);
+  }
+
+  /**
+   * Tests that Twig extension loads appropriately.
+   */
+  public function testTwigExtensionLoaded(): void {
+    $twig_service = \Drupal::service('twig');
+    $extension = $twig_service->getExtension(Debug::class);
+    $this->assertEquals($extension::class, Debug::class, 'Debug Extension loaded successfully.');
+  }
+
+  /**
+   * Tests that the Twig dump functions are registered properly.
+   */
+  public function testDumpFunctionsRegistered(): void {
+    /** @var \Drupal\Core\Template\TwigEnvironment $environment */
+    $environment = $this->container->get('twig');
+    $functions = $environment->getFunctions();
+
+    $dump_functions = ['devel_dump', 'kpr'];
+    $message_functions = ['devel_message', 'dpm', 'dsm'];
+    $registered_functions = $dump_functions + $message_functions;
+    foreach ($registered_functions as $name) {
+      $this->assertArrayHasKey($name, $functions);
+      $function = $functions[$name];
+      $this->assertEquals($function->getName(), $name);
+      $this->assertTrue($function->needsContext());
+      $this->assertTrue($function->needsEnvironment());
+      $this->assertTrue($function->isVariadic());
+
+      is_callable($function->getCallable(), TRUE, $callable);
+      if (in_array($name, $dump_functions)) {
+        $this->assertEquals($callable, Debug::class . '::dump');
+      }
+      else {
+        $this->assertEquals($callable, Debug::class . '::message');
+      }
+    }
+  }
+
+  /**
+   * Tests that the Twig function for XDebug integration is registered properly.
+   */
+  public function testXdebugIntegrationFunctionsRegistered(): void {
+    /** @var \Drupal\Core\Template\TwigEnvironment $environment */
+    $environment = $this->container->get('twig');
+    $function = $environment->getFunction('devel_breakpoint');
+    $this->assertNotNull($function);
+    $this->assertTrue($function->needsContext());
+    $this->assertTrue($function->needsEnvironment());
+    $this->assertTrue($function->isVariadic());
+    is_callable($function->getCallable(), TRUE, $callable);
+    $this->assertEquals($callable, Debug::class . '::breakpoint');
+  }
+
+  /**
+   * Tests that the Twig extension's dump functions produce the expected output.
+   */
+  public function testDumpFunctions(): void {
+    $template = 'test-with-context {{ twig_string }} {{ twig_array.first }} {{ twig_array.second }}{{ devel_dump() }}';
+    $expected_template_output = 'test-with-context context! first value second value';
+
+    $context = [
+      'twig_string' => 'context!',
+      'twig_array' => [
+        'first' => 'first value',
+        'second' => 'second value',
+      ],
+      'twig_object' => new \stdClass(),
+    ];
+
+    /** @var \Drupal\Core\Template\TwigEnvironment $environment */
+    $environment = \Drupal::service('twig');
+
+    // Ensures that the twig extension does nothing if the current
+    // user has not the adequate permission.
+    $this->assertTrue($environment->isDebug());
+    $this->assertEquals($environment->renderInline($template, $context), $expected_template_output);
+
+    \Drupal::currentUser()->setAccount($this->develUser);
+
+    // Ensures that if no argument is passed to the function the twig context is
+    // dumped.
+    $output = (string) $environment->renderInline($template, $context);
+    $this->assertStringContainsString($expected_template_output, $output, 'When no argument passed');
+    $this->assertContainsDump($output, $context, 'Twig context');
+
+    // Ensures that if an argument is passed to the function it is dumped.
+    $template = 'test-with-context {{ twig_string }} {{ twig_array.first }} {{ twig_array.second }}{{ devel_dump(twig_array) }}';
+    $output = (string) $environment->renderInline($template, $context);
+    $this->assertStringContainsString($expected_template_output, $output, 'When one argument is passed');
+    $this->assertContainsDump($output, $context['twig_array']);
+
+    // Ensures that if more than one argument is passed the function works
+    // properly and every argument is dumped separately.
+    $template = 'test-with-context {{ twig_string }} {{ twig_array.first }} {{ twig_array.second }}{{ devel_dump(twig_string, twig_array.first, twig_array, twig_object) }}';
+    $output = (string) $environment->renderInline($template, $context);
+    $this->assertStringContainsString($expected_template_output, $output, 'When multiple arguments are passed');
+    $this->assertContainsDump($output, $context['twig_string']);
+    $this->assertContainsDump($output, $context['twig_array']['first']);
+    $this->assertContainsDump($output, $context['twig_array']);
+    $this->assertContainsDump($output, $context['twig_object']);
+
+    // Clear messages.
+    $this->messenger()->deleteAll();
+
+    $retrieve_message = static fn($messages, $index): ?string => isset($messages['status'][$index]) ? (string) $messages['status'][$index] : NULL;
+
+    // Ensures that if no argument is passed to the function the twig context is
+    // dumped.
+    $template = 'test-with-context {{ twig_string }} {{ twig_array.first }} {{ twig_array.second }}{{ devel_message() }}';
+    $output = (string) $environment->renderInline($template, $context);
+    $this->assertStringContainsString($expected_template_output, $output, 'When no argument passed');
+    $messages = \Drupal::messenger()->deleteAll();
+    $this->assertDumpExportEquals($retrieve_message($messages, 0), $context, 'Twig context');
+
+    // Ensures that if an argument is passed to the function it is dumped.
+    $template = 'test-with-context {{ twig_string }} {{ twig_array.first }} {{ twig_array.second }}{{ devel_message(twig_array) }}';
+    $output = (string) $environment->renderInline($template, $context);
+    $this->assertStringContainsString($expected_template_output, $output, 'When one argument is passed');
+    $messages = $this->messenger()->deleteAll();
+    $this->assertDumpExportEquals($retrieve_message($messages, 0), $context['twig_array']);
+
+    // Ensures that if more than one argument is passed to the function works
+    // properly and every argument is dumped separately.
+    $template = 'test-with-context {{ twig_string }} {{ twig_array.first }} {{ twig_array.second }}{{ devel_message(twig_string, twig_array.first, twig_array, twig_object) }}';
+    $output = (string) $environment->renderInline($template, $context);
+    $this->assertStringContainsString($expected_template_output, $output, 'When multiple arguments are passed');
+    $messages = $this->messenger()->deleteAll();
+    $this->assertDumpExportEquals($retrieve_message($messages, 0), $context['twig_string']);
+    $this->assertDumpExportEquals($retrieve_message($messages, 1), $context['twig_array']['first']);
+    $this->assertDumpExportEquals($retrieve_message($messages, 2), $context['twig_array']);
+    $this->assertDumpExportEquals($retrieve_message($messages, 3), $context['twig_object']);
+  }
+
+}

modules/devel/tests/src/Unit/DevelClientSideFilterTableTest.php

@@ -0,0 +1,210 @@
+<?php
+
+namespace Drupal\Tests\devel\Unit;
+
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Drupal\devel\Element\ClientSideFilterTable;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * Tests ClientSideFilterTable element.
+ *
+ * @coversDefaultClass \Drupal\devel\Element\ClientSideFilterTable
+ * @group devel
+ */
+class DevelClientSideFilterTableTest extends UnitTestCase {
+
+  /**
+   * @covers ::getInfo
+   */
+  public function testGetInfo(): void {
+    $translation = $this->getStringTranslationStub();
+
+    $expected_info = [
+      '#filter_label' => $translation->translate('Search'),
+      '#filter_placeholder' => $translation->translate('Search'),
+      '#filter_description' => $translation->translate('Search'),
+      '#header' => [],
+      '#rows' => [],
+      '#empty' => '',
+      '#sticky' => FALSE,
+      '#responsive' => TRUE,
+      '#attributes' => [],
+      '#pre_render' => [
+        [ClientSideFilterTable::class, 'preRenderTable'],
+      ],
+    ];
+
+    $table = new ClientSideFilterTable([], 'test', 'test');
+    $table->setStringTranslation($translation);
+    $this->assertEquals($expected_info, $table->getInfo());
+  }
+
+  /**
+   * @covers ::preRenderTable
+   * @dataProvider providerPreRenderTable
+   */
+  public function testPreRenderTable($element, $expected): void {
+    $result = ClientSideFilterTable::preRenderTable($element);
+    $this->assertEquals($expected, $result);
+  }
+
+  /**
+   * Data provider for preRenderHtmlTag test.
+   */
+  public static function providerPreRenderTable(): array {
+    $data = [];
+    $filter_label = new TranslatableMarkup('Label 1');
+    $filter_label_2 = new TranslatableMarkup('Label 2');
+    $filter_placeholder = new TranslatableMarkup('Placeholder 1');
+    $filter_placeholder_2 = new TranslatableMarkup('Placeholder 2');
+    $filter_description = new TranslatableMarkup('Description 1');
+    $filter_description_2 = new TranslatableMarkup('Description 2');
+    $empty = new TranslatableMarkup('Empty');
+    $empty_2 = new TranslatableMarkup('Empty 2');
+    $actual = [
+      '#type' => 'devel_table_filter',
+      '#filter_label' => $filter_label,
+      '#filter_placeholder' => $filter_placeholder,
+      '#filter_description' => $filter_description,
+      '#header' => [],
+      '#rows' => [],
+      '#empty' => $empty,
+      '#responsive' => TRUE,
+      '#sticky' => TRUE,
+      '#attributes' => [
+        'class' => ['devel-a-list'],
+      ],
+    ];
+
+    $expected = [];
+    $expected['#attached']['library'][] = 'devel/devel-table-filter';
+    $expected['filters'] = [
+      '#type' => 'container',
+      '#weight' => -1,
+      '#attributes' => ['class' => ['table-filter', 'js-show']],
+      'name' => [
+        '#type' => 'search',
+        '#size' => 30,
+        '#title' => $filter_label,
+        '#placeholder' => $filter_placeholder,
+        '#attributes' => [
+          'class' => ['table-filter-text'],
+          'data-table' => ".js-devel-table-filter",
+          'autocomplete' => 'off',
+          'title' => $filter_description,
+        ],
+      ],
+    ];
+    $expected['table'] = [
+      '#type' => 'table',
+      '#header' => [],
+      '#rows' => [],
+      '#empty' => $empty,
+      '#responsive' => TRUE,
+      '#sticky' => TRUE,
+      '#attributes' => [
+        'class' => [
+          'devel-a-list',
+          'js-devel-table-filter',
+          'devel-table-filter',
+        ],
+      ],
+    ];
+
+    $data[] = [$actual, $expected];
+
+    $headers = ['Test1', 'Test2', 'Test3', 'Test4', 'Test5'];
+
+    $actual = [
+      '#type' => 'devel_table_filter',
+      '#filter_label' => $filter_label_2,
+      '#filter_placeholder' => $filter_placeholder_2,
+      '#filter_description' => $filter_description_2,
+      '#header' => $headers,
+      '#rows' => [
+        [
+          ['data' => 'test1', 'filter' => TRUE],
+          ['data' => 'test2', 'filter' => TRUE, 'class' => ['test2']],
+          ['data' => 'test3', 'class' => ['test3']],
+          ['test4'],
+          [
+            'data' => 'test5',
+            'filter' => TRUE,
+            'class' => ['devel-event-name-header'],
+            'colspan' => '3',
+            'header' => TRUE,
+          ],
+        ],
+      ],
+      '#empty' => $empty_2,
+      '#responsive' => FALSE,
+      '#sticky' => FALSE,
+      '#attributes' => [
+        'class' => ['devel-some-list'],
+      ],
+    ];
+
+    $expected = [];
+    $expected['#attached']['library'][] = 'devel/devel-table-filter';
+    $expected['filters'] = [
+      '#type' => 'container',
+      '#weight' => -1,
+      '#attributes' => ['class' => ['table-filter', 'js-show']],
+      'name' => [
+        '#type' => 'search',
+        '#size' => 30,
+        '#title' => $filter_label_2,
+        '#placeholder' => $filter_placeholder_2,
+        '#attributes' => [
+          'class' => ['table-filter-text'],
+          'data-table' => ".js-devel-table-filter--2",
+          'autocomplete' => 'off',
+          'title' => $filter_description_2,
+        ],
+      ],
+    ];
+    $expected['table'] = [
+      '#type' => 'table',
+      '#header' => $headers,
+      '#rows' => [
+        [
+          [
+            'data' => 'test1',
+            'filter' => TRUE,
+            'class' => ['table-filter-text-source'],
+          ],
+          [
+            'data' => 'test2',
+            'filter' => TRUE,
+            'class' => ['test2', 'table-filter-text-source'],
+          ],
+          ['data' => 'test3', 'class' => ['test3']],
+          ['test4'],
+          [
+            'data' => 'test5',
+            'filter' => TRUE,
+            'class' => ['devel-event-name-header', 'table-filter-text-source'],
+            'colspan' => '3',
+            'header' => TRUE,
+          ],
+        ],
+      ],
+      '#empty' => $empty_2,
+      '#responsive' => FALSE,
+      '#sticky' => FALSE,
+      '#attributes' => [
+        'class' => [
+          'devel-some-list',
+          'js-devel-table-filter--2',
+          'devel-table-filter',
+        ],
+      ],
+    ];
+
+    $data[] = [$actual, $expected];
+
+    return $data;
+  }
+
+}