Issue #3087879 by andypost, jhodgdon, alexpott: Use admin theme annotation for help topics search

core/modules/help_topics/src/Plugin/Search/HelpSearch.php

@@ -33,7 +33,8 @@
  *
  * @SearchPlugin(
  *   id = "help_search",
- *   title = @Translation("Help")
+ *   title = @Translation("Help"),
+ *   use_admin_theme = TRUE,
  * )
  *
  * @internal

core/modules/help_topics/tests/src/Kernel/HelpSearchPluginTest.php

+<?php
+
+namespace Drupal\Tests\help_topics\Kernel;
+
+use Drupal\Core\Access\AccessibleInterface;
+use Drupal\KernelTests\KernelTestBase;
+use Drupal\search\Plugin\SearchIndexingInterface;
+
+/**
+ * Tests search plugin behaviors.
+ *
+ * @group help_topics
+ *
+ * @see \Drupal\help_topics\Plugin\Search\HelpSearch
+ */
+class HelpSearchPluginTest extends KernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['help', 'help_topics', 'search'];
+
+  /**
+   * Tests search plugin annotation and interfaces.
+   */
+  public function testAnnotation() {
+    /** @var \Drupal\search\SearchPluginManager $manager */
+    $manager = \Drupal::service('plugin.manager.search');
+    /** @var \Drupal\help_topics\Plugin\Search\HelpSearch $plugin */
+    $plugin = $manager->createInstance('help_search');
+    $this->assertInstanceOf(AccessibleInterface::class, $plugin);
+    $this->assertInstanceOf(SearchIndexingInterface::class, $plugin);
+    $this->assertSame('Help', (string) $plugin->getPluginDefinition()['title']);
+    $this->assertTrue($plugin->usesAdminTheme());
+  }
+
+}