Issue #3209453 by daffie: The service "search.index" should be backend_overridable

core/modules/search/search.services.yml

@@ -10,6 +10,8 @@ services:
   search.index:
     class: Drupal\search\SearchIndex
     arguments: ['@config.factory', '@database','@database.replica', '@cache_tags.invalidator', '@search.text_processor']
+    tags:
+      - { name: backend_overridable }
 
   search.text_processor:
     class: Drupal\search\SearchTextProcessor

core/modules/search/tests/src/Kernel/SearchIndexTest.php

+<?php
+
+namespace Drupal\Tests\search\Kernel;
+
+use Drupal\KernelTests\KernelTestBase;
+
+/**
+ * Tests the service "search.index".
+ *
+ * @group search
+ */
+class SearchIndexTest extends KernelTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  protected static $modules = ['search'];
+
+  /**
+   * Test that the service "search.index" is backend overridable.
+   */
+  public function testSearchIndexServiceIsBackendOverridable() {
+    $definition = $this->container->getDefinition('search.index');
+    $this->assertTrue($definition->hasTag('backend_overridable'));
+  }
+
+}