ENGCOM-6106: #24781: Elasticsearch 6 works with Elasticsearch 5 client on frontend #24974

 - Merge Pull Request #24974 from p-bystritsky/magento2:ISSUE-24781
 - Merged commits:
   1. e18a6fb
   2. 0de03aa
   3. 74e1278

Author: magento-engcom-team

app/code/Magento/Elasticsearch/etc/di.xml

@@ -267,7 +267,7 @@
     </type>
     <virtualType name="Magento\Elasticsearch\Elasticsearch5\SearchAdapter\ConnectionManager" type="Magento\Elasticsearch\SearchAdapter\ConnectionManager">
         <arguments>
-            <argument name="clientFactory" xsi:type="object">Magento\Elasticsearch\Elasticsearch5\Model\Client\ElasticsearchFactory</argument>
+            <argument name="clientFactory" xsi:type="object">Magento\Elasticsearch\Elasticsearch5\Model\Client\ClientFactoryProxy</argument>
             <argument name="clientConfig" xsi:type="object">Magento\Elasticsearch\Model\Config</argument>
         </arguments>
     </virtualType>

dev/tests/integration/testsuite/Magento/Elasticsearch6/SearchAdapter/ConnectionManagerTest.php

@@ -0,0 +1,64 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+declare(strict_types=1);
+
+namespace Magento\Elasticsearch6\SearchAdapter;
+
+use Magento\Elasticsearch\Elasticsearch5\SearchAdapter\ConnectionManager;
+use Magento\TestFramework\Helper\Bootstrap;
+
+/**
+ * Test for \Magento\Elasticsearch\SearchAdapter\ConnectionManager class.
+ */
+class ConnectionManagerTest extends \PHPUnit\Framework\TestCase
+{
+    /**
+     * @var \Magento\Framework\ObjectManagerInterface
+     */
+    private $objectManager;
+
+    /**
+     * @var \Magento\Elasticsearch\SearchAdapter\ConnectionManager
+     */
+    private $connectionManager;
+
+    protected function setUp()
+    {
+        $this->objectManager = Bootstrap::getObjectManager();
+
+        $this->connectionManager = $this->objectManager->create(ConnectionManager::class);
+    }
+
+    /**
+     * Test if 'elasticsearch5' search engine returned by connection manager.
+     *
+     * @magentoAppIsolation enabled
+     * @magentoConfigFixture default/catalog/search/engine elasticsearch5
+     */
+    public function testCorrectElasticsearchClientEs5()
+    {
+        $connection = $this->connectionManager->getConnection();
+        $this->assertInstanceOf(
+            \Magento\Elasticsearch\Elasticsearch5\Model\Client\Elasticsearch::class,
+            $connection
+        );
+    }
+
+    /**
+     * Test if 'elasticsearch6' search engine returned by connection manager.
+     *
+     * @magentoAppIsolation enabled
+     * @magentoConfigFixture default/catalog/search/engine elasticsearch6
+     */
+    public function testCorrectElasticsearchClientEs6()
+    {
+        $connection = $this->connectionManager->getConnection();
+        $this->assertInstanceOf(
+            \Magento\Elasticsearch6\Model\Client\Elasticsearch::class,
+            $connection
+        );
+    }
+}