Add integration test to ensure correct unique varchar indexes

[MAILPOET-4832]

mailpoet/tests/integration/Migrations/DbIndexesTest.php

@@ -0,0 +1,36 @@
+<?php declare(strict_types = 1);
+
+namespace MailPoet\Test\Config;
+
+use MailPoet\Config\Env;
+use MailPoetVendor\Doctrine\DBAL\Connection;
+
+class DbIndexesTest extends \MailPoetTest {
+  /**
+   * This test checks that we don't have an unique varchar index on a varchar column with a length bigger than 191.
+   * The length of 191 is the safe limit that works for all common MySQL configurations.
+   * We don't want to allow creating unique indexes on varchar columns with a length bigger than 191.
+   * @see https://stackoverflow.com/questions/15157227/mysql-varchar-index-length/16474039#16474039
+   */
+  public function testDbHasCorrectUniqueVarcharIndexes() {
+    $connection = $this->diContainer->get(Connection::class);
+    $incorrectIndexes = $connection->executeQuery("SELECT DISTINCT
+      ISS.TABLE_NAME,
+      ISS.INDEX_NAME,
+      ISS.COLUMN_NAME,
+      ISS.NON_UNIQUE,
+      ISC.CHARACTER_MAXIMUM_LENGTH,
+      ISC.DATA_TYPE
+    FROM INFORMATION_SCHEMA.STATISTICS ISS
+    JOIN INFORMATION_SCHEMA.COLUMNS ISC ON ISC.COLUMN_NAME = ISS.COLUMN_NAME AND ISC.TABLE_NAME = ISS.TABLE_NAME
+    WHERE ISS.TABLE_NAME LIKE :prefix
+      AND ISS.NON_UNIQUE = 0
+      AND ISC.DATA_TYPE = 'varchar'
+      AND ISC.CHARACTER_MAXIMUM_LENGTH > 191;",
+      ['prefix' => Env::$dbPrefix . '%']
+    )->fetchAllAssociative();
+    if (!empty($incorrectIndexes)) {
+      $this->fail("The following unique indexes use varchar column, but have incorrect length over 191 chars:\n " . json_encode($incorrectIndexes, JSON_PRETTY_PRINT));
+    }
+  }
+}