diff --git a/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
index a064d01..8a55c25 100644
--- a/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
@@ -178,6 +178,13 @@
   protected $curlCookies = array();
 
   /**
+   * An array of custom translations suitable for drupal_rewrite_settings().
+   *
+   * @var array
+   */
+  protected $customTranslations;
+
+  /**
    * Constructor for \Drupal\simpletest\WebTestBase.
    */
   function __construct($test_id = NULL) {
@@ -918,6 +925,41 @@ protected function writeSettings($settings) {
   }
 
   /**
+   * Adds custom translations.
+   *
+   * @param string $langcode
+   *   The langcode to add translations for.
+   * @param array $values
+   *   Array of values containing the untranslated string and its translation.
+   *   For example:
+   *   @code
+   *   array(
+   *     '' => array('Sunday' => 'domingo'),
+   *     'Long month name' => array('March' => 'marzo'),
+   *   );
+   *   @endcode
+   */
+  protected function addCustomTranslations($langcode, array $values) {
+    $this->settingsSet('locale_custom_strings_' . $langcode, $values);
+    foreach ($values as $key => $translations) {
+      foreach ($translations as $label => $value) {
+        $this->customTranslations['locale_custom_strings_' . $langcode][$key][$label] = (object) array(
+          'value' => $value,
+          'required' => TRUE,
+        );
+      }
+    }
+  }
+
+  /**
+   * Writes custom translations to test site's settings.php.
+   */
+  protected function writeCustomTranslations() {
+    $this->writeSettings(array('settings' => $this->customTranslations));
+    $this->customTranslations = array();
+  }
+
+  /**
    * Overrides \Drupal\simpletest\TestBase::rebuildContainer().
    */
   protected function rebuildContainer() {
diff --git a/core/modules/system/lib/Drupal/system/Tests/Menu/MenuRouterTest.php b/core/modules/system/lib/Drupal/system/Tests/Menu/MenuRouterTest.php
index 8c41c4d..f341681 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Menu/MenuRouterTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Menu/MenuRouterTest.php
@@ -7,12 +7,12 @@
 
 namespace Drupal\system\Tests\Menu;
 
-use Drupal\system\Tests\System\CustomStringsTestBase;
+use Drupal\simpletest\WebTestBase;
 
 /**
  * Tests menu router and hook_menu() functionality.
  */
-class MenuRouterTest extends CustomStringsTestBase {
+class MenuRouterTest extends WebTestBase {
 
   /**
    * Modules to enable.
diff --git a/core/modules/system/lib/Drupal/system/Tests/Plugin/CacheDecoratorLanguageTest.php b/core/modules/system/lib/Drupal/system/Tests/Plugin/CacheDecoratorLanguageTest.php
index 4e1dadf..34e3889 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Plugin/CacheDecoratorLanguageTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Plugin/CacheDecoratorLanguageTest.php
@@ -9,12 +9,12 @@
 
 use Drupal\Core\Language\Language;
 use Drupal\plugin_test\Plugin\CachedMockBlockManager;
-use Drupal\system\Tests\System\CustomStringsTestBase;
+use Drupal\simpletest\WebTestBase;
 
 /**
  * Tests that the AlterDecorator fires and respects the alter hook.
  */
-class CacheDecoratorLanguageTest extends CustomStringsTestBase {
+class CacheDecoratorLanguageTest extends WebTestBase {
 
   /**
    * Modules to enable.
diff --git a/core/modules/system/lib/Drupal/system/Tests/System/CustomStringsTestBase.php b/core/modules/system/lib/Drupal/system/Tests/System/CustomStringsTestBase.php
deleted file mode 100644
index 1a56c9e..0000000
--- a/core/modules/system/lib/Drupal/system/Tests/System/CustomStringsTestBase.php
+++ /dev/null
@@ -1,59 +0,0 @@
-<?php
-
-/**
- * @file
- * Contains \Drupal\system\Tests\System\CustomStringsTestBase.
- */
-
-namespace Drupal\system\Tests\System;
-
-use Drupal\simpletest\WebTestBase;
-
-/**
- * Defines a base class for testing custom string translations functionality.
- */
-abstract class CustomStringsTestBase extends WebTestBase {
-
-  /**
-   * An array of custom translations suitable for drupal_rewrite_settings().
-   *
-   * @var array
-   */
-  protected $customTranslations;
-
-  /**
-   * Adds custom translations.
-   *
-   * @param string $langcode
-   *   The langcode to add translations for.
-   * @param array $values
-   *   Array of values containing the untranslated string and its translation.
-   *   For example:
-   *   @code
-   *   array(
-   *     '' => array('Sunday' => 'domingo'),
-   *     'Long month name' => array('March' => 'marzo'),
-   *   );
-   *   @endcode
-   */
-  protected function addCustomTranslations($langcode, array $values) {
-    $this->settingsSet('locale_custom_strings_' . $langcode, $values);
-    foreach ($values as $key => $translations) {
-      foreach ($translations as $label => $value) {
-        $this->customTranslations['locale_custom_strings_' . $langcode][$key][$label] = (object) array(
-          'value' => $value,
-          'required' => TRUE,
-        );
-      }
-    }
-  }
-
-  /**
-   * Writes custom translations to test site's settings.php.
-   */
-  protected function writeCustomTranslations() {
-    $this->writeSettings(array('settings' => $this->customTranslations));
-    $this->customTranslations = array();
-  }
-
-}