diff --git a/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
index e19169f..f3841f6 100644
--- a/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
@@ -1066,28 +1066,8 @@ private function prepareEnvironment() {
     drupal_static_reset();
 
     // Reset and create a new service container.
-    $this->container = new ContainerBuilder();
-
-    // @todo Remove this once this class has no calls to t() and format_plural()
-    $this->container->setParameter('language.default_values', Language::$defaultValues);
-    $this->container->register('language.default', 'Drupal\Core\Language\LanguageDefault')
-      ->addArgument('%language.default_values%');
-    $this->container->register('language_manager', 'Drupal\Core\Language\LanguageManager')
-      ->addArgument(new Reference('language.default'));
-    $this->container->register('string_translation', 'Drupal\Core\StringTranslation\TranslationManager')
-      ->addArgument(new Reference('language_manager'));
-
-    // Register info parser.
-    $this->container->register('info_parser', 'Drupal\Core\Extension\InfoParser');
-
-    $request = Request::create('/');
-    $this->container->set('request', $request);
-
-    // Run all tests as a anonymous user by default, web tests will replace that
-    // during the test set up.
-    $this->container->set('current_user', new AnonymousUserSession());
-
-    \Drupal::setContainer($this->container);
+    $this->container = NULL;
+    \Drupal::setContainer(NULL);
 
     // Unset globals.
     unset($GLOBALS['config_directories']);
diff --git a/core/modules/system/lib/Drupal/system/Tests/Common/SizeUnitTest.php b/core/modules/system/lib/Drupal/system/Tests/Common/SizeUnitTest.php
index a8a2662..1a92d70 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Common/SizeUnitTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Common/SizeUnitTest.php
@@ -7,12 +7,12 @@
 
 namespace Drupal\system\Tests\Common;
 
-use Drupal\simpletest\UnitTestBase;
+use Drupal\simpletest\DrupalUnitTestBase;
 
 /**
  * Tests file size parsing and formatting functions.
  */
-class SizeUnitTest extends UnitTestBase {
+class SizeUnitTest extends DrupalUnitTestBase {
   protected $exact_test_cases;
   protected $rounded_test_cases;
 
@@ -25,6 +25,7 @@ public static function getInfo() {
   }
 
   function setUp() {
+    parent::setUp();
     $kb = DRUPAL_KILOBYTE;
     $this->exact_test_cases = array(
       '1 byte' => 1,
@@ -44,7 +45,6 @@ function setUp() {
       round(67234178751368124 / ($this->exact_test_cases['1 PB']), 2) . ' PB' => 67234178751368124, // petabytes
       round(235346823821125814962843827 / ($this->exact_test_cases['1 YB']), 2) . ' YB' => 235346823821125814962843827, // yottabytes
     );
-    parent::setUp();
   }
 
   /**
diff --git a/core/modules/system/lib/Drupal/system/Tests/Plugin/PluginTestBase.php b/core/modules/system/lib/Drupal/system/Tests/Plugin/PluginTestBase.php
index 50d5736..0ba4e13 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Plugin/PluginTestBase.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Plugin/PluginTestBase.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\system\Tests\Plugin;
 
-use Drupal\simpletest\UnitTestBase;
+use Drupal\simpletest\DrupalUnitTestBase;
 use Drupal\plugin_test\Plugin\TestPluginManager;
 use Drupal\plugin_test\Plugin\MockBlockManager;
 use Drupal\plugin_test\Plugin\DefaultsTestPluginManager;
@@ -16,7 +16,15 @@
 /**
  * Base class for Plugin API unit tests.
  */
-abstract class PluginTestBase extends UnitTestBase {
+abstract class PluginTestBase extends DrupalUnitTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  public static $modules = array('plugin_test');
+
   protected $testPluginManager;
   protected $testPluginExpectedDefinitions;
   protected $mockBlockManager;