only in patch2:
unchanged:
--- a/core/modules/system/lib/Drupal/system/Tests/Common/SizeUnitTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Common/SizeUnitTest.php
@@ -7,7 +7,9 @@
 
 namespace Drupal\system\Tests\Common;
 
+use Drupal\Core\Language\Language;
 use Drupal\simpletest\UnitTestBase;
+use Symfony\Component\DependencyInjection\Reference;
 
 /**
  * Tests file size parsing and formatting functions.
@@ -25,6 +27,16 @@ public static function getInfo() {
   }
 
   function setUp() {
+    // The function format_size uses the function format_plural() which depends
+    // on the translation service.
+    $this->container->setParameter('language.default_values', Language::$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'));
+
     $kb = DRUPAL_KILOBYTE;
     $this->exact_test_cases = array(
       '1 byte' => 1,
only in patch2:
unchanged:
--- a/core/modules/system/lib/Drupal/system/Tests/Plugin/Discovery/AnnotatedClassDiscoveryTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Plugin/Discovery/AnnotatedClassDiscoveryTest.php
@@ -24,6 +24,7 @@ public static function getInfo() {
 
   public function setUp() {
     parent::setUp();
+    $this->setUpTranslationServices();
     $this->expectedDefinitions = array(
       'apple' => array(
         'id' => 'apple',
@@ -37,7 +38,7 @@ public function setUp() {
         'label' => 'Banana',
         'color' => 'yellow',
         'uses' => array(
-          'bread' => t('Banana bread'),
+          'bread' => $this->container->get('string_translation')->translate('Banana bread'),
         ),
         'class' => 'Drupal\plugin_test\Plugin\plugin_test\fruit\Banana',
         'provider' => 'plugin_test',
only in patch2:
unchanged:
--- a/core/modules/system/lib/Drupal/system/Tests/Plugin/Discovery/CustomDirectoryAnnotatedClassDiscoveryTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Plugin/Discovery/CustomDirectoryAnnotatedClassDiscoveryTest.php
@@ -24,7 +24,7 @@ public static function getInfo() {
 
   protected function setUp() {
     parent::setUp();
-
+    $this->setUpTranslationServices();
     $this->expectedDefinitions = array(
       'custom_example_1' => array(
         'id' => 'custom_example_1',
@@ -50,7 +50,7 @@ protected function setUp() {
         'label' => 'Banana',
         'color' => 'yellow',
         'uses' => array(
-          'bread' => t('Banana bread'),
+          'bread' => $this->container->get('string_translation')->translate('Banana bread'),
         ),
         'class' => 'Drupal\plugin_test\Plugin\plugin_test\fruit\Banana',
         'provider' => 'plugin_test',
only in patch2:
unchanged:
--- a/core/modules/system/lib/Drupal/system/Tests/Plugin/Discovery/DiscoveryTestBase.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Plugin/Discovery/DiscoveryTestBase.php
@@ -7,7 +7,9 @@
 
 namespace Drupal\system\Tests\Plugin\Discovery;
 
+use Drupal\Core\Language\Language;
 use Drupal\simpletest\UnitTestBase;
+use Symfony\Component\DependencyInjection\Reference;
 
 /**
  * Tests that plugins are correctly discovered.
@@ -58,5 +60,20 @@ function testDiscoveryInterface() {
     // Ensure that NULL is returned as the definition of a non-existing plugin.
     $this->assertIdentical($this->emptyDiscovery->getDefinition('non_existing'), NULL, 'NULL returned as the definition of a non-existing plugin.');
   }
+
+  /**
+   * Create translation services.
+   *
+   * Use this if the annotation under test uses @Translation.
+   */
+  protected function setUpTranslationServices() {
+    $this->container->setParameter('language.default_values', Language::$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'));
+  }
 }
 
only in patch2:
unchanged:
--- a/core/modules/system/lib/Drupal/system/Tests/Plugin/PluginTestBase.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Plugin/PluginTestBase.php
@@ -7,10 +7,12 @@
 
 namespace Drupal\system\Tests\Plugin;
 
+use Drupal\Core\Language\Language;
 use Drupal\simpletest\UnitTestBase;
 use Drupal\plugin_test\Plugin\TestPluginManager;
 use Drupal\plugin_test\Plugin\MockBlockManager;
 use Drupal\plugin_test\Plugin\DefaultsTestPluginManager;
+use Symfony\Component\DependencyInjection\Reference;
 
 /**
  * Base class for Plugin API unit tests.
@@ -26,6 +28,16 @@
   public function setUp() {
     parent::setUp();
 
+    // Annotations require the translation service so that @Translation will
+    // work.
+    $this->container->setParameter('language.default_values', Language::$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'));
+
     // Real modules implementing plugin types may expose a module-specific API
     // for retrieving each type's plugin manager, or make them available in
     // Drupal's dependency injection container, but for unit testing, we get