diff --git a/core/core.services.yml b/core/core.services.yml
index 5997021..0b18c3b 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -736,6 +736,7 @@ services:
     arguments: ['%language.default_values%']
   string_translator.custom_strings:
     class: Drupal\Core\StringTranslation\Translator\CustomStrings
+    arguments: ['@settings']
     tags:
       - { name: string_translator, priority: 30 }
   string_translation:
diff --git a/core/lib/Drupal/Core/StringTranslation/Translator/CustomStrings.php b/core/lib/Drupal/Core/StringTranslation/Translator/CustomStrings.php
index 0fbf9bf..8e733d5 100644
--- a/core/lib/Drupal/Core/StringTranslation/Translator/CustomStrings.php
+++ b/core/lib/Drupal/Core/StringTranslation/Translator/CustomStrings.php
@@ -3,6 +3,7 @@
 namespace Drupal\Core\StringTranslation\Translator;
 
 use Drupal\Core\Site\Settings;
+use Drupal\Core\DependencyInjection\DependencySerializationTrait;
 
 /**
  * String translator using overrides from variables.
@@ -12,11 +13,31 @@
  */
 class CustomStrings extends StaticTranslation {
 
+  use DependencySerializationTrait;
+
+  /**
+   * The settings read only object.
+   *
+   * @var \Drupal\Core\Site\Settings
+   */
+  protected $settings;
+
+  /**
+   * Constructs a CustomStrings object.
+   *
+   * @param \Drupal\Core\Site\Settings $settings
+   *   The settings read only object.
+   */
+  public function __construct(Settings $settings) {
+    parent::__construct();
+    $this->settings = $settings;
+  }
+
   /**
    * {@inheritdoc}
    */
   protected function getLanguage($langcode) {
-    return Settings::get('locale_custom_strings_' . $langcode, array());
+    return $this->settings->get('locale_custom_strings_' . $langcode, array());
   }
 
 }
diff --git a/core/modules/datetime/src/Tests/DateTimeFormInjectionTest.php b/core/modules/datetime/tests/src/Kernel/DateTimeFormInjectionTest.php
similarity index 84%
rename from core/modules/datetime/src/Tests/DateTimeFormInjectionTest.php
rename to core/modules/datetime/tests/src/Kernel/DateTimeFormInjectionTest.php
index 150c909..a65d439 100644
--- a/core/modules/datetime/src/Tests/DateTimeFormInjectionTest.php
+++ b/core/modules/datetime/tests/src/Kernel/DateTimeFormInjectionTest.php
@@ -1,19 +1,13 @@
 <?php
-/**
- * @file
- * Contains \Drupal\datetime\Tests\DateTimeFormInjectionTest
- */
-
-namespace Drupal\datetime\Tests;
 
+namespace Drupal\Tests\datetime\Kernel;
 
 use Drupal\Core\Datetime\DrupalDateTime;
 use Drupal\Core\DependencyInjection\DependencySerializationTrait;
 use Drupal\Core\Form\FormInterface;
 use Drupal\Core\Form\FormState;
 use Drupal\Core\Form\FormStateInterface;
-use Drupal\simpletest\KernelTestBase;
-use Drupal\user\Entity\User;
+use Drupal\KernelTests\KernelTestBase;
 
 /**
  * Tests serializing a form with an injected datetime instance.
@@ -36,7 +30,15 @@ class DateTimeFormInjectionTest extends KernelTestBase implements FormInterface
    *
    * @var array
    */
-  public static $modules = array('system', 'datetime');
+  public static $modules = ['system', 'datetime'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+    $this->installSchema('system', ['key_value_expire', 'sequences']);
+  }
 
   /**
    * {@inheritdoc}
@@ -49,7 +51,7 @@ public function getFormId() {
    * Process callback.
    *
    * @param array $element
-   *   Form element
+   *   Form element.
    *
    * @return array
    *   Processed element.
@@ -62,21 +64,21 @@ public function process($element) {
    * {@inheritdoc}
    */
   public function buildForm(array $form, FormStateInterface $form_state) {
-    $form['datelist_element'] = array(
+    $form['datelist_element'] = [
       '#title' => 'datelist test',
       '#type' => 'datelist',
       '#default_value' => new DrupalDateTime('2000-01-01 00:00:00'),
-      '#date_part_order' => array(
+      '#date_part_order' => [
         'month',
         'day',
         'year',
         'hour',
         'minute', 'ampm',
-      ),
-      '#date_text_parts' => array('year'),
+      ],
+      '#date_text_parts' => ['year'],
       '#date_year_range' => '2010:2020',
       '#date_increment' => 15,
-    );
+    ];
     $form['#process'][] = [$this, 'process'];
     return $form;
   }
@@ -95,15 +97,7 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
   }
 
   /**
-   * {@inheritdoc}
-   */
-  protected function setUp() {
-    parent::setUp();
-    $this->installSchema('system', ['key_value_expire', 'sequences']);
-  }
-
-  /**
-   * Tests db log injection serialization.
+   * Tests custom string injection serialization.
    */
   public function testDatetimeSerialization() {
     $form_state = new FormState();