diff -u b/core/modules/system/lib/Drupal/system/Tests/KeyValueStore/StorageTestBase.php b/core/modules/system/lib/Drupal/system/Tests/KeyValueStore/StorageTestBase.php
--- b/core/modules/system/lib/Drupal/system/Tests/KeyValueStore/StorageTestBase.php
+++ b/core/modules/system/lib/Drupal/system/Tests/KeyValueStore/StorageTestBase.php
@@ -61,7 +61,8 @@
       ->addArgument(new Reference('settings'));
     $this->container
       ->register('keyvalue.expirable', 'Drupal\Core\KeyValueStore\KeyValueExpirableFactory')
-      ->addArgument(new Reference('service_container'));
+      ->addArgument(new Reference('service_container'))
+      ->addArgument(new Reference('settings'));
     // Define two data collections,
     $this->collections = array(0 => 'zero', 1 => 'one');
 
only in patch2:
unchanged:
--- a/core/modules/system/lib/Drupal/system/Tests/KeyValueStore/DatabaseStorageExpirableTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/KeyValueStore/DatabaseStorageExpirableTest.php
@@ -36,8 +36,7 @@ protected function setUp() {
     $this->container
       ->register('keyvalue.expirable.database', 'Drupal\Core\KeyValueStore\KeyValueDatabaseExpirableFactory')
       ->addArgument(new Reference('database'));
-    global $conf;
-    $conf['keyvalue_expirable_default'] = 'keyvalue.expirable.database';
+    $this->settingsSet('keyvalue_expirable_default', 'keyvalue.expirable.database');
   }
 
   protected function tearDown() {
only in patch2:
unchanged:
--- a/core/modules/system/lib/Drupal/system/Tests/KeyValueStore/MemoryStorageTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/KeyValueStore/MemoryStorageTest.php
@@ -31,22 +31,10 @@ protected function setUp() {
     parent::setUp();
     $this->container
       ->register('keyvalue.memory', 'Drupal\Core\KeyValueStore\KeyValueMemoryFactory');
-    global $conf;
     if (isset($conf['keyvalue_default'])) {
       $this->originalKeyValue = $conf['keyvalue_default'];
     }
-    $conf['keyvalue_default'] = 'keyvalue.memory';
-  }
-
-  protected function tearDown() {
-    global $conf;
-    if (isset($this->originalKeyValue)) {
-      $conf['keyvalue_default'] = $this->originalKeyValue;
-    }
-    else {
-      unset($conf['keyvalue_default']);
-    }
-    parent::tearDown();
+    $this->settingsSet('keyvalue_default', 'keyvalue.memory');
   }
 
 }