diff --git a/core/modules/system/lib/Drupal/system/Tests/Cache/GenericBackendUnitTestBase.php b/core/modules/system/lib/Drupal/system/Tests/Cache/GenericBackendUnitTestBase.php
index ae59f01..56d9ba7 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Cache/GenericBackendUnitTestBase.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Cache/GenericBackendUnitTestBase.php
@@ -9,7 +9,8 @@ namespace Drupal\system\Tests\Cache;
 
 use Drupal\Core\Cache\CacheBackendInterface;
 use Drupal\simpletest\UnitTestBase;
-use stdClass;
+
+use \stdClass;
 
 /**
  * Full generic unit test suite for any cache backend. In order to use it for a
@@ -184,7 +185,6 @@ abstract class GenericBackendUnitTestBase extends UnitTestBase {
       'test3' => '',
       'test4' => 12.64,
       'test5' => false,
-      'test6' => array(1,2,3),
     );
 
     // Create cache entries.
@@ -193,11 +193,10 @@ abstract class GenericBackendUnitTestBase extends UnitTestBase {
     }
 
     // Retrieve and test cache objects.
-    foreach ($variables as $cid => $data) {
+    foreach ($variables as $cid => $value) {
       $object = $backend->get($cid);
-      $this->assert(is_object($object), format_string("Backend returned an object for cache id %cid.", array('%cid' => $cid)));
-      // Ensure that variable type has been persisted.
-      $this->assertIdentical($data, $object->data);
+      $this->assert(is_object($object), sprintf("Backend returned an object for cache id %s.", $cid));
+      $this->assertIdentical($value, $object->data, sprintf("Data of cached id %s kept is identical in type and value", $cid));
     }
   }
 
@@ -228,78 +227,52 @@ abstract class GenericBackendUnitTestBase extends UnitTestBase {
 
     $cids = $reference;
     $ret = $backend->getMultiple($cids);
-
-    // Cids that should be keys $ret array and not in $cid array.
-    $returned_cids = array(
-      'test2',
-      'test3',
-      'test6',
-      'test7',
-    );
-    // Cids that should in $cid array and not keys $ret array.
-    $missing_cids = array(
-      'test19',
-      'test21',
-    );
-
-    foreach ($returned_cids as $cid) {
-      // Should be a key in $ret.
-      $this->assert(isset($ret[$cid]), format_string("Existing cache id %cid is set in return from getMultiple().", array('%cid' => $cid)));
-      // Should not be a value in $cids.
-      $this->assertFalse(in_array($cid, $cids), format_string("Existing cache id %cid is not a value in array passed to getMultiple().", array('%cid' => $cid)));
-    }
-    foreach ($missing_cids as $cid) {
-      // Should be a not be key in $ret.
-      $this->assertFalse(isset($ret[$cid]), format_string("Non existing cache id %cid is not set.", array('%cid' => $cid)));
-      // Should be a value in $cids.
-      $this->assertTrue(in_array($cid, $cids), format_string("Non existing cache id %cid is a value in array passed to getMultiple().", array('%cid' => $cid)));
-    }
-
-    // Test return array values.
-    $this->assertIdentical($ret['test2']->data, 3, "Existing cache id test2 has the correct value.");
-    $this->assertIdentical($ret['test3']->data, 5, "Existing cache id test3 has the correct value.");
-    $this->assertIdentical($ret['test6']->data, 13, "Existing cache id test6 has the correct value.");
-    $this->assertIdentical($ret['test7']->data, 17, "Existing cache id test7 has the correct value.");
-
-    // Proceed the test a second time after deleting and setting new keys which
-    // ensures no static cache stall.
+    // Test return
+    $this->assert(isset($ret['test3']), "Existing key 3 is set");
+    $this->assert(isset($ret['test7']), "Existing key 7 is set");
+    $this->assertFalse(isset($ret['test21']), "Non existing key 21 is not set");
+    $this->assert(isset($ret['test6']), "Existing key 6 is set");
+    $this->assertFalse(isset($ret['test19']), "Non existing key 19 is not set");
+    $this->assert(isset($ret['test2']), "Existing key 2 is set");
+    // Test values
+    $this->assertIdentical($ret['test3']->data, 5, "Existing key 3 has the correct value");
+    $this->assertIdentical($ret['test7']->data, 17, "Existing key 7 has the correct value");
+    $this->assertIdentical($ret['test6']->data, 13, "Existing key 6 has the correct value");
+    $this->assertIdentical($ret['test2']->data, 3, "Existing key 2 has the correct value");
+    // Test $cids array
+    $this->assertFalse(in_array('test3', $cids), "Existing key 3 is not referenced");
+    $this->assertFalse(in_array('test7', $cids), "Existing key 7 is not referenced");
+    $this->assert(in_array('test21', $cids), "Non existing key 21 is referenced");
+    $this->assertFalse(in_array('test6', $cids), "Existing key 6 is not referenced");
+    $this->assert(in_array('test19', $cids), "Non existing key 19 is referenced");
+    $this->assertFalse(in_array('test2', $cids), "Existing key 2 is not referenced");
+
+    // Proceed the test a second time after deleting and setting new keys
+    // (ensures no static cache stall).
     $backend->delete('test3');
     $backend->delete('test6');
     $backend->set('test19', 57);
 
     $cids = $reference;
     $ret = $backend->getMultiple($cids);
-
-    // Cids that should be keys $ret array and not in $cid array.
-    $returned_cids = array(
-      'test2',
-      'test7',
-      'test19'
-    );
-    // Cids that should in $cid array and not keys $ret array.
-    $missing_cids = array(
-      'test3',
-      'test6',
-      'test21',
-    );
-
-    foreach ($returned_cids as $cid) {
-      // Should be a key in $ret.
-      $this->assert(isset($ret[$cid]), format_string("Existing cache id %cid is set in return from getMultiple().", array('%cid' => $cid)));
-      // Should not be a value in $cids.
-      $this->assertFalse(in_array($cid, $cids), format_string("Existing cache id %cid is not a value in array passed to getMultiple().", array('%cid' => $cid)));
-    }
-    foreach ($missing_cids as $cid) {
-      // Should be a not be key in $ret.
-      $this->assertFalse(isset($ret[$cid]), format_string("Non existing cache id %cid is not set.", array('%cid' => $cid)));
-      // Should be a value in $cids.
-      $this->assertTrue(in_array($cid, $cids), format_string("Non existing cache id %cid is a value in array passed to getMultiple().", array('%cid' => $cid)));
-    }
-
-    // Test return array values.
-    $this->assertIdentical($ret['test2']->data, 3, "Existing cache id test2 has the correct value.");
-    $this->assertIdentical($ret['test7']->data, 17, "Existing cache id test7 has the correct value.");
-    $this->assertIdentical($ret['test19']->data, 57, "Existing cache id test19 has the correct value.");
+    // Test return
+    $this->assertFalse(isset($ret['test3']), "Removed key 3 is not set");
+    $this->assert(isset($ret['test7']), "Existing key 7 is set");
+    $this->assertFalse(isset($ret['test21']), "Non existing key 21 is not set");
+    $this->assertFalse(isset($ret['test6']), "Removed key 6 is not set");
+    $this->assert(isset($ret['test19']), "Added key 19 is set");
+    $this->assert(isset($ret['test2']), "Existing key 2 is set");
+    // Test values
+    $this->assertIdentical($ret['test7']->data, 17, "Existing key 7 has the correct value");
+    $this->assertIdentical($ret['test19']->data, 57, "Added key 19 has the correct value");
+    $this->assertIdentical($ret['test2']->data, 3, "Existing key 2 has the correct value");
+    // Test $cids array
+    $this->assert(in_array('test3', $cids), "Removed key 3 is referenced");
+    $this->assertFalse(in_array('test7', $cids), "Existing key 7 is not referenced");
+    $this->assert(in_array('test21', $cids), "Non existing key 21 is referenced");
+    $this->assert(in_array('test6', $cids), "Removed key 6 is referenced");
+    $this->assertFalse(in_array('test19', $cids), "Added key 19 is not referenced");
+    $this->assertFalse(in_array('test2', $cids), "Existing key 2 is not referenced");
   }
 
   /**
@@ -337,8 +310,8 @@ abstract class GenericBackendUnitTestBase extends UnitTestBase {
       'test3',
       'test5',
       'test7',
-      'test19', // Non existing key should be silent
-      'test21', // Non existing key should be silent
+      'test19', // Non existing key should be silent.
+      'test21', // Non existing key should be silent.
     ));
 
     // Test if expected keys have been deleted.