diff --git a/core/lib/Drupal/Core/Cache/DatabaseBackend.php b/core/lib/Drupal/Core/Cache/DatabaseBackend.php
index 828a4c6..4118cab 100644
--- a/core/lib/Drupal/Core/Cache/DatabaseBackend.php
+++ b/core/lib/Drupal/Core/Cache/DatabaseBackend.php
@@ -42,11 +42,6 @@ class DatabaseBackend implements CacheBackendInterface {
   protected $checksumProvider;
 
   /**
-   * @var boolean
-   */
-  protected $useMbstring;
-
-  /**
    * Constructs a DatabaseBackend object.
    *
    * @param \Drupal\Core\Database\Connection $connection
@@ -63,9 +58,6 @@ public function __construct(Connection $connection, CacheTagsChecksumInterface $
     $this->bin = $bin;
     $this->connection = $connection;
     $this->checksumProvider = $checksum_provider;
-
-    // check if mb_check_encoding function is present
-    $this->useMbstring = function_exists('mb_check_encoding');
   }
 
   /**
@@ -429,17 +421,19 @@ protected function normalizeCid($cid) {
   }
 
   /**
-   * Checks to see if a given string is only made up of ascii characters
-   * Uses mb_check_encoding if present, otherwise falls back to preg_match
+   * Checks to see if a given string is only made up of ascii characters.
+   *
+   * This uses mb_check_encoding if that's present, otherwise this falls back
+   * to preg_match.
    *
    * @param string $text
-   *   the text to check
+   *   The text to check.
    *
    * @return boolean
-   *   true if $text only contains ascii characters, otherwise false
+   *   True if $text only contains ascii characters, otherwise false.
    */
   protected function isAscii($text) {
-    if ($this->useMbstring) {
+    if ($this->mbStringExists()) {
       return mb_check_encoding($text, 'ASCII');
     }
     else {
@@ -448,6 +442,14 @@ protected function isAscii($text) {
   }
 
   /**
+   * Check if mb_check_encoding function is present.
+   * @return bool
+   */
+  protected function mbStringExists() {
+    return function_exists('mb_check_encoding');
+  }
+
+  /**
    * Defines the schema for the {cache_*} bin tables.
    */
   public function schemaDefinition() {
diff --git a/core/modules/system/src/Tests/Cache/DatabaseBackendUnitTest.php b/core/modules/system/src/Tests/Cache/DatabaseBackendUnitTest.php
index 934fe81..ccec3e8 100644
--- a/core/modules/system/src/Tests/Cache/DatabaseBackendUnitTest.php
+++ b/core/modules/system/src/Tests/Cache/DatabaseBackendUnitTest.php
@@ -53,4 +53,108 @@ public function testSetGet() {
     $this->assertIdentical($cached_value_short, $backend->get($cid_short)->data, "Backend contains the correct value for short, non-ASCII cache id.");
   }
 
+  /**
+   * Tests if the correct function is chosen.
+   */
+  function testAsciiFunctionSelection() {
+
+    // Make method and variable accessible through reflection.
+    $reflection_class = new \ReflectionClass("Drupal\\Core\\Cache\\DatabaseBackend");
+    $reflection_property = $reflection_class->getMethod('mbStringExists');
+    $reflection_property->setAccessible(TRUE);
+
+    // Create classes.
+    $mockedConnection = $this->getMockBuilder("Drupal\\Core\\Database\\Connection")
+      ->disableOriginalConstructor()
+      ->getMock();
+    $mockedChecksumInterface = $this->getMockBuilder("Drupal\\Core\\Cache\\CacheTagsChecksumInterface")
+      ->getMock();
+
+    $db_cache = new DatabaseBackend(
+      $mockedConnection,
+      $mockedChecksumInterface,
+      'test'
+    );
+
+    if (function_exists('mb_check_encoding')) {
+      $this->assertTrue(
+        $reflection_property->getValue($db_cache),
+        "Assert that mbstring will be used."
+      );
+    }
+    else {
+      $this->assertFalse(
+        $reflection_property->getValue($db_cache),
+        "Assert that mbstring will not be used."
+      );
+    }
+
+  }
+
+  /**
+   * Tests that the DatabaseBackend normalizeCid works.
+   */
+  function testCidNormalization() {
+
+    $cids = array(
+      // Ascii only, should return same.
+      array("cid" => "0000000000", "expected" => "0000000000"),
+      // Utf-8, should return hash.
+      array(
+        "cid" => "Some Danish characters: � �",
+        "expected" => "6Q10YnfEtF092na6OZOwuLniGFilOQgIPnam3IXjcBU"
+      ),
+      // Ascii, over 255 characters long, should return hash padded with
+      // original string to a 255 length.
+      array(
+        "cid" => str_repeat("0", 256),
+        "expected" => "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000Z_AiGV7kBRQpaMobU64lE6i6sEBNcFd3hTFvqVIY6Lo"
+      ),
+      // Utf-8, over 255 long, should return a hash.
+      array(
+        "cid" => "Some Danish characters: � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �",
+        "expected" => "KbjIhg-2SJ5fjtlNol8DnT_tJDr65kcJsq9cpgLSVJ0"
+      ),
+    );
+
+    // Make method and variable accessible through reflection.
+    $reflection_class = new \ReflectionClass("Drupal\Core\Cache\DatabaseBackend");
+    $reflection_property = $reflection_class->getMethod('mbStringExists');
+    $reflection_property->setAccessible(TRUE);
+    $reflection_method = $reflection_class->getMethod('normalizeCid');
+    $reflection_method->setAccessible(TRUE);
+
+    // Create classes.
+    $mockedConnection = $this->getMockBuilder("Drupal\Core\Database\Connection")
+      ->disableOriginalConstructor()
+      ->getMock();
+    $mockedChecksumInterface = $this
+      ->getMockBuilder("Drupal\Core\Cache\CacheTagsChecksumInterface")
+      ->getMock();
+
+    $db_cache = new DatabaseBackend($mockedConnection, $mockedChecksumInterface, 'test');
+
+    if (function_exists('mb_check_encoding')) {
+      // run checks
+      foreach ($cids as $cid) {
+        $this->assertEquals(
+          $cid["expected"],
+          $reflection_method->invoke($db_cache, $cid["cid"]),
+          "Assert that cid is normalized as expected."
+        );
+      }
+    }
+
+    // now force usage of preg
+    $reflection_property->setValue($db_cache, FALSE);
+    foreach ($cids as $cid) {
+      $this->assertEquals(
+        $cid["expected"],
+        $reflection_method->invoke($db_cache, $cid["cid"]),
+        "Assert that cid is normalized as expected."
+      );
+    }
+
+  }
+
 }
diff --git a/core/tests/Drupal/Tests/Core/Cache/DatabaseBackendTest.php b/core/tests/Drupal/Tests/Core/Cache/DatabaseBackendTest.php
deleted file mode 100644
index 6511e0d..0000000
--- a/core/tests/Drupal/Tests/Core/Cache/DatabaseBackendTest.php
+++ /dev/null
@@ -1,91 +0,0 @@
-<?php
-
-/**
- * @file
- * Contains \Drupal\Tests\Core\Cache\DatabaseBackendTest.
- */
-
-namespace Drupal\Tests\Core\Cache;
-
-use Drupal\Core\Cache\DatabaseBackend;
-use Drupal\Tests\UnitTestCase;
-
-/**
- * Tests the cache DatabaseBackend.
- *
- * @group Cache
- */
-class DatabaseBackendTest extends UnitTestCase
-{
-
-    /**
-     * Tests if the correct function is choosen
-     */
-    function testAsciiFunctionSelection()
-    {
-
-        // make method and variable accessible through reflection
-        $reflection_class = new \ReflectionClass("Drupal\Core\Cache\DatabaseBackend");
-        $reflection_property = $reflection_class->getProperty('useMbstring');
-        $reflection_property->setAccessible(TRUE);
-
-        // create classes
-        $mockedConnection = $this->getMockBuilder("Drupal\Core\Database\Connection")->disableOriginalConstructor()->getMock();
-        $mockedChecksumInterface = $this->getMockBuilder("Drupal\Core\Cache\CacheTagsChecksumInterface")->getMock();
-
-        $db_cache = new DatabaseBackend($mockedConnection, $mockedChecksumInterface, 'test');
-
-        if (function_exists('mb_check_encoding')) {
-            $this->assertTrue($reflection_property->getValue($db_cache), "Assert that mbstring will be used");
-        }
-        else {
-            $this->assertFalse($reflection_property->getValue($db_cache), "Assert that mbstring will not be used");
-        }
-
-    }
-
-    /**
-     * Tests that the DatabaseBackend normalizeCid works both with or without mbstring.
-     */
-    function testCidNormalization()
-    {
-
-        $cids = array(
-            // ascii only, should return same
-            array("cid" => "0000000000", "expected" => "0000000000"),
-            // utf-8, should return hash
-            array("cid" => "Some Danish characters: æ ø", "expected" => "6Q10YnfEtF092na6OZOwuLniGFilOQgIPnam3IXjcBU"),
-            // ascii, over 255 long, should return hash padded with original string to a 255 length
-            array("cid" => str_repeat("0", 256), "expected" => "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000Z_AiGV7kBRQpaMobU64lE6i6sEBNcFd3hTFvqVIY6Lo"),
-            // utf-8, over 255 long, should return hash
-            array("cid" => "Some Danish characters: æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø æ ø", "expected" => "KbjIhg-2SJ5fjtlNol8DnT_tJDr65kcJsq9cpgLSVJ0"),
-        );
-
-        // make method and variable accessible through reflection
-        $reflection_class = new \ReflectionClass("Drupal\Core\Cache\DatabaseBackend");
-        $reflection_property = $reflection_class->getProperty('useMbstring');
-        $reflection_property->setAccessible(TRUE);
-        $reflection_method = $reflection_class->getMethod('normalizeCid');
-        $reflection_method->setAccessible(TRUE);
-
-        // create classes
-        $mockedConnection = $this->getMockBuilder("Drupal\Core\Database\Connection")->disableOriginalConstructor()->getMock();
-        $mockedChecksumInterface = $this->getMockBuilder("Drupal\Core\Cache\CacheTagsChecksumInterface")->getMock();
-
-        $db_cache = new DatabaseBackend($mockedConnection, $mockedChecksumInterface, 'test');
-
-        if (function_exists('mb_check_encoding')) {
-            // run checks
-            foreach ($cids as $cid) {
-                $this->assertEquals($cid["expected"], $reflection_method->invoke($db_cache, $cid["cid"]), "Assert that cid is normalized as expected");
-            }
-        }
-
-        // now force usage of preg
-        $reflection_property->setValue($db_cache, FALSE);
-        foreach ($cids as $cid) {
-            $this->assertEquals($cid["expected"], $reflection_method->invoke($db_cache, $cid["cid"]), "Assert that cid is normalized as expected");
-        }
-
-    }
-}