diff --git a/core/lib/Drupal/Core/Template/Attribute.php b/core/lib/Drupal/Core/Template/Attribute.php
index 076cfd3..e9ede3b 100644
--- a/core/lib/Drupal/Core/Template/Attribute.php
+++ b/core/lib/Drupal/Core/Template/Attribute.php
@@ -6,6 +6,7 @@
  */
 
 namespace Drupal\Core\Template;
+use Drupal\Component\Utility\String;
 
 
 /**
@@ -103,7 +104,7 @@ public function __toString() {
     $return = '';
     foreach ($this->storage as $name => $value) {
       if (!$value->printed()) {
-        $rendered = is_object($value) ? $value->render() : (check_plain($name) . ' = "' . check_plain($value) . '"');
+        $rendered = is_object($value) ? $value->render() : (String::checkPlain($name) . ' = "' . String::checkPlain($value) . '"');
         if ($rendered) {
           $return .= " $rendered";
         }
@@ -133,8 +134,8 @@ public function getIterator() {
   /**
    * Returns the whole array.
    */
-  public function value() {
-    return $this->value;
+  public function storage() {
+    return $this->storage;
   }
 
 }
diff --git a/core/lib/Drupal/Core/Template/AttributeBoolean.php b/core/lib/Drupal/Core/Template/AttributeBoolean.php
index 48ca388..ecd1dcf 100644
--- a/core/lib/Drupal/Core/Template/AttributeBoolean.php
+++ b/core/lib/Drupal/Core/Template/AttributeBoolean.php
@@ -6,6 +6,7 @@
  */
 
 namespace Drupal\Core\Template;
+use Drupal\Component\Utility\String;
 
 /**
  * A class that defines a type of boolean HTML attribute.
@@ -41,7 +42,7 @@ public function render() {
    */
   public function __toString() {
     $this->printed = TRUE;
-    return $this->value === FALSE ? '' : check_plain($this->name);
+    return $this->value === FALSE ? '' : String::checkPlain($this->name);
   }
 
 }
diff --git a/core/tests/Drupal/Tests/Core/Template/AttributeTest.php b/core/tests/Drupal/Tests/Core/Template/AttributeTest.php
new file mode 100644
index 0000000..f0abdd9
--- /dev/null
+++ b/core/tests/Drupal/Tests/Core/Template/AttributeTest.php
@@ -0,0 +1,114 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Tests\Core\Template\AttributeTest.
+ */
+
+namespace Drupal\Tests\Core\Template;
+
+use Drupal\Core\Template\Attribute;
+use Drupal\Core\Template\AttributeArray;
+use Drupal\Core\Template\AttributeString;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * Tests the template attribute class.
+ *
+ * @see \Drupal\Core\Template\Attribute
+ */
+class AttributeTest extends UnitTestCase {
+
+  public static function getInfo() {
+    return array(
+      'name' => 'Attribute class',
+      'description' => 'Tests the template attribute class.',
+      'group' => 'Template',
+    );
+  }
+
+  /**
+   * Tests the constructor of the attribute class.
+   */
+  public function testConstructor() {
+    $attribute = new Attribute(array('class' => array('example-class')));
+    $this->assertTrue(isset($attribute['class']));
+    $this->assertEquals(new AttributeArray('class', array('example-class')), $attribute['class']);
+  }
+
+  /**
+   * Tests set of values.
+   */
+  public function testSet() {
+    $attribute = new Attribute();
+    $attribute['class'] = array('example-class');
+
+    $this->assertTrue(isset($attribute['class']));
+    $this->assertEquals(new AttributeArray('class', array('example-class')), $attribute['class']);
+  }
+
+  /**
+   * Tests adding new values to an existing part of the attribute.
+   */
+  public function testAdd() {
+    $attribute = new Attribute(array('class' => array('example-class')));
+
+    $attribute['class'][] = 'other-class';
+    $this->assertEquals(new AttributeArray('class', array('example-class', 'other-class')), $attribute['class']);
+  }
+
+  /**
+   * Tests removing of values.
+   */
+  public function testRemove() {
+    $attribute = new Attribute(array('class' => array('example-class')));
+    unset($attribute['class']);
+    $this->assertFalse(isset($attribute['class']));
+  }
+
+  /**
+   * Tests iterating on the values of the attribute.
+   */
+  public function testIterate() {
+    $attribute = new Attribute(array('class' => array('example-class'), 'id' => 'example-id'));
+
+    $counter = 0;
+    foreach ($attribute as $key => $value) {
+      if ($counter == 0) {
+        $this->assertEquals('class', $key);
+        $this->assertEquals(new AttributeArray('class', array('example-class')), $value);
+      }
+      if ($counter == 1) {
+        $this->assertEquals('id', $key);
+        $this->assertEquals(new AttributeString('id', 'example-id'), $value);
+      }
+      $counter++;
+    }
+  }
+
+  /**
+   * Tests printing of an attribute.
+   */
+  public function testPrint() {
+    $attribute = new Attribute(array('class' => array('example-class'), 'id' => 'example-id', 'enabled' => TRUE));
+
+    $html = '<div' . (string) $attribute . '></div>';
+    $this->assertSelectEquals('div.example-class', '', 1, $html);
+    $this->assertSelectEquals('div.example-class2', '', 0, $html);
+
+    $this->assertSelectEquals('div#example-id', '', 1, $html);
+    $this->assertSelectEquals('div#example-id2', '', 0, $html);
+
+    $this->assertTrue(strpos($html, 'enabled') === 0);
+  }
+
+  /**
+   * Tests the storage method.
+   */
+  public function testStorage() {
+    $attribute = new Attribute(array('class' => array('example-class')));
+
+    $this->assertEquals(array('class' => new AttributeArray('class', array('example-class'))), $attribute->storage());
+  }
+
+}