diff --git a/core/lib/Drupal/Component/Plugin/DefaultPluginBag.php b/core/lib/Drupal/Component/Plugin/DefaultPluginBag.php
index 15c85d0..7e943df 100644
--- a/core/lib/Drupal/Component/Plugin/DefaultPluginBag.php
+++ b/core/lib/Drupal/Component/Plugin/DefaultPluginBag.php
@@ -48,7 +48,7 @@ class DefaultPluginBag extends PluginBag {
    *
    * @var array
    */
-  protected $originalOrder;
+  protected $originalOrder = array();
 
   /**
    * Constructs a new DefaultPluginBag object.
diff --git a/core/tests/Drupal/Tests/Component/Plugin/DefaultPluginBagTest.php b/core/tests/Drupal/Tests/Component/Plugin/DefaultPluginBagTest.php
index e844dcc..01c652f 100644
--- a/core/tests/Drupal/Tests/Component/Plugin/DefaultPluginBagTest.php
+++ b/core/tests/Drupal/Tests/Component/Plugin/DefaultPluginBagTest.php
@@ -47,9 +47,9 @@ class DefaultPluginBagTest extends UnitTestCase {
    * @var array
    */
   protected $config = array(
-    'apple' => array('id' => 'apple', 'key' => 'value'),
     'banana' => array('id' => 'banana', 'key' => 'value'),
     'cherry' => array('id' => 'cherry', 'key' => 'value'),
+    'apple' => array('id' => 'apple', 'key' => 'value'),
   );
 
   public static function getInfo() {
@@ -94,7 +94,7 @@ protected function setUp() {
   public function testHas() {
     $definitions = $this->getPluginDefinitions();
 
-    $this->assertFalse($this->defaultPluginBag->has($this->randomName()), 'Non existing plugin found.');
+    $this->assertFalse($this->defaultPluginBag->has($this->randomName()), 'Nonexistent plugin found.');
 
     foreach (array_keys($definitions) as $plugin_id) {
       $this->assertTrue($this->defaultPluginBag->has($plugin_id));
@@ -192,11 +192,27 @@ public function testSortHelper($plugin_id_1, $plugin_id_2, $expected) {
   }
 
   /**
-   * Tests the sort method.
+   * Tests the configuration getter method.
    *
-   * @see \Drupal\Component\Plugin\DefaultPluginBag::sort()
+   * @see \Drupal\Component\Plugin\DefaultPluginBag::getConfiguration()
    */
-  public function testSort() {
+  public function testGetConfiguration() {
+    // The expected order matches $this->config.
+    $expected = array('banana', 'cherry', 'apple');
+
+    $config = $this->defaultPluginBag->getConfiguration();
+    $this->assertSame($expected, array_keys($config), 'The order of the configuration is unchanged.');
+
+    $ids = $this->defaultPluginBag->getInstanceIDs();
+    $this->assertSame($expected, array_keys($ids), 'The order of the instances is unchanged.');
+
+    $this->defaultPluginBag->sort();
+    $config = $this->defaultPluginBag->getConfiguration();
+    $this->assertSame($expected, array_keys($config), 'After sorting, the order of the configuration is unchanged.');
+
+    $ids = $this->defaultPluginBag->getInstanceIDs();
+    sort($expected);
+    $this->assertSame($expected, array_keys($ids), 'After sorting, the order of the instances is also sorted.');
   }
 
 }