diff --git a/core/tests/Drupal/Tests/Core/Image/ImageTest.php b/core/tests/Drupal/Tests/Core/Image/ImageTest.php
index 71bcd53..58a848e 100644
--- a/core/tests/Drupal/Tests/Core/Image/ImageTest.php
+++ b/core/tests/Drupal/Tests/Core/Image/ImageTest.php
@@ -64,7 +64,7 @@ protected function setUp() {
    */
   protected function getToolkitMock(array $stubs = array()) {
     $mock_builder = $this->getMockBuilder('Drupal\system\Plugin\ImageToolkit\GDToolkit');
-    $stubs += array('getPluginId', 'save');
+    $stubs = array_merge(array('getPluginId', 'save'), $stubs);
     return $mock_builder
       ->disableOriginalConstructor()
       ->setMethods($stubs)
@@ -92,15 +92,18 @@ protected function getToolkitOperationMock($class_name, ImageToolkitInterface $t
   /**
    * Get an image with a mocked toolkit, for testing.
    *
+   * @param bool $load_expected
+   *   (optional) Whether the load() method is expected to ba called. Defaults
+   *   to TRUE.
    * @param array $stubs
    *   (optional) Array containing toolkit methods to be replaced with stubs.
    *
    * @return \Drupal\Core\Image\Image
    *   An image object.
    */
-  protected function getTestImage($loadExpected = TRUE, array $stubs = array()) {
-    if (!$loadExpected && !in_array('load', $stubs)) {
-      $stubs += array('load');
+  protected function getTestImage($load_expected = TRUE, array $stubs = array()) {
+    if (!$load_expected && !in_array('load', $stubs)) {
+      $stubs = array_merge(array('load'), $stubs);
     }
 
     $this->toolkit = $this->getToolkitMock($stubs);
@@ -109,7 +112,7 @@ protected function getTestImage($loadExpected = TRUE, array $stubs = array()) {
       ->method('getPluginId')
       ->will($this->returnValue('gd'));
 
-    if (!$loadExpected) {
+    if (!$load_expected) {
       $this->toolkit->expects($this->never())
         ->method('load');
     }
@@ -127,7 +130,7 @@ protected function getTestImage($loadExpected = TRUE, array $stubs = array()) {
    *   An image object.
    */
   protected function getTestImageForOperation($class_name) {
-    $this->toolkit = $this->getToolkitMock(array('getToolkitOperation', 'getPluginId'));
+    $this->toolkit = $this->getToolkitMock(array('getToolkitOperation'));
     $this->toolkitOperation = $this->getToolkitOperationMock($class_name, $this->toolkit);
 
     $this->toolkit->expects($this->any())