diff --git a/core/modules/image/src/Tests/ImageFieldDisplayTest.php b/core/modules/image/src/Tests/ImageFieldDisplayTest.php
index 89eb44b..2c6a2e4 100644
--- a/core/modules/image/src/Tests/ImageFieldDisplayTest.php
+++ b/core/modules/image/src/Tests/ImageFieldDisplayTest.php
@@ -343,11 +343,10 @@ function testImageFieldDefaultImage() {
 
     // Add a default image to the public image field.
     $images = $this->drupalGetTestFiles('image');
-    // $images[0] = image-test.png
-    // $images[2] = image-test.gif
     $alt = $this->randomString(512);
     $title = $this->randomString(1024);
     $edit = array(
+      // Get the path of the 'image-test.png' file.
       'files[settings_default_image_uuid]' => drupal_realpath($images[0]->uri),
       'settings[default_image][alt]' => $alt,
       'settings[default_image][title]' => $title,
@@ -380,6 +379,7 @@ function testImageFieldDefaultImage() {
     // Create alt text for the image.
     $alt = $this->randomMachineName();
 
+    // Upload the 'image-test.gif' file.
     $nid = $this->uploadNodeImage($images[2], $field_name, 'article', $alt);
     $node_storage->resetCache(array($nid));
     $node = $node_storage->load($nid);
@@ -415,6 +415,7 @@ function testImageFieldDefaultImage() {
     $this->createImageField($private_field_name, 'article', array('uri_scheme' => 'private'));
     // Add a default image to the new field.
     $edit = array(
+      // Get the path of the 'image-test.gif' file.
       'files[settings_default_image_uuid]' => drupal_realpath($images[2]->uri),
       'settings[default_image][alt]' => $alt,
       'settings[default_image][title]' => $title,
diff --git a/core/modules/system/src/Tests/Image/ToolkitGdTest.php b/core/modules/system/src/Tests/Image/ToolkitGdTest.php
index cc328f7..5ea777f 100644
--- a/core/modules/system/src/Tests/Image/ToolkitGdTest.php
+++ b/core/modules/system/src/Tests/Image/ToolkitGdTest.php
@@ -26,13 +26,6 @@ class ToolkitGdTest extends KernelTestBase {
    */
   protected $imageFactory;
 
-  /**
-   * A directory for saving processed test image files.
-   *
-   * @var string
-   */
-  protected $directory;
-
   // Colors that are used in testing.
   protected $black       = array(0, 0, 0, 0);
   protected $red         = array(255, 0, 0, 0);
@@ -41,9 +34,9 @@ class ToolkitGdTest extends KernelTestBase {
   protected $yellow      = array(255, 255, 0, 0);
   protected $white       = array(255, 255, 255, 0);
   protected $transparent = array(0, 0, 0, 127);
-  protected $whiteTransparent = array(255, 255, 255, 127);
   // Used as rotate background colors.
   protected $fuchsia            = array(255, 0, 255, 0);
+  protected $rotateTransparent = array(255, 255, 255, 127);
 
   protected $width = 40;
   protected $height = 20;
@@ -63,10 +56,6 @@ protected function setUp() {
 
     // Set the image factory service.
     $this->imageFactory = $this->container->get('image.factory');
-
-    // Prepare a directory for test file results.
-    $this->directory = $this->publicFilesDirectory .'/imagetest';
-    file_prepare_directory($this->directory, FILE_CREATE_DIRECTORY);
   }
 
   protected function checkRequirements() {
@@ -230,7 +219,7 @@ function testManipulations() {
           'arguments' => array('degrees' => 5),
           'width' => 42,
           'height' => 24,
-          'corners' => array_fill(0, 4, $this->whiteTransparent),
+          'corners' => array_fill(0, 4, $this->rotateTransparent),
         ),
         'rotate_transparent_90' => array(
           'function' => 'rotate',
@@ -263,6 +252,10 @@ function testManipulations() {
       );
     }
 
+    // Prepare a directory for test file results.
+    $directory = $this->publicFilesDirectory .'/imagetest';
+    file_prepare_directory($directory, FILE_CREATE_DIRECTORY);
+
     foreach ($files as $file) {
       foreach ($operations as $op => $values) {
         // Load up a fresh image.
@@ -319,7 +312,7 @@ function testManipulations() {
           $correct_dimensions_object = FALSE;
         }
 
-        $file_path = $this->directory . '/' . $op . image_type_to_extension($image->getToolkit()->getType());
+        $file_path = $directory . '/' . $op . image_type_to_extension($image->getToolkit()->getType());
         $image->save($file_path);
 
         $this->assertTrue($correct_dimensions_real, SafeMarkup::format('Image %file after %action action has proper dimensions.', array('%file' => $file, '%action' => $op)));
@@ -386,7 +379,7 @@ function testManipulations() {
       $image = $this->imageFactory->get();
       $image->createNew(50, 20, image_type_to_extension($type, FALSE), '#ffff00');
       $file = 'from_null' . image_type_to_extension($type);
-      $file_path = $this->directory . '/' . $file ;
+      $file_path = $directory . '/' . $file ;
       $this->assertEqual(50, $image->getWidth(), SafeMarkup::format('Image file %file has the correct width.', array('%file' => $file)));
       $this->assertEqual(20, $image->getHeight(), SafeMarkup::format('Image file %file has the correct height.', array('%file' => $file)));
       $this->assertEqual(image_type_to_mime_type($type), $image->getMimeType(), SafeMarkup::format('Image file %file has the correct MIME type.', array('%file' => $file)));
@@ -449,6 +442,10 @@ public function testResourceDestruction() {
    * Tests for GIF images with transparency.
    */
   function testGifTransparentImages() {
+    // Prepare a directory for test file results.
+    $directory = $this->publicFilesDirectory .'/imagetest';
+    file_prepare_directory($directory, FILE_CREATE_DIRECTORY);
+
     // Test loading an indexed GIF image with transparent color set.
     // Color at top-right pixel should be fully transparent.
     $file = 'image-test-transparent-indexed.gif';
@@ -456,22 +453,22 @@ function testGifTransparentImages() {
     $resource = $image->getToolkit()->getResource();
     $color_index = imagecolorat($resource, $image->getWidth() - 1, 0);
     $color = array_values(imagecolorsforindex($resource, $color_index));
-    $this->assertEqual($this->whiteTransparent, $color, SafeMarkup::format('Image %file after load has full transparent color at corner 1.', array('%file' => $file)));
+    $this->assertEqual($this->rotateTransparent, $color, "Image {$file} after load has full transparent color at corner 1.");
 
     // Test deliberately creating a GIF image with no transparent color set.
     // Color at top-right pixel should be fully transparent while in memory,
     // fully opaque after flushing image to file.
     $file = 'image-test-no-transparent-color-set.gif';
-    $file_path = $this->directory . '/' . $file ;
+    $file_path = $directory . '/' . $file ;
     // Create image.
     $image = $this->imageFactory->get();
     $image->createNew(50, 20, 'gif', NULL);
     $resource = $image->getToolkit()->getResource();
     $color_index = imagecolorat($resource, $image->getWidth() - 1, 0);
     $color = array_values(imagecolorsforindex($resource, $color_index));
-    $this->assertEqual($this->whiteTransparent, $color, 'New GIF image with no transparent color set after creation has full transparent color at corner 1.');
+    $this->assertEqual($this->whiteTransparent, $color, "New GIF image with no transparent color set after creation has full transparent color at corner 1.");
     // Save image.
-    $this->assertTrue($image->save($file_path), SafeMarkup::format('New GIF image %file was saved.', array('%file' => $file)));
+    $this->assertTrue($image->save($file_path), "New GIF image {$file} was saved.");
     // Reload image.
     $image_reloaded = $this->imageFactory->get($file_path);
     $resource = $image_reloaded->getToolkit()->getResource();
@@ -479,7 +476,7 @@ function testGifTransparentImages() {
     $color = array_values(imagecolorsforindex($resource, $color_index));
     // Check explicitly for alpha == 0 as the rest of the color has been
     // compressed and may have slight difference from full white.
-    $this->assertEqual(0, $color[3], SafeMarkup::format('New GIF image %file after reload has no transparent color at corner 1.', array('%file' => $file)));
+    $this->assertEqual(0, $color[3], "New GIF image {$file} after reload has no transparent color at corner 1.");
 
     // Test loading an image whose transparent color index is out of range.
     // This image was generated by taking an initial image with a palette size