diff --git a/core/modules/image/src/Tests/ImageFieldDisplayTest.php b/core/modules/image/src/Tests/ImageFieldDisplayTest.php
index b73c06f..780abd9 100644
--- a/core/modules/image/src/Tests/ImageFieldDisplayTest.php
+++ b/core/modules/image/src/Tests/ImageFieldDisplayTest.php
@@ -17,8 +17,6 @@
  */
 class ImageFieldDisplayTest extends ImageFieldTestBase {
 
-  protected $dumpHeaders = TRUE;
-
   /**
    * Modules to enable.
    *
@@ -58,7 +56,7 @@ function _testImageFieldFormatters($scheme) {
     $this->assertLinkByHref(\Drupal::url('image.style_list'), 0, 'Link to image styles configuration is found');
 
     // Remove 'administer image styles' permission from testing admin user.
-    $admin_user_roles = $this->admin_user->getRoles(TRUE);
+    $admin_user_roles = $this->adminUser->getRoles(TRUE);
     user_role_change_permissions(reset($admin_user_roles), array('administer image styles' => FALSE));
 
     // Go to manage display page again.
@@ -127,7 +125,7 @@ function _testImageFieldFormatters($scheme) {
       $this->assertResponse('403', 'Access denied to original image as anonymous user.');
 
       // Log in again.
-      $this->drupalLogin($this->admin_user);
+      $this->drupalLogin($this->adminUser);
     }
 
     // Test the image linked to content formatter.
diff --git a/core/modules/image/src/Tests/ImageFieldTestBase.php b/core/modules/image/src/Tests/ImageFieldTestBase.php
index 2b8a648..d8bee12 100644
--- a/core/modules/image/src/Tests/ImageFieldTestBase.php
+++ b/core/modules/image/src/Tests/ImageFieldTestBase.php
@@ -34,7 +34,12 @@
    */
   public static $modules = array('node', 'image', 'field_ui', 'image_module_test');
 
-  protected $admin_user;
+  /**
+   * An user with permissions to administer content types and image styles.
+   *
+   * @var \Drupal\user\UserInterface
+   */
+  protected $adminUser;
 
   protected function setUp() {
     parent::setUp();
@@ -45,8 +50,8 @@ protected function setUp() {
       $this->drupalCreateContentType(array('type' => 'article', 'name' => 'Article'));
     }
 
-    $this->admin_user = $this->drupalCreateUser(array('access content', 'access administration pages', 'administer site configuration', 'administer content types', 'administer node fields', 'administer nodes', 'create article content', 'edit any article content', 'delete any article content', 'administer image styles', 'administer node display'));
-    $this->drupalLogin($this->admin_user);
+    $this->adminUser = $this->drupalCreateUser(array('access content', 'access administration pages', 'administer site configuration', 'administer content types', 'administer node fields', 'administer nodes', 'create article content', 'edit any article content', 'delete any article content', 'administer image styles', 'administer node display'));
+    $this->drupalLogin($this->adminUser);
   }
 
   /**