diff -u b/core/modules/color/src/Tests/ColorSafePreviewTest.php b/core/modules/color/src/Tests/ColorSafePreviewTest.php
--- b/core/modules/color/src/Tests/ColorSafePreviewTest.php
+++ b/core/modules/color/src/Tests/ColorSafePreviewTest.php
@@ -20,9 +20,9 @@
   /**
    * Modules to enable.
    *
-   * @var array
+   * @var string[]
    */
-  public static $modules = array('color', 'color_test');
+  public static $modules = ['color', 'color_test'];
 
   /**
    * A user with administrative permissions.
@@ -38,7 +38,7 @@
     parent::setUp();
 
     // Create user.
-    $this->bigUser = $this->drupalCreateUser(array('administer themes'));
+    $this->bigUser = $this->drupalCreateUser(['administer themes']);
   }
 
   /**
@@ -46,9 +46,9 @@
    */
   function testColorPreview() {
     // Install the test theme
-    \Drupal::service('theme_handler')->install(array('color_test_theme'));
+    \Drupal::service('theme_handler')->install(['color_test_theme']);
 
-    $url_object = Url::fromRoute('system.theme_settings_theme', array('theme' => 'color_test_theme'));
+    $url_object = Url::fromRoute('system.theme_settings_theme', ['theme' => 'color_test_theme']);
 
     $this->drupalLogin($this->bigUser);
     $this->drupalGet($url_object);