diff --git a/core/tests/Drupal/Tests/Core/Datetime/DrupalDateTimeTest.php b/core/tests/Drupal/Tests/Core/Datetime/DrupalDateTimeTest.php
index 666512d..caff97c 100644
--- a/core/tests/Drupal/Tests/Core/Datetime/DrupalDateTimeTest.php
+++ b/core/tests/Drupal/Tests/Core/Datetime/DrupalDateTimeTest.php
@@ -160,7 +160,8 @@ public function providerTestInvalidDateDiff() {
    * Tests that object methods are chainable.
    */
   public function testChainable() {
-    $date = new DrupalDateTime('now', NULL, ['langcode' => 'en']);
+    $tz = new \DateTimeZone(date_default_timezone_get());
+    $date = new DrupalDateTime('now', $tz, ['langcode' => 'en']);
 
     $date->setTimestamp(12345678);
     $rendered = $date->render();
@@ -172,14 +173,3 @@ public function testChainable() {
   }
 
 }
-
-namespace Drupal\Core\Datetime;
-
-/**
- * Shadow drupal_get_user_timezone().
- *
- * @returns string
- */
-function drupal_get_user_timezone() {
-  return date_default_timezone_get();
-}