diff --git a/core/modules/datetime/tests/src/Functional/EntityResource/EntityTest/EntityTestDatetimeTest.php b/core/modules/datetime/tests/src/Functional/EntityResource/EntityTest/EntityTestDatetimeTest.php
index 0c75233..c0937d7 100644
--- a/core/modules/datetime/tests/src/Functional/EntityResource/EntityTest/EntityTestDatetimeTest.php
+++ b/core/modules/datetime/tests/src/Functional/EntityResource/EntityTest/EntityTestDatetimeTest.php
@@ -68,6 +68,14 @@ public function setUp() {
     $this->entity->save();
   }
 
+  public function testWTF() {
+    $value = $this->entity->field_datetime->value;
+    $date = $this->entity->field_datetime->date;
+
+    $this->assertEquals(static::$dateString, $value);
+    $this->assertEquals(static::$dateString . '+00:00', $date->format('c'));
+  }
+
   /**
    * {@inheritdoc}
    */
@@ -90,7 +98,7 @@ protected function getExpectedNormalizedEntity() {
     return parent::getExpectedNormalizedEntity() + [
       static::$fieldName => [
         [
-          'value' => '2017-03-01T20:02:00+11:00',
+          'value' => static::$dateString . '+11:00',
         ],
       ],
     ];
diff --git a/core/modules/rest/tests/src/Functional/BcTimestampNormalizerUnixTestTrait.php b/core/modules/rest/tests/src/Functional/BcTimestampNormalizerUnixTestTrait.php
index ae0668a..3ba5d32 100644
--- a/core/modules/rest/tests/src/Functional/BcTimestampNormalizerUnixTestTrait.php
+++ b/core/modules/rest/tests/src/Functional/BcTimestampNormalizerUnixTestTrait.php
@@ -29,9 +29,11 @@ protected function formatExpectedTimestampItemValues($timestamp) {
 
     // Otherwise, format the date string to the same that
     // \Drupal\serialization\Normalizer\TimestampItemNormalizer will produce.
+    // 'Australia/Sydney' is the default time zone for tests. It is hardcoded
+    // here for test cases where the config isn't available.
     $date = new \DateTime();
     $date->setTimestamp($timestamp);
-    $date->setTimezone(new \DateTimeZone($this->config('system.date')->get('timezone.default')));
+    $date->setTimezone(new \DateTimeZone('Australia/Sydney'));
 
     // Format is also added to the expected return values.
     return [