.../BlockContent/BlockContentResourceTestBase.php       |  2 --
 .../ContactForm/ContactFormResourceTestBase.php         |  2 --
 .../EntityTestBundleResourceTestBase.php                |  2 --
 .../EntityResource/Media/MediaResourceTestBase.php      | 17 ++++++++++++-----
 .../tests/src/Kernel/EntitySerializationTest.php        |  7 ++++---
 5 files changed, 16 insertions(+), 14 deletions(-)

diff --git a/core/modules/rest/tests/src/Functional/EntityResource/BlockContent/BlockContentResourceTestBase.php b/core/modules/rest/tests/src/Functional/EntityResource/BlockContent/BlockContentResourceTestBase.php
index 8b67cc6..dfa7742 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/BlockContent/BlockContentResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/BlockContent/BlockContentResourceTestBase.php
@@ -12,8 +12,6 @@
  */
 abstract class BlockContentResourceTestBase extends EntityResourceTestBase {
 
-  use BcTimestampNormalizerUnixTestTrait;
-
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/rest/tests/src/Functional/EntityResource/ContactForm/ContactFormResourceTestBase.php b/core/modules/rest/tests/src/Functional/EntityResource/ContactForm/ContactFormResourceTestBase.php
index 51e297a..595de0d 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/ContactForm/ContactFormResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/ContactForm/ContactFormResourceTestBase.php
@@ -8,8 +8,6 @@
 
 abstract class ContactFormResourceTestBase extends EntityResourceTestBase {
 
-  use BcTimestampNormalizerUnixTestTrait;
-
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/rest/tests/src/Functional/EntityResource/EntityTestBundle/EntityTestBundleResourceTestBase.php b/core/modules/rest/tests/src/Functional/EntityResource/EntityTestBundle/EntityTestBundleResourceTestBase.php
index f43d877..bb42717 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/EntityTestBundle/EntityTestBundleResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/EntityTestBundle/EntityTestBundleResourceTestBase.php
@@ -8,8 +8,6 @@
 
 abstract class EntityTestBundleResourceTestBase extends EntityResourceTestBase {
 
-  use BcTimestampNormalizerUnixTestTrait;
-
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/rest/tests/src/Functional/EntityResource/Media/MediaResourceTestBase.php b/core/modules/rest/tests/src/Functional/EntityResource/Media/MediaResourceTestBase.php
index 475a1ca..d829e77 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/Media/MediaResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/Media/MediaResourceTestBase.php
@@ -11,8 +11,6 @@
 
 abstract class MediaResourceTestBase extends EntityResourceTestBase {
 
-  use BcTimestampNormalizerUnixTestTrait;
-
   /**
    * {@inheritdoc}
    */
@@ -175,13 +173,22 @@ protected function getExpectedNormalizedEntity() {
         ],
       ],
       'created' => [
-        $this->formatExpectedTimestampItemValues(123456789),
+        [
+          'value' => (new \DateTime())->setTimestamp(123456789)->setTimezone(new \DateTimeZone('UTC'))->format(\DateTime::RFC3339),
+          'format' => \DateTime::RFC3339,
+        ],
       ],
       'changed' => [
-        $this->formatExpectedTimestampItemValues($this->entity->getChangedTime()),
+        [
+          'value' => (new \DateTime())->setTimestamp((int) $this->entity->getChangedTime())->setTimezone(new \DateTimeZone('UTC'))->format(\DateTime::RFC3339),
+          'format' => \DateTime::RFC3339,
+        ],
       ],
       'revision_created' => [
-        $this->formatExpectedTimestampItemValues((int) $this->entity->getRevisionCreationTime()),
+        [
+          'value' => (new \DateTime())->setTimestamp((int) $this->entity->getRevisionCreationTime())->setTimezone(new \DateTimeZone('UTC'))->format(\DateTime::RFC3339),
+          'format' => \DateTime::RFC3339,
+        ],
       ],
       'default_langcode' => [
         [
diff --git a/core/modules/serialization/tests/src/Kernel/EntitySerializationTest.php b/core/modules/serialization/tests/src/Kernel/EntitySerializationTest.php
index 5b71b93..5bde06b 100644
--- a/core/modules/serialization/tests/src/Kernel/EntitySerializationTest.php
+++ b/core/modules/serialization/tests/src/Kernel/EntitySerializationTest.php
@@ -13,8 +13,6 @@
  */
 class EntitySerializationTest extends NormalizerTestBase {
 
-  use BcTimestampNormalizerUnixTestTrait;
-
   /**
    * Modules to install.
    *
@@ -109,7 +107,10 @@ public function testNormalize() {
         ['value' => 'entity_test_mulrev'],
       ],
       'created' => [
-        $this->formatExpectedTimestampItemValues($this->entity->created->value),
+        [
+          'value' => (new \DateTime())->setTimestamp((int) $this->entity->get('created')->value)->setTimezone(new \DateTimeZone('UTC'))->format(\DateTime::RFC3339),
+          'format' => \DateTime::RFC3339,
+        ],
       ],
       'user_id' => [
         [