.../src/Normalizer/DateTimeNormalizer.php          |  3 +++
 .../TimeStampItemNormalizerTraitDeprecatedTest.php | 25 ++++++++++++++++++++++
 ...StampItemNormalizerTraitDeprecatedTestClass.php | 14 ++++++++++++
 3 files changed, 42 insertions(+)

diff --git a/core/modules/serialization/src/Normalizer/DateTimeNormalizer.php b/core/modules/serialization/src/Normalizer/DateTimeNormalizer.php
index 350aea4dc6..8e62c30972 100644
--- a/core/modules/serialization/src/Normalizer/DateTimeNormalizer.php
+++ b/core/modules/serialization/src/Normalizer/DateTimeNormalizer.php
@@ -43,6 +43,9 @@ class DateTimeNormalizer extends NormalizerBase implements DenormalizerInterface
 
   /**
    * Constructs a new DateTimeNormalizer instance.
+   *
+   * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
+   *   A config factory for retrieving required config objects.
    */
   public function __construct(ConfigFactoryInterface $config_factory) {
     $this->systemDateConfig = $config_factory->get('system.date');
diff --git a/core/modules/serialization/tests/src/Unit/Normalizer/TimeStampItemNormalizerTraitDeprecatedTest.php b/core/modules/serialization/tests/src/Unit/Normalizer/TimeStampItemNormalizerTraitDeprecatedTest.php
new file mode 100644
index 0000000000..77623a190f
--- /dev/null
+++ b/core/modules/serialization/tests/src/Unit/Normalizer/TimeStampItemNormalizerTraitDeprecatedTest.php
@@ -0,0 +1,25 @@
+<?php
+
+namespace Drupal\Tests\serialization\Unit\Normalizer;
+
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * Tests that TimeStampItemNormalizerTrait throws a deprecation error.
+ *
+ * @group serialization
+ * @group legacy
+ * @coversDefaultClass \Drupal\serialization\Normalizer\TimeStampItemNormalizerTrait
+ */
+class TimeStampItemNormalizerTraitDeprecatedTest extends UnitTestCase {
+
+  /**
+   * Tests that TimeStampItemNormalizerTrait throws a deprecation error.
+   *
+   * @expectedDeprecation Drupal\serialization\Normalizer\TimeStampItemNormalizerTrait is deprecated in Drupal 8.7.0 and will be removed in Drupal 9.0.0. Use \Drupal\serialization\Normalizer\TimestampNormalizer instead.
+   */
+  public function testDeprecated() {
+    $test = new TimeStampItemNormalizerTraitDeprecatedTestClass();
+  }
+
+}
diff --git a/core/modules/serialization/tests/src/Unit/Normalizer/TimeStampItemNormalizerTraitDeprecatedTestClass.php b/core/modules/serialization/tests/src/Unit/Normalizer/TimeStampItemNormalizerTraitDeprecatedTestClass.php
new file mode 100644
index 0000000000..82f37ae056
--- /dev/null
+++ b/core/modules/serialization/tests/src/Unit/Normalizer/TimeStampItemNormalizerTraitDeprecatedTestClass.php
@@ -0,0 +1,14 @@
+<?php
+
+namespace Drupal\Tests\serialization\Unit\Normalizer;
+
+use Drupal\serialization\Normalizer\TimeStampItemNormalizerTrait;
+
+/**
+ * For testing that TimeStampItemNormalizerTrait throws a deprecation error.
+ *
+ * @see \Drupal\Tests\serialization\Unit\Normalizer\TimeStampItemNormalizerTraitDeprecatedTest
+ */
+class TimeStampItemNormalizerTraitDeprecatedTestClass {
+  use TimeStampItemNormalizerTrait;
+}