diff -u b/core/lib/Drupal/Component/Datetime/TESTING.txt b/core/lib/Drupal/Component/Datetime/TESTING.txt
--- b/core/lib/Drupal/Component/Datetime/TESTING.txt
+++ b/core/lib/Drupal/Component/Datetime/TESTING.txt
@@ -19 +19 @@
-$ ./vendor/bin/phpunit --group Datetime
+$ ./vendor/bin/phpunit -c core --group Datetime
diff -u b/core/lib/Drupal/Component/Datetime/composer.json b/core/lib/Drupal/Component/Datetime/composer.json
--- b/core/lib/Drupal/Component/Datetime/composer.json
+++ b/core/lib/Drupal/Component/Datetime/composer.json
@@ -1,6 +1,6 @@
 {
   "name": "drupal/core-datetime",
-  "description": "Datetime.",
+  "description": "This class wraps the PHP DateTime class with more flexible initialization parameters, allowing a date to be created from an existing date object, a timestamp, a string with an unknown format, a string with a known format, or an array of date parts. It also adds an errors array and a __toString() method to the date object.",
   "keywords": ["drupal"],
   "homepage": "https://www.drupal.org/project/drupal",
   "license": "GPL-2.0+",
diff -u b/core/tests/Drupal/Tests/ComposerIntegrationTest.php b/core/tests/Drupal/Tests/ComposerIntegrationTest.php
--- b/core/tests/Drupal/Tests/ComposerIntegrationTest.php
+++ b/core/tests/Drupal/Tests/ComposerIntegrationTest.php
@@ -49,11 +49,11 @@
     return [
       $this->root,
       $this->root . '/core',
+      $this->root . '/core/lib/Drupal/Component/Datetime',
       $this->root . '/core/lib/Drupal/Component/Gettext',
       $this->root . '/core/lib/Drupal/Component/Plugin',
       $this->root . '/core/lib/Drupal/Component/ProxyBuilder',
       $this->root . '/core/lib/Drupal/Component/Utility',
-      $this->root . '/core/lib/Drupal/Component/Datetime',
     ];
   }