diff --git a/core/modules/contact/src/Plugin/Mail/HTMLTestingMailSystem.php b/core/lib/Drupal/Core/Mail/Plugin/Mail/HTMLTestMailCollector.php
similarity index 77%
rename from core/modules/contact/src/Plugin/Mail/HTMLTestingMailSystem.php
rename to core/lib/Drupal/Core/Mail/Plugin/Mail/HTMLTestMailCollector.php
index 32dd983..cfb0a18 100644
--- a/core/modules/contact/src/Plugin/Mail/HTMLTestingMailSystem.php
+++ b/core/lib/Drupal/Core/Mail/Plugin/Mail/HTMLTestMailCollector.php
@@ -1,10 +1,10 @@
 <?php
 /**
  * @file
- * Contains Drupal\contact\Plugin\Mail\HTMLTestingMailSystem.
+ * Contains \Drupal\Core\Mail\Plugin\Mail\HTMLTestMailCollector.
  */
 
-namespace Drupal\contact\Plugin\Mail;
+namespace Drupal\Core\Mail\Plugin\Mail;
 
 use Drupal\Core\Mail\MailFormatHelper;
 use Drupal\Core\Mail\MailInterface;
@@ -16,15 +16,15 @@
  * to plaintext.
  *
  * @Mail(
- *   id = "test_contact_html_mail",
+ *   id = "test_html_mail_collector",
  *   label = @Translation("HTML test mailer"),
  *   description = @Translation("Saves the message as HTML to a variable.")
  * )
  */
-class HTMLTestingMailSystem implements MailInterface {
+class HTMLTestMailCollector implements MailInterface {
 
   /**
-   * Implements MailSystemInterface::format().
+   * {@inheritdoc}
    */
   public function format(array $message) {
     // Join the body array into one string.
@@ -35,7 +35,7 @@ public function format(array $message) {
   }
 
   /**
-   * Implements MailSystemInterface::mail().
+   * {@inheritdoc}
    */
   public function mail(array $message) {
     $captured_emails = \Drupal::state()->get('system.test_mail_collector') ?: array();
diff --git a/core/modules/contact/src/Tests/ContactPersonalTest.php b/core/modules/contact/src/Tests/ContactPersonalTest.php
index faf8af2..e3abc4e 100644
--- a/core/modules/contact/src/Tests/ContactPersonalTest.php
+++ b/core/modules/contact/src/Tests/ContactPersonalTest.php
@@ -108,7 +108,7 @@ function testSendPersonalContactMessage() {
 
     // Use custom testing mail system to support HTML mails.
     $mail_config = $this->config('system.mail');
-    $mail_config->set('interface.default', 'test_contact_html_mail');
+    $mail_config->set('interface.default', 'test_html_mail_collector');
     $mail_config->save();
     // Test a subject that contains some common encoding characters.
     $variables = [