diff -u b/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
--- b/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
@@ -1157,7 +1157,7 @@
       $captured_emails = $state->get('system.test_mail_collector') ?: array();
       $emailCount = count($captured_emails);
       if ($emailCount) {
-        $message = $emailCount == 1 ? '1 e-mail was sent during this test.' : '@count e-mails were sent during this test.';
+        $message = $emailCount == 1 ? '1 e-mail was sent during this test.' : $emailCount . ' e-mails were sent during this test.';
         $this->pass($message, 'E-mail');
       }
     }