diff -u b/core/modules/user/tests/modules/user_hooks_test/user_hooks_test.module b/core/modules/user/tests/modules/user_hooks_test/user_hooks_test.module
--- b/core/modules/user/tests/modules/user_hooks_test/user_hooks_test.module
+++ b/core/modules/user/tests/modules/user_hooks_test/user_hooks_test.module
@@ -5,6 +5,8 @@
  * Support module for user hooks testing.
  */
 
+use Drupal\Core\Render\SafeString;
+
 /**
  * Implements hook_user_format_name_alter().
  */
@@ -12,7 +14,9 @@
   if (\Drupal::state()->get('user_hooks_test_user_format_name_alter', FALSE)) {
     if (\Drupal::state()->get('user_hooks_test_user_format_name_alter_safe', FALSE)) {
       // Make $name a SafeStringInterface object.
-      $name = t('<em>@id</em>', ['@id' => $account->id()]);
+      // @todo change this to SafeMarkup::format() after
+      //  https://www.drupal.org/node/2559971 lands.
+      $name = new SafeString('<em>@id</em>', ['@id' => $account->id()]);
     }
     else {
       $name = '<em>' . $account->id() . '</em>';