diff -u b/core/lib/Drupal/Core/Form/FormBuilder.php b/core/lib/Drupal/Core/Form/FormBuilder.php
--- b/core/lib/Drupal/Core/Form/FormBuilder.php
+++ b/core/lib/Drupal/Core/Form/FormBuilder.php
@@ -790,6 +790,7 @@
         '#type' => 'hidden',
         '#value' => $form_id,
         '#id' => Html::getUniqueId("edit-$form_id"),
+        '#attributes' => ['data-drupal-selector' => Html::getId("edit-$form_id")],
         // Form processing and validation requires this value, so ensure the
         // submitted form value appears literally, regardless of custom #tree
         // and #parents being set elsewhere.