How to validate a config entity form?
You can override the validateForm method in your own form class. Just declare a method like so:

public function validateForm(array &amp;$form, FormStateInterface $form_state) {
  // Your custom validation code.
}


Since the Drupal\Core\Form\FormBase (parent of Drupal\Core\Entity\EntityForm) class has no validation, just a blank method, there is no need to call the parent method from your own class.