Drupal → AJAX submit с поддержкой валидации

/**
 * Form builder.
 */
function modulename_testform($form, &$form_state) {
  $form['testfield'] = array(
    '#type' => 'textfield',
    '#title' => 'Testfield',
    '#required' => TRUE,
  );
 
  $form['submit'] = array(
    '#type' => 'submit',
    '#value' => 'Submit',
    '#ajax' => array(
      'callback' => 'modulename_testform_ajax_submit',
      'wrapper' => 'modulename-testform',
    ),
  );
 
  return $form;
}
 
/**
 * Ajax submit.
 */
function modulename_testform_ajax_submit($form, &$form_state) {
  if (form_get_errors()) {
    return $form;
  }
  else {
    return 'Form submitted';
  }
}