filter_formtest.module

<?php
/**
 * @file
 * Helper module for FilterEditorLinkValidateTestCase.
 */

/**
 * Implements hook_form_FORM_ID_alter().
 */
function filter_formtest_form_filter_format_editor_link_form_alter(&$form, &$form_state, $form_id) {
  $form['href']['#element_validate'][] = '_filter_formtest_href_element_validate';
}

/**
 * Helper function to output potentially altered form values as message.
 */
function _filter_formtest_href_element_validate(&$element, &$form_state) {
  if (isset($form_state['values'])) {
    $new_value = $form_state['values']['attributes']['href'];
    $message = format_string('Output href is: @href', array(
      '@href' => $new_value,
    ));
    backdrop_set_message($message, 'info');
  }
}