Issue #3089961 by tim.plunkett, Deepak Goyal, Lal_, ravi.shankar, tedbow:...

   *

   * @param string $expected_form_id

   *   The expected form ID.

   * @param int $timeout

   *   (Optional) Timeout in milliseconds, defaults to 10000.

   */

  private function assertOffCanvasFormAfterWait($expected_form_id, $timeout = 10000) {

    $page = $this->getSession()->getPage();

  private function assertOffCanvasFormAfterWait($expected_form_id) {

    $this->assertSession()->assertWaitOnAjaxRequest();

    $this->assertNotEmpty($page->waitFor($timeout / 1000, function () use ($page, $expected_form_id) {

      // Ensure the form ID exists, is visible, and has the correct value.

      $form_id_element = $page->find('hidden_field_selector', ['hidden_field', 'form_id']);

      // Ensure the off canvas dialog is visible.

      $off_canvas = $page->find('css', '#drupal-off-canvas');

      if (!$off_canvas || !$off_canvas->isVisible()) {

        return NULL;

      }

      return $form_id_element;

    }));

    $off_canvas = $this->assertSession()->waitForElementVisible('css', '#drupal-off-canvas');

    $this->assertNotNull($off_canvas);

    $form_id_element = $off_canvas->find('hidden_field_selector', ['hidden_field', 'form_id']);

    // Ensure the form ID has the correct value and that the form is visible.

    $this->assertNotEmpty($form_id_element);

    $this->assertSame($expected_form_id, $form_id_element->getValue());

    $this->assertTrue($form_id_element->getParent()->isVisible());

  }

  /**