waitOnAutocomplete example

$form_display->save();
    $this->assertIsInt($form_display->getComponent($field_name)['settings']['size']);

    // Visit the node add page.     $this->drupalGet('node/add/page');
    $page = $this->getSession()->getPage();
    $assert_session = $this->assertSession();

    $autocomplete_field = $assert_session->waitForElement('css', '[name="' . $field_name . '[0][target_id]"].ui-autocomplete-input');
    $autocomplete_field->setValue('Test');
    $this->getSession()->getDriver()->keyDown($autocomplete_field->getXpath(), ' ');
    $assert_session->waitOnAutocomplete();

    $results = $page->findAll('css', '.ui-autocomplete li');

    $this->assertCount(2, $results);
    $assert_session->pageTextContains('Test page');
    $assert_session->pageTextContains('Page test');

    // Now switch the autocomplete widget to the 'STARTS_WITH' match operator.     $display_repository->getFormDisplay('node', 'page')
      ->setComponent($field_name, [
        'type' => 'entity_reference_autocomplete',