ConfigEntityTest.php

<?php

declare (strict_types=1);
namespace Drupal\Tests\config\FunctionalJavascript;

use Drupal\FunctionalJavascriptTests\WebDriverTestBase;

/**
 * Tests the Config operations through the UI.
 *
 * @group config
 */
class ConfigEntityTest extends WebDriverTestBase {

  /**
   * {@inheritdoc}
   */
  protected static $modules = [
    'config_test',
  ];

  /**
   * {@inheritdoc}
   */
  protected $defaultTheme = 'stark';

  /**
   * Tests ajax operations through the UI on 'Add' page.
   */
  public function testAjaxOnAddPage() {
    $this
      ->drupalLogin($this
      ->drupalCreateUser([
      'administer site configuration',
    ]));
    $page = $this
      ->getSession()
      ->getPage();
    $assert_session = $this
      ->assertSession();
    $this
      ->drupalGet('admin/structure/config_test/add');

    // Test that 'size value' field is not show initially, and it is show after
    // selecting value in the 'size' field.
    $this
      ->assertNull($page
      ->findField('size_value'));
    $page
      ->findField('size')
      ->setValue('custom');
    $this
      ->assertNotNull($assert_session
      ->waitForField('size_value'));
  }

}