ElementsContainerTest.php

<?php

namespace Drupal\Tests\system\Functional\Form;

use Drupal\Tests\BrowserTestBase;

/**
 * Tests the container form element for expected behavior.
 *
 * @group Form
 */
class ElementsContainerTest extends BrowserTestBase {
    
    /**
     * Modules to enable.
     *
     * @var array
     */
    protected static $modules = [
        'form_test',
    ];
    
    /**
     * {@inheritdoc}
     */
    protected $defaultTheme = 'stark';
    
    /**
     * Tests the #optional container property.
     */
    public function testOptionalContainerElements() {
        $this->drupalGet('form-test/optional-container');
        $assertSession = $this->assertSession();
        $assertSession->elementNotExists('css', 'div.empty_optional');
        $assertSession->elementExists('css', 'div.empty_nonoptional');
        $assertSession->elementExists('css', 'div.nonempty_optional');
        $assertSession->elementExists('css', 'div.nonempty_nonoptional');
    }

}