ConfigEntityTest.php

<?php

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'));
    }

}