TwigEnvironmentTest.php

<?php

namespace Drupal\Tests\system\Functional\Theme;

use Drupal\Tests\BrowserTestBase;

/**
 * Tests Twig environment.
 *
 * @group Theme
 */
class TwigEnvironmentTest extends BrowserTestBase {
    
    /**
     * {@inheritdoc}
     */
    protected static $modules = [
        'twig_theme_test',
    ];
    
    /**
     * {@inheritdoc}
     */
    protected $defaultTheme = 'stark';
    
    /**
     * Tests template class loading with Twig embed.
     */
    public function testTwigEmbed() {
        $assert_session = $this->assertSession();
        // Test the Twig embed tag.
        $this->drupalGet('twig-theme-test/embed-tag');
        $assert_session->statusCodeEquals(200);
        $assert_session->responseContains('This line is from twig_theme_test/templates/twig-theme-test-embed-tag-embedded.html.twig');
    }

}