TwigLoaderTest.php

<?php

namespace Drupal\Tests\system\Functional\Theme;

use Drupal\Tests\BrowserTestBase;

/**
 * Tests adding Twig loaders.
 *
 * @group Theme
 */
class TwigLoaderTest extends BrowserTestBase {
    
    /**
     * Modules to enable.
     *
     * @var array
     */
    protected static $modules = [
        'twig_loader_test',
    ];
    
    /**
     * {@inheritdoc}
     */
    protected $defaultTheme = 'stark';
    
    /**
     * Tests adding an additional twig loader to the loader chain.
     */
    public function testTwigLoaderAddition() {
        $environment = \Drupal::service('twig');
        $template = $environment->loadTemplate('kittens');
        $this->assertEquals('kittens', $template->render([]), 'Passing "kittens" to the custom Twig loader returns "kittens".');
        $template = $environment->loadTemplate('meow');
        $this->assertEquals('cats', $template->render([]), 'Passing something other than "kittens" to the custom Twig loader returns "cats".');
    }

}