TwigLoaderTest.php

<?php

declare (strict_types=1);
namespace Drupal\Tests\system\Kernel\Theme;

use Drupal\KernelTests\KernelTestBase;

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

}