TestingExampleController.php

<?php

namespace Drupal\testing_example\Controller;

use Drupal\examples\Utility\DescriptionTemplateTrait;

/**
 * Controller for testing_example module.
 *
 * This class uses the DescriptionTemplateTrait to display text we put in the
 * templates/description.html.twig file.  We render out the text via its
 * description() method, and set up our routing to point to
 * TestingExampleController::description().
 */
class TestingExampleController {
    use DescriptionTemplateTrait;
    
    /**
     * {@inheritdoc}
     */
    protected function getModuleName() {
        return 'testing_example';
    }
    
    /**
     * Generate a render array for the Simpletest description.
     *
     * @return array
     *   A render array.
     */
    public function simpletestDescription() {
        $template_file = \Drupal::service('extension.list.module')->getPath('testing_example') . '/templates/simpletest.description.html.twig';
        $build = [
            'description' => [
                '#type' => 'inline_template',
                '#template' => file_get_contents($template_file),
            ],
        ];
        return $build;
    }

}