Popsu-coloque/web/core/tests/Drupal/Tests/Core/Controller/TestController.php

<?php

namespace Drupal\Tests\Core\Controller;

use Symfony\Component\HttpFoundation\Response;

/**
 * Defines a test controller used by unit tests.
 */
class TestController {

  /**
   * Returns test content for unit tests.
   */
  public function content() {
    return new Response('');
  }

}