TestKernel.php

<?php

namespace Drupal\Core\Test;

use Drupal\Core\DrupalKernel;

/**
 * Kernel to mock requests to test simpletest.
 */
class TestKernel extends DrupalKernel {
    
    /**
     * {@inheritdoc}
     */
    public function __construct($environment, $class_loader, $allow_dumping = TRUE) {
        // Include our bootstrap file.
        require_once __DIR__ . '/../../../../includes/bootstrap.inc';
        // Exit if we should be in a test environment but aren't.
        if (!drupal_valid_test_ua()) {
            header($_SERVER['SERVER_PROTOCOL'] . ' 403 Forbidden');
            exit;
        }
        parent::__construct($environment, $class_loader, $allow_dumping);
    }

}