TestKernel.php

<?php

namespace Drupal\Core\Test;

use Drupal\Core\DependencyInjection\ContainerBuilder;
use Drupal\Component\DependencyInjection\ReverseContainer;
use Drupal\Core\DrupalKernel;

/**
 * Kernel that is only used by mock front controllers.
 */
class TestKernel extends DrupalKernel {
    
    /**
     * {@inheritdoc}
     */
    public function __construct($environment, $class_loader, $allow_dumping = TRUE) {
        // Exit if we should be in a test environment but aren't.
        if (!drupal_valid_test_ua()) {
            header($_SERVER['SERVER_PROTOCOL'] . ' 403 Forbidden');
            exit;
        }
        parent::__construct($environment, $class_loader, $allow_dumping);
    }
    
    /**
     * Sets a container with a kernel service on the Drupal class.
     *
     * @return \Drupal\Component\DependencyInjection\ContainerInterface
     *   A container with the kernel service set.
     */
    public static function setContainerWithKernel() {
        $container = new ContainerBuilder();
        $kernel = new DrupalKernel('test', NULL);
        // Objects of the same type will have access to each others private and
        // protected members even though they are not the same instances. This is
        // because the implementation specific details are already known when
        // inside those objects.
        $kernel->container = $container;
        $container->set('kernel', $kernel);
        $container->set(ReverseContainer::class, new ReverseContainer($container));
        \Drupal::setContainer($container);
        return $container;
    }

}