TestClass.php

<?php

namespace Drupal\service_provider_test;

use Drupal\Core\State\StateInterface;
use Drupal\Core\DestructableInterface;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpKernel\Event\ResponseEvent;
use Symfony\Component\HttpKernel\Event\RequestEvent;
use Symfony\Component\HttpKernel\KernelEvents;
class TestClass implements EventSubscriberInterface, DestructableInterface {

  /**
   * The state keyvalue collection.
   *
   * @var \Drupal\Core\State\StateInterface
   */
  protected $state;

  /**
   * Constructor.
   *
   * @param \Drupal\Core\State\StateInterface $state
   *   The state key value store.
   */
  public function __construct(StateInterface $state) {
    $this->state = $state;
  }

  /**
   * A simple kernel listener method.
   */
  public function onKernelRequestTest(RequestEvent $event) {
    \Drupal::messenger()
      ->addStatus(t('The service_provider_test event subscriber fired!'));
  }

  /**
   * Flags the response in case a rebuild indicator is used.
   */
  public function onKernelResponseTest(ResponseEvent $event) {
    $container = \Drupal::getContainer();
    if ($container
      ->hasParameter('container_rebuild_indicator')) {
      $event
        ->getResponse()->headers
        ->set('container_rebuild_indicator', $container
        ->getParameter('container_rebuild_indicator'));
    }
    if ($container
      ->hasParameter('container_rebuild_test_parameter')) {
      $event
        ->getResponse()->headers
        ->set('container_rebuild_test_parameter', $container
        ->getParameter('container_rebuild_test_parameter'));
    }
  }

  /**
   * Registers methods as kernel listeners.
   *
   * @return array
   *   An array of event listener definitions.
   */
  public static function getSubscribedEvents() : array {
    $events[KernelEvents::REQUEST][] = [
      'onKernelRequestTest',
    ];
    $events[KernelEvents::RESPONSE][] = [
      'onKernelResponseTest',
    ];
    return $events;
  }

  /**
   * {@inheritdoc}
   */
  public function destruct() {
    $this->state
      ->set('service_provider_test.destructed', TRUE);
  }

}