diff -u b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
--- b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
@@ -145,6 +145,11 @@
   protected $redirect_count;
 
   /**
+   * The kernel used in this test.
+   */
+  protected $kernel;
+
+  /**
    * Constructor for Drupal\simpletest\WebTestBase.
    */
   function __construct($test_id = NULL) {
@@ -658,10 +663,16 @@
     }
 
     // Create a new DrupalKernel for testing purposes, now that all required
-    // modules have been enabled.
-    $kernel = new DrupalKernel('testing', FALSE);
-    $kernel->boot();
-    $this->kernel = $kernel;
+    // modules have been enabled. This also stores a new dependency injection
+    // container in drupal_container(). Drupal\simpletest\TestBase::tearDown()
+    // restores the original container.
+    // @see Drupal\Core\DrupalKernel::initializeContainer()
+    $this->kernel = new DrupalKernel('testing', FALSE);
+    // While normally the kernel gets booted on demand in
+    // Symfony\Component\HttpKernel\handle() this kernel is only used to
+    // create a new dependency injection container and so it needs manual
+    // booting.
+    $this->kernel->boot();
 
     // Reset/rebuild all data structures after enabling the modules.
     $this->resetAll();