diff --git a/core/modules/simpletest/src/KernelTestBase.php b/core/modules/simpletest/src/KernelTestBase.php
index f953ed1..32d6ddc 100644
--- a/core/modules/simpletest/src/KernelTestBase.php
+++ b/core/modules/simpletest/src/KernelTestBase.php
@@ -171,7 +171,7 @@ protected function setUp() {
 
     // Re-inject extension file listings into state, unless the key/value
     // service was overridden (in which case its storage does not exist yet).
-    if (get_class($this->container->get('keyvalue')) === 'Drupal\Core\KeyValueStore\KeyValueMemoryFactory') {
+    if ($this->container->get('keyvalue') instanceof KeyValueMemoryFactory) {
       $this->container->get('state')->set('system.module.files', $this->moduleFiles);
       $this->container->get('state')->set('system.theme.files', $this->themeFiles);
     }
diff --git a/core/modules/system/src/Tests/Bootstrap/GetFilenameUnitTest.php b/core/modules/system/src/Tests/Bootstrap/GetFilenameUnitTest.php
index ba657c2..a7bcca7 100644
--- a/core/modules/system/src/Tests/Bootstrap/GetFilenameUnitTest.php
+++ b/core/modules/system/src/Tests/Bootstrap/GetFilenameUnitTest.php
@@ -7,8 +7,6 @@
 
 namespace Drupal\system\Tests\Bootstrap;
 
-use Drupal\Core\DependencyInjection\ContainerBuilder;
-use Drupal\Core\State\StateInterface;
 use Drupal\simpletest\KernelTestBase;
 
 /**
@@ -18,15 +16,10 @@
  */
 class GetFilenameUnitTest extends KernelTestBase {
 
-  /**
-   * {@inheritdoc}
-   */
-  public function containerBuild(ContainerBuilder $container) {
-    parent::containerBuild($container);
-
-    $container->set('state', NULL);
-    $container->getDefinition('state')
-      ->setClass(__NAMESPACE__ . '\NullState');
+  protected function setUp() {
+    parent::setUp();
+    $this->container = NULL;
+    \Drupal::setContainer(NULL);
   }
 
   /**
@@ -38,9 +31,9 @@ function testDrupalGetFilename() {
     global $install_state;
     $install_state['parameters']['profile'] = 'testing';
 
-    // Assert that the test is meaningful by making sure the state service
-    // always returns NULL.
-    $this->assertIdentical(get_class($this->container->get('state')), __NAMESPACE__ . '\NullState');
+    // Assert that this test is meaningful.
+    $this->assertNull($this->container);
+    $this->assertNull(\Drupal::getContainer());
 
     // Retrieving the location of a module.
     $this->assertIdentical(drupal_get_filename('module', 'system'), 'core/modules/system/system.info.yml');
@@ -59,33 +52,3 @@ function testDrupalGetFilename() {
     $this->assertNull(drupal_get_filename('module', uniqid("", TRUE)), 'Searching for an item that does not exist returns NULL.');
   }
 }
-
-/**
- * Stub State implementation; ignores all storage operations.
- */
-class NullState implements StateInterface {
-
-  public function get($key, $default = NULL) {
-    return $default;
-  }
-
-  public function getMultiple(array $keys) {
-    return array();
-  }
-
-  public function set($key, $value) {
-  }
-
-  public function setMultiple(array $data) {
-  }
-
-  public function delete($key) {
-  }
-
-  public function deleteMultiple(array $keys) {
-  }
-
-  public function resetCache() {
-  }
-
-}