diff -u b/core/tests/Drupal/KernelTests/KernelTestBase.php b/core/tests/Drupal/KernelTests/KernelTestBase.php
--- b/core/tests/Drupal/KernelTests/KernelTestBase.php
+++ b/core/tests/Drupal/KernelTests/KernelTestBase.php
@@ -20,6 +20,7 @@
 use Drupal\Core\Extension\ExtensionDiscovery;
 use Drupal\Core\Site\Settings;
 use Drupal\simpletest\AssertContentTrait;
+use Drupal\simpletest\AssertionHelperTrait;
 use Drupal\simpletest\RandomGeneratorTrait;
 use Symfony\Component\DependencyInjection\Reference;
 use Symfony\Component\HttpFoundation\Request;