diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index 56e5f43..980d2cf 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -2412,7 +2412,7 @@ function drupal_container(Container $reset = NULL) {
   // which to reinitialize the stored objects, so a drupal_static_reset() call
   // would leave Drupal in a nonfunctional state.
   static $container = NULL;
-  if (isset($reset)) {
+  if (func_num_args()) {
     $container = $reset;
   }
   elseif (!isset($container)) {
diff --git a/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
index 25139e6..a6ffe62 100644
--- a/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
@@ -670,6 +670,8 @@ abstract class WebTestBase extends TestBase {
     // container in drupal_container(). Drupal\simpletest\TestBase::tearDown()
     // restores the original container.
     // @see Drupal\Core\DrupalKernel::initializeContainer()
+    drupal_container(NULL);
+    drupal_container();
     $this->kernel = new DrupalKernel('testing', FALSE);
     // Booting the kernel is necessary to initialize the new DIC. While
     // normally the kernel gets booted on demand in
diff --git a/core/scripts/run-tests.sh b/core/scripts/run-tests.sh
index 62107ab..c5eb216 100755
--- a/core/scripts/run-tests.sh
+++ b/core/scripts/run-tests.sh
@@ -479,7 +479,7 @@ function simpletest_script_cleanup($test_id, $test_class, $exitcode) {
     // simpletest_clean_temporary_directories() cannot be used here, since it
     // would also delete file directories of other tests that are potentially
     // running concurrently.
-    file_unmanaged_delete_recursive($test_directory);
+    file_unmanaged_delete_recursive($test_directory, array('Drupal\simpletest\TestBase', 'filePreDeleteCallback'));
     $messages[] = "- Removed test files directory.";
   }