diff --git a/core/tests/Drupal/KernelTests/KernelTestBase.php b/core/tests/Drupal/KernelTests/KernelTestBase.php
index 64d267c..6012511 100644
--- a/core/tests/Drupal/KernelTests/KernelTestBase.php
+++ b/core/tests/Drupal/KernelTests/KernelTestBase.php
@@ -201,6 +201,13 @@ abstract class KernelTestBase extends \PHPUnit_Framework_TestCase implements Ser
     'config_test.dynamic.system',
   ];
 
+  /**
+   * The default list of directories that will be ignored by Drupal's file API.
+   *
+   * @var array
+   */
+  protected $ignoreDirectories = [];
+
   /**
    * {@inheritdoc}
    */
@@ -227,11 +234,32 @@ abstract class KernelTestBase extends \PHPUnit_Framework_TestCase implements Ser
     parent::setUp();
 
     $this->root = static::getDrupalRoot();
+    $this->backupIgnoreDirectories();
     $this->initFileCache();
     $this->bootEnvironment();
     $this->bootKernel();
   }
 
+  /**
+   * Backup "file_scan_ignore_directories" set in site's settings.php.
+   *
+   * @see \Drupal\KernelTests\KernelTestBase::getExtensionsForModules()
+   */
+  protected function backupIgnoreDirectories() {
+    /** @var $settings */
+    require_once $this->root . '/core/includes/bootstrap.inc';
+    $request = new Request();
+    $site_path = DrupalKernel::findSitePath($request);
+
+    if (file_exists($this->root . '/' . $site_path . '/settings.php')) {
+      $app_root = $this->root;
+      require_once $this->root . '/' . $site_path . '/settings.php';
+      if (isset($settings['file_scan_ignore_directories'])) {
+        $this->ignoreDirectories = $settings['file_scan_ignore_directories'];
+      }
+    }
+  }
+
   /**
    * Bootstraps a basic test environment.
    *
@@ -494,6 +522,11 @@ abstract class KernelTestBase extends \PHPUnit_Framework_TestCase implements Ser
    */
   private function getExtensionsForModules(array $modules) {
     $extensions = [];
+
+    $settings = Settings::getAll();
+    $settings['file_scan_ignore_directories'] = $this->ignoreDirectories;
+    new Settings($settings);
+
     $discovery = new ExtensionDiscovery($this->root);
     $discovery->setProfileDirectories([]);
     $list = $discovery->scan('module');