diff --git a/core/modules/system/src/Tests/System/HtaccessTest.php b/core/modules/system/src/Tests/System/HtaccessTest.php
index c0a72c9..028956f 100644
--- a/core/modules/system/src/Tests/System/HtaccessTest.php
+++ b/core/modules/system/src/Tests/System/HtaccessTest.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\system\Tests\System;
 
-use Drupal\Core\Site\Settings;
 use Drupal\simpletest\WebTestBase;
 
 /**
@@ -18,12 +17,37 @@
 class HtaccessTest extends WebTestBase {
 
   /**
-   * Tests accessing disallowed file extensions.
+   * Modules to enable.
+   *
+   * @var array
    */
-  function testDisallowedExtensions() {
-    // Try accessing a yml file.
+  public static $modules = ['file'];
+
+  /**
+   * Tests accessing YAML file extensions.
+   */
+  public function testYamlFileAccess() {
+    // Try accessing the core services YAML file.
     $this->drupalGet('core/core.services.yml');
     $this->assertResponse(403);
+    // Try accessing a core module YAML file.
+    $this->drupalGet('core/modules/system/system.services.yml');
+    $this->assertResponse(403);
+
+    $file_params = array(
+      'filename' => 'test.yml',
+      'uri' => 'public://test.yml',
+      'filemime' => 'text/yaml',
+      'status' => FILE_STATUS_PERMANENT,
+    );
+    // Create a new file entity.
+    $file = entity_create('file', $file_params);
+    file_put_contents($file->getFileUri(), 'test: value');
+    $file->save();
+
+    // Access the file saved in the public files directory.
+    $this->drupalGet($file->url());
+    $this->assertResponse(200);
   }
 
 }