diff --git a/core/includes/file.inc b/core/includes/file.inc
index 545fca3..c487b81 100644
--- a/core/includes/file.inc
+++ b/core/includes/file.inc
@@ -191,12 +191,16 @@ function file_get_stream_wrappers($filter = STREAM_WRAPPERS_ALL) {
   $wrappers_storage = &drupal_static(__FUNCTION__);
 
   if (!isset($wrappers_storage)) {
-    $wrappers = \Drupal::moduleHandler()->invokeAll('stream_wrappers');
-    foreach ($wrappers as $scheme => $info) {
-      // Add defaults.
-      $wrappers[$scheme] += array('type' => STREAM_WRAPPERS_NORMAL);
+    $wrappers = array();
+    $container = \Drupal::getContainer();
+    if (is_object($container) && $container->has('module_handler')) {
+      $wrappers = \Drupal::moduleHandler()->invokeAll('stream_wrappers');
+      foreach ($wrappers as $scheme => $info) {
+        // Add defaults.
+        $wrappers[$scheme] += array('type' => STREAM_WRAPPERS_NORMAL);
+      }
+      drupal_alter('stream_wrappers', $wrappers);
     }
-    drupal_alter('stream_wrappers', $wrappers);
     $existing = stream_get_wrappers();
     foreach ($wrappers as $scheme => $info) {
       // We only register classes that implement our interface.
diff --git a/core/modules/file/lib/Drupal/file/Tests/CopyTest.php b/core/modules/file/lib/Drupal/file/Tests/CopyTest.php
index 1c0dce6..6ee9c99 100644
--- a/core/modules/file/lib/Drupal/file/Tests/CopyTest.php
+++ b/core/modules/file/lib/Drupal/file/Tests/CopyTest.php
@@ -15,7 +15,7 @@ public static function getInfo() {
     return array(
       'name' => 'File copying',
       'description' => 'Tests the file copy function.',
-      'group' => 'File API',
+      'group' => 'File Managed API',
     );
   }
 
diff --git a/core/modules/file/lib/Drupal/file/Tests/DeleteTest.php b/core/modules/file/lib/Drupal/file/Tests/DeleteTest.php
index 9d1911b..f65e905 100644
--- a/core/modules/file/lib/Drupal/file/Tests/DeleteTest.php
+++ b/core/modules/file/lib/Drupal/file/Tests/DeleteTest.php
@@ -15,7 +15,7 @@ public static function getInfo() {
     return array(
       'name' => 'File delete',
       'description' => 'Tests the file delete function.',
-      'group' => 'File API',
+      'group' => 'File Managed API',
     );
   }
 
diff --git a/core/modules/file/lib/Drupal/file/Tests/DownloadTest.php b/core/modules/file/lib/Drupal/file/Tests/DownloadTest.php
index 1870fe7..e39b39c 100644
--- a/core/modules/file/lib/Drupal/file/Tests/DownloadTest.php
+++ b/core/modules/file/lib/Drupal/file/Tests/DownloadTest.php
@@ -17,7 +17,7 @@ public static function getInfo() {
     return array(
       'name' => 'File download',
       'description' => 'Tests for file download/transfer functions.',
-      'group' => 'File API',
+      'group' => 'File Managed API',
     );
   }
 
diff --git a/core/modules/file/lib/Drupal/file/Tests/FileManagedTestBase.php b/core/modules/file/lib/Drupal/file/Tests/FileManagedTestBase.php
index 85ee553..b4c70c3 100644
--- a/core/modules/file/lib/Drupal/file/Tests/FileManagedTestBase.php
+++ b/core/modules/file/lib/Drupal/file/Tests/FileManagedTestBase.php
@@ -7,14 +7,14 @@
 
 namespace Drupal\file\Tests;
 
-use Drupal\system\Tests\File\FileTestBase;
-use \stdClass;
+use Drupal\file\FileInterface;
+use Drupal\simpletest\WebTestBase;
 
 /**
  * Base class for file tests that use the file_test module to test uploads and
  * hooks.
  */
-abstract class FileManagedTestBase extends FileTestBase {
+abstract class FileManagedTestBase extends WebTestBase {
 
   /**
    * Modules to enable.
@@ -90,6 +90,50 @@ function assertFileHookCalled($hook, $expected_count = 1, $message = NULL) {
   }
 
   /**
+   * Asserts that two files have the same values (except timestamp).
+   *
+   * @param \Drupal\file\FileInterface $before
+   *   File object to compare.
+   * @param \Drupal\file\FileInterface $after
+   *   File object to compare.
+   */
+  function assertFileUnchanged(FileInterface $before, FileInterface $after) {
+    $this->assertEqual($before->id(), $after->id(), t('File id is the same: %file1 == %file2.', array('%file1' => $before->id(), '%file2' => $after->id())), 'File unchanged');
+    $this->assertEqual($before->getOwner()->id(), $after->getOwner()->id(), t('File owner is the same: %file1 == %file2.', array('%file1' => $before->getOwner()->id(), '%file2' => $after->getOwner()->id())), 'File unchanged');
+    $this->assertEqual($before->getFilename(), $after->getFilename(), t('File name is the same: %file1 == %file2.', array('%file1' => $before->getFilename(), '%file2' => $after->getFilename())), 'File unchanged');
+    $this->assertEqual($before->getFileUri(), $after->getFileUri(), t('File path is the same: %file1 == %file2.', array('%file1' => $before->getFileUri(), '%file2' => $after->getFileUri())), 'File unchanged');
+    $this->assertEqual($before->getMimeType(), $after->getMimeType(), t('File MIME type is the same: %file1 == %file2.', array('%file1' => $before->getMimeType(), '%file2' => $after->getMimeType())), 'File unchanged');
+    $this->assertEqual($before->getSize(), $after->getSize(), t('File size is the same: %file1 == %file2.', array('%file1' => $before->getSize(), '%file2' => $after->getSize())), 'File unchanged');
+    $this->assertEqual($before->isPermanent(), $after->isPermanent(), t('File status is the same: %file1 == %file2.', array('%file1' => $before->isPermanent(), '%file2' => $after->isPermanent())), 'File unchanged');
+  }
+
+  /**
+   * Asserts that two files are not the same by comparing the fid and filepath.
+   *
+   * @param \Drupal\file\FileInterface $file1
+   *   File object to compare.
+   * @param \Drupal\file\FileInterface $file2
+   *   File object to compare.
+   */
+  function assertDifferentFile(FileInterface $file1, FileInterface $file2) {
+    $this->assertNotEqual($file1->id(), $file2->id(), t('Files have different ids: %file1 != %file2.', array('%file1' => $file1->id(), '%file2' => $file2->id())), 'Different file');
+    $this->assertNotEqual($file1->getFileUri(), $file2->getFileUri(), t('Files have different paths: %file1 != %file2.', array('%file1' => $file1->getFileUri(), '%file2' => $file2->getFileUri())), 'Different file');
+  }
+
+  /**
+   * Asserts that two files are the same by comparing the fid and filepath.
+   *
+   * @param \Drupal\file\FileInterface $file1
+   *   File object to compare.
+   * @param \Drupal\file\FileInterface $file2
+   *   File object to compare.
+   */
+  function assertSameFile(FileInterface $file1, FileInterface $file2) {
+    $this->assertEqual($file1->id(), $file2->id(), t('Files have the same ids: %file1 == %file2.', array('%file1' => $file1->id(), '%file2-fid' => $file2->id())), 'Same file');
+    $this->assertEqual($file1->getFileUri(), $file2->getFileUri(), t('Files have the same path: %file1 == %file2.', array('%file1' => $file1->getFileUri(), '%file2' => $file2->getFileUri())), 'Same file');
+  }
+
+  /**
    * Create a file and save it to the files table and assert that it occurs
    * correctly.
    *
@@ -106,7 +150,7 @@ function assertFileHookCalled($hook, $expected_count = 1, $message = NULL) {
    *   File entity.
    */
   function createFile($filepath = NULL, $contents = NULL, $scheme = NULL) {
-    $file = new stdClass();
+    $file = new \stdClass();
     $file->uri = $this->createUri($filepath, $contents, $scheme);
     $file->filename = drupal_basename($file->uri);
     $file->filemime = 'text/plain';
@@ -121,4 +165,41 @@ function createFile($filepath = NULL, $contents = NULL, $scheme = NULL) {
 
     return entity_create('file', (array) $file);
   }
+
+  /**
+   * Creates a file and returns its URI.
+   *
+   * @param string $filepath
+   *   Optional string specifying the file path. If none is provided then a
+   *   randomly named file will be created in the site's files directory.
+   * @param string $contents
+   *   Optional contents to save into the file. If a NULL value is provided an
+   *   arbitrary string will be used.
+   * @param string $scheme
+   *   Optional string indicating the stream scheme to use. Drupal core includes
+   *   public, private, and temporary. The public wrapper is the default.
+   *
+   * @return string
+   *   File URI.
+   */
+  function createUri($filepath = NULL, $contents = NULL, $scheme = NULL) {
+    if (!isset($filepath)) {
+      // Prefix with non-latin characters to ensure that all file-related
+      // tests work with international filenames.
+      $filepath = 'Файл для тестирования ' . $this->randomName();
+    }
+    if (!isset($scheme)) {
+      $scheme = file_default_scheme();
+    }
+    $filepath = $scheme . '://' . $filepath;
+
+    if (!isset($contents)) {
+      $contents = "file_put_contents() doesn't seem to appreciate empty strings so let's put in some data.";
+    }
+
+    file_put_contents($filepath, $contents);
+    $this->assertTrue(is_file($filepath), t('The test file exists on the disk.'), 'Create test file');
+    return $filepath;
+  }
+
 }
diff --git a/core/modules/file/lib/Drupal/file/Tests/LoadTest.php b/core/modules/file/lib/Drupal/file/Tests/LoadTest.php
index 0199ea2..6a85e83 100644
--- a/core/modules/file/lib/Drupal/file/Tests/LoadTest.php
+++ b/core/modules/file/lib/Drupal/file/Tests/LoadTest.php
@@ -15,7 +15,7 @@ public static function getInfo() {
     return array(
       'name' => 'File loading',
       'description' => 'Tests the file_load() function.',
-      'group' => 'File API',
+      'group' => 'File Managed API',
     );
   }
 
diff --git a/core/modules/file/lib/Drupal/file/Tests/MoveTest.php b/core/modules/file/lib/Drupal/file/Tests/MoveTest.php
index 5037af0..8fb7b07 100644
--- a/core/modules/file/lib/Drupal/file/Tests/MoveTest.php
+++ b/core/modules/file/lib/Drupal/file/Tests/MoveTest.php
@@ -15,7 +15,7 @@ public static function getInfo() {
     return array(
       'name' => 'File moving',
       'description' => 'Tests the file move function.',
-      'group' => 'File API',
+      'group' => 'File Managed API',
     );
   }
 
diff --git a/core/modules/file/lib/Drupal/file/Tests/RemoteFileSaveUploadTest.php b/core/modules/file/lib/Drupal/file/Tests/RemoteFileSaveUploadTest.php
index b9932b7..6f2000c 100644
--- a/core/modules/file/lib/Drupal/file/Tests/RemoteFileSaveUploadTest.php
+++ b/core/modules/file/lib/Drupal/file/Tests/RemoteFileSaveUploadTest.php
@@ -21,7 +21,7 @@ class RemoteFileSaveUploadTest extends SaveUploadTest {
 
   public static function getInfo() {
     $info = parent::getInfo();
-    $info['group'] = 'File API (remote)';
+    $info['group'] = 'File Managed API (remote)';
     return $info;
   }
 
diff --git a/core/modules/file/lib/Drupal/file/Tests/SaveDataTest.php b/core/modules/file/lib/Drupal/file/Tests/SaveDataTest.php
index 5579baf..9b1bf2a 100644
--- a/core/modules/file/lib/Drupal/file/Tests/SaveDataTest.php
+++ b/core/modules/file/lib/Drupal/file/Tests/SaveDataTest.php
@@ -15,7 +15,7 @@ public static function getInfo() {
     return array(
       'name' => 'File save data',
       'description' => 'Tests the file save data function.',
-      'group' => 'File API',
+      'group' => 'File Managed API',
     );
   }
 
diff --git a/core/modules/file/lib/Drupal/file/Tests/SaveTest.php b/core/modules/file/lib/Drupal/file/Tests/SaveTest.php
index 4c3b0c0..c2f0c38 100644
--- a/core/modules/file/lib/Drupal/file/Tests/SaveTest.php
+++ b/core/modules/file/lib/Drupal/file/Tests/SaveTest.php
@@ -17,7 +17,7 @@ public static function getInfo() {
     return array(
       'name' => 'File saving',
       'description' => 'File saving tests',
-      'group' => 'File API',
+      'group' => 'File Managed API',
     );
   }
 
diff --git a/core/modules/file/lib/Drupal/file/Tests/SaveUploadTest.php b/core/modules/file/lib/Drupal/file/Tests/SaveUploadTest.php
index 15e007b..d9b570f 100644
--- a/core/modules/file/lib/Drupal/file/Tests/SaveUploadTest.php
+++ b/core/modules/file/lib/Drupal/file/Tests/SaveUploadTest.php
@@ -30,7 +30,7 @@ public static function getInfo() {
     return array(
       'name' => 'File uploading',
       'description' => 'Tests the file uploading functions.',
-      'group' => 'File API',
+      'group' => 'File Managed API',
     );
   }
 
diff --git a/core/modules/file/lib/Drupal/file/Tests/SpaceUsedTest.php b/core/modules/file/lib/Drupal/file/Tests/SpaceUsedTest.php
index 4925cbf..b98134b 100644
--- a/core/modules/file/lib/Drupal/file/Tests/SpaceUsedTest.php
+++ b/core/modules/file/lib/Drupal/file/Tests/SpaceUsedTest.php
@@ -15,7 +15,7 @@ public static function getInfo() {
     return array(
       'name' => 'File space used tests',
       'description' => 'Tests the spaceUsed() function.',
-      'group' => 'File API',
+      'group' => 'File Managed API',
     );
   }
 
diff --git a/core/modules/file/lib/Drupal/file/Tests/UsageTest.php b/core/modules/file/lib/Drupal/file/Tests/UsageTest.php
index 5ce7937..713cc33 100644
--- a/core/modules/file/lib/Drupal/file/Tests/UsageTest.php
+++ b/core/modules/file/lib/Drupal/file/Tests/UsageTest.php
@@ -15,7 +15,7 @@ public static function getInfo() {
     return array(
       'name' => 'File usage',
       'description' => 'Tests the file usage functions.',
-      'group' => 'File API',
+      'group' => 'File Managed API',
     );
   }
 
diff --git a/core/modules/file/lib/Drupal/file/Tests/ValidateTest.php b/core/modules/file/lib/Drupal/file/Tests/ValidateTest.php
index faef73f..5656fdc 100644
--- a/core/modules/file/lib/Drupal/file/Tests/ValidateTest.php
+++ b/core/modules/file/lib/Drupal/file/Tests/ValidateTest.php
@@ -15,7 +15,7 @@ public static function getInfo() {
     return array(
       'name' => 'File validate',
       'description' => 'Tests the file_validate() function.',
-      'group' => 'File API',
+      'group' => 'File Managed API',
     );
   }
 
diff --git a/core/modules/file/lib/Drupal/file/Tests/ValidatorTest.php b/core/modules/file/lib/Drupal/file/Tests/ValidatorTest.php
index cfde9a3..62b51fb 100644
--- a/core/modules/file/lib/Drupal/file/Tests/ValidatorTest.php
+++ b/core/modules/file/lib/Drupal/file/Tests/ValidatorTest.php
@@ -15,7 +15,7 @@ public static function getInfo() {
     return array(
       'name' => 'File validator tests',
       'description' => 'Tests the functions used to validate uploaded files.',
-      'group' => 'File API',
+      'group' => 'File Managed API',
     );
   }
 
diff --git a/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php
index b7848de..f4738fa 100644
--- a/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php
@@ -64,6 +64,15 @@
   protected $keyValueFactory;
 
   /**
+   * A list of stream wrappers that have been registered for this test.
+   *
+   * @see \Drupal\simpletest\DrupalUnitTestBase::registerStreamWrapper()
+   *
+   * @var array
+   */
+  private $streamWrappers = array();
+
+  /**
    * Overrides \Drupal\simpletest\UnitTestBase::__construct().
    */
   function __construct($test_id = NULL) {
@@ -88,6 +97,7 @@ protected function setUp() {
     $this->keyValueFactory = new KeyValueMemoryFactory();
 
     parent::setUp();
+
     // Build a minimal, partially mocked environment for unit tests.
     $this->containerBuild(\Drupal::getContainer());
     // Make sure it survives kernel rebuilds.
@@ -130,10 +140,28 @@ protected function setUp() {
     $this->enableModules($modules, FALSE);
     // In order to use theme functions default theme config needs to exist.
     \Drupal::config('system.theme')->set('default', 'stark');
+
+    // Tests based on DrupalUnitTestBase are entitled to use Drupal's File API.
+    $this->registerStreamWrapper('public', 'Drupal\Core\StreamWrapper\PublicStream');
+
+    // The private and temporary stream wrappers depend on the system.file
+    // configuration. If System module was enabled, the test will most likely
+    // install System module's configuration, so we can register them here.
+    if (in_array('system', $modules)) {
+      $this->registerStreamWrapper('private', 'Drupal\Core\StreamWrapper\PrivateStream');
+      $this->registerStreamWrapper('temporary', 'Drupal\Core\StreamWrapper\TemporaryStream');
+    }
   }
 
   protected function tearDown() {
     $this->kernel->shutdown();
+    // Before tearing down the test environment, ensure that no stream wrapper
+    // of this test leaks into the parent environment. Unlike all other global
+    // state variables in Drupal, stream wrappers are a global state construct
+    // of PHP core, which has to be maintained manually.
+    foreach ($this->streamWrappers as $scheme) {
+      $this->unregisterStreamWrapper($scheme);
+    }
     parent::tearDown();
   }
 
@@ -334,4 +362,53 @@ protected function disableModules(array $modules) {
     )));
   }
 
+  /**
+   * Registers a stream wrapper for this test.
+   *
+   * @param string $scheme
+   *   The scheme to register.
+   * @param string $class
+   *   The fully qualified class name to register.
+   * @param int $type
+   *   The Drupal Stream Wrapper API type. Defaults to
+   *   STREAM_WRAPPERS_LOCAL_NORMAL.
+   */
+  protected function registerStreamWrapper($scheme, $class, $type = STREAM_WRAPPERS_LOCAL_NORMAL) {
+    if (isset($this->streamWrappers[$scheme])) {
+      $this->unregisterStreamWrapper($scheme);
+    }
+    $this->streamWrappers[$scheme] = $scheme;
+    if (($type & STREAM_WRAPPERS_LOCAL) == STREAM_WRAPPERS_LOCAL) {
+      stream_wrapper_register($scheme, $class);
+    }
+    else {
+      stream_wrapper_register($scheme, $class, STREAM_IS_URL);
+    }
+    // @todo Revamp Drupal's stream wrapper API for D8.
+    $wrappers = &drupal_static('file_get_stream_wrappers');
+    $wrappers[$scheme] = array(
+      'type' => $type,
+      'class' => $class,
+    );
+    $wrappers[STREAM_WRAPPERS_ALL] = $wrappers;
+  }
+
+  /**
+   * Unregisters a stream wrapper previously registered by this test.
+   *
+   * DrupalUnitTestBase::tearDown() automatically cleans up all registered
+   * stream wrappers, so this usually does not have to be called manually.
+   *
+   * @param string $scheme
+   *   The scheme to unregister.
+   */
+  protected function unregisterStreamWrapper($scheme) {
+    stream_wrapper_unregister($scheme);
+    unset($this->streamWrappers[$scheme]);
+    // @todo Revamp Drupal's stream wrapper API for D8.
+    $wrappers = &drupal_static('file_get_stream_wrappers');
+    unset($wrappers[$scheme]);
+    unset($wrappers[STREAM_WRAPPERS_ALL][$scheme]);
+  }
+
 }
diff --git a/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
index 669c615..dbf8440 100644
--- a/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
@@ -963,6 +963,19 @@ protected function prepareEnvironment() {
     // Create and set new configuration directories.
     $this->prepareConfigDirectories();
 
+    // Unregister all custom stream wrappers of the parent site.
+    // Availability of Drupal stream wrappers varies by test base class:
+    // - UnitTestBase operates in a completely empty environment.
+    // - DrupalUnitTestBase supports and maintains stream wrappers in a custom
+    //   way.
+    // - WebTestBase re-initializes Drupal stream wrappers after installation.
+    // The original stream wrappers are restored after the test run.
+    // @see TestBase::tearDown()
+    $wrappers = file_get_stream_wrappers();
+    foreach ($wrappers as $scheme => $info) {
+      stream_wrapper_unregister($scheme);
+    }
+
     // Reset statics before the old container is replaced so that objects with a
     // __destruct() method still have access to it.
     // @todo: Remove once they have been converted to services.
@@ -1106,10 +1119,6 @@ protected function tearDown() {
       }
     }
 
-    // In case a fatal error occurred that was not in the test process read the
-    // log to pick up any fatal errors.
-    simpletest_log_read($this->testId, $this->databasePrefix, get_class($this), TRUE);
-
     // Delete temporary files directory.
     file_unmanaged_delete_recursive($this->originalFileDirectory . '/simpletest/' . substr($this->databasePrefix, 10), array($this, 'filePreDeleteCallback'));
 
@@ -1139,6 +1148,17 @@ protected function tearDown() {
     // Restore original statics and globals.
     \Drupal::setContainer($this->originalContainer);
     $GLOBALS['config_directories'] = $this->originalConfigDirectories;
+
+    // Re-initialize original stream wrappers of the parent site.
+    // This must happen after static variables have been reset and the original
+    // container and $config_directories are restored, as simpletest_log_read()
+    // uses the public stream wrapper to locate the error.log.
+    file_get_stream_wrappers();
+
+    // In case a fatal error occurred that was not in the test process read the
+    // log to pick up any fatal errors.
+    simpletest_log_read($this->testId, $this->databasePrefix, get_class($this), TRUE);
+
     if (isset($this->originalPrefix)) {
       drupal_valid_test_ua($this->originalPrefix);
     }
diff --git a/core/modules/system/lib/Drupal/system/Tests/File/ConfigTest.php b/core/modules/system/lib/Drupal/system/Tests/File/ConfigTest.php
index ce48dfd..a38322b 100644
--- a/core/modules/system/lib/Drupal/system/Tests/File/ConfigTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/File/ConfigTest.php
@@ -7,10 +7,12 @@
 
 namespace Drupal\system\Tests\File;
 
+use Drupal\simpletest\WebTestBase;
+
 /**
  * File system configuration related tests.
  */
-class ConfigTest extends FileTestBase {
+class ConfigTest extends WebTestBase {
 
   public static function getInfo() {
     return array(
diff --git a/core/modules/system/lib/Drupal/system/Tests/File/FileTestBase.php b/core/modules/system/lib/Drupal/system/Tests/File/FileTestBase.php
index 540c19a..2071ced 100644
--- a/core/modules/system/lib/Drupal/system/Tests/File/FileTestBase.php
+++ b/core/modules/system/lib/Drupal/system/Tests/File/FileTestBase.php
@@ -7,68 +7,28 @@
 
 namespace Drupal\system\Tests\File;
 
-use Drupal\file\FileInterface;
-use Drupal\simpletest\WebTestBase;
+use Drupal\simpletest\DrupalUnitTestBase;
 
 /**
  * Base class for file tests that adds some additional file specific
  * assertions and helper functions.
  */
-abstract class FileTestBase extends WebTestBase {
-
-  function setUp() {
-    parent::setUp();
-    // Make sure that custom stream wrappers are registered.
-    // @todo This has the potential to be a major bug deeply buried in File API;
-    //   file_unmanaged_*() API functions and test functions are invoking native
-    //   PHP functions directly, whereas Drupal's custom stream wrappers are not
-    //   registered yet.
-    file_get_stream_wrappers();
-  }
+abstract class FileTestBase extends DrupalUnitTestBase {
 
   /**
-   * Check that two files have the same values for all fields other than the
-   * timestamp.
+   * Modules to enable.
    *
-   * @param \Drupal\file\FileInterface $before
-   *   File object to compare.
-   * @param \Drupal\file\FileInterface $after
-   *   File object to compare.
+   * @var array
    */
-  function assertFileUnchanged(FileInterface $before, FileInterface $after) {
-    $this->assertEqual($before->id(), $after->id(), t('File id is the same: %file1 == %file2.', array('%file1' => $before->id(), '%file2' => $after->id())), 'File unchanged');
-    $this->assertEqual($before->getOwner()->id(), $after->getOwner()->id(), t('File owner is the same: %file1 == %file2.', array('%file1' => $before->getOwner()->id(), '%file2' => $after->getOwner()->id())), 'File unchanged');
-    $this->assertEqual($before->getFilename(), $after->getFilename(), t('File name is the same: %file1 == %file2.', array('%file1' => $before->getFilename(), '%file2' => $after->getFilename())), 'File unchanged');
-    $this->assertEqual($before->getFileUri(), $after->getFileUri(), t('File path is the same: %file1 == %file2.', array('%file1' => $before->getFileUri(), '%file2' => $after->getFileUri())), 'File unchanged');
-    $this->assertEqual($before->getMimeType(), $after->getMimeType(), t('File MIME type is the same: %file1 == %file2.', array('%file1' => $before->getMimeType(), '%file2' => $after->getMimeType())), 'File unchanged');
-    $this->assertEqual($before->getSize(), $after->getSize(), t('File size is the same: %file1 == %file2.', array('%file1' => $before->getSize(), '%file2' => $after->getSize())), 'File unchanged');
-    $this->assertEqual($before->isPermanent(), $after->isPermanent(), t('File status is the same: %file1 == %file2.', array('%file1' => $before->isPermanent(), '%file2' => $after->isPermanent())), 'File unchanged');
-  }
+  public static $modules = array('system');
 
-  /**
-   * Check that two files are not the same by comparing the fid and filepath.
-   *
-   * @param \Drupal\file\FileInterface $file1
-   *   File object to compare.
-   * @param \Drupal\file\FileInterface $file2
-   *   File object to compare.
-   */
-  function assertDifferentFile(FileInterface $file1, FileInterface $file2) {
-    $this->assertNotEqual($file1->id(), $file2->id(), t('Files have different ids: %file1 != %file2.', array('%file1' => $file1->id(), '%file2' => $file2->id())), 'Different file');
-    $this->assertNotEqual($file1->getFileUri(), $file2->getFileUri(), t('Files have different paths: %file1 != %file2.', array('%file1' => $file1->getFileUri(), '%file2' => $file2->getFileUri())), 'Different file');
-  }
+  function setUp() {
+    parent::setUp();
+    $this->installConfig(array('system'));
 
-  /**
-   * Check that two files are the same by comparing the fid and filepath.
-   *
-   * @param \Drupal\file\FileInterface $file1
-   *   File object to compare.
-   * @param \Drupal\file\FileInterface $file2
-   *   File object to compare.
-   */
-  function assertSameFile(FileInterface $file1, FileInterface $file2) {
-    $this->assertEqual($file1->id(), $file2->id(), t('Files have the same ids: %file1 == %file2.', array('%file1' => $file1->id(), '%file2-fid' => $file2->id())), 'Same file');
-    $this->assertEqual($file1->getFileUri(), $file2->getFileUri(), t('Files have the same path: %file1 == %file2.', array('%file1' => $file1->getFileUri(), '%file2' => $file2->getFileUri())), 'Same file');
+    if (isset($this->scheme)) {
+      $this->registerStreamWrapper($this->scheme, $this->classname);
+    }
   }
 
   /**
@@ -170,7 +130,7 @@ function createDirectory($path = NULL) {
     return $path;
   }
 
-    /**
+  /**
    * Create a file and return the URI of it.
    *
    * @param $filepath
diff --git a/core/modules/system/lib/Drupal/system/Tests/File/MimeTypeTest.php b/core/modules/system/lib/Drupal/system/Tests/File/MimeTypeTest.php
index 5ee981d..e9c388d 100644
--- a/core/modules/system/lib/Drupal/system/Tests/File/MimeTypeTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/File/MimeTypeTest.php
@@ -7,12 +7,10 @@
 
 namespace Drupal\system\Tests\File;
 
-use Drupal\simpletest\WebTestBase;
-
 /**
  * Tests for file_get_mimetype().
  */
-class MimeTypeTest extends WebTestBase {
+class MimeTypeTest extends FileTestBase {
 
   /**
    * Modules to enable.
diff --git a/core/modules/system/lib/Drupal/system/Tests/File/ReadOnlyStreamWrapperTest.php b/core/modules/system/lib/Drupal/system/Tests/File/ReadOnlyStreamWrapperTest.php
index ef84796..779ba12 100644
--- a/core/modules/system/lib/Drupal/system/Tests/File/ReadOnlyStreamWrapperTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/File/ReadOnlyStreamWrapperTest.php
@@ -12,13 +12,6 @@
  */
 class ReadOnlyStreamWrapperTest extends FileTestBase {
 
-  /**
-   * Modules to enable.
-   *
-   * @var array
-   */
-  public static $modules = array('file_test');
-
   protected $scheme = 'dummy-readonly';
   protected $classname = 'Drupal\file_test\DummyReadOnlyStreamWrapper';
 
@@ -30,16 +23,6 @@ public static function getInfo() {
     );
   }
 
-  function setUp() {
-    parent::setUp();
-    drupal_static_reset('file_get_stream_wrappers');
-  }
-
-  function tearDown() {
-    parent::tearDown();
-    stream_wrapper_unregister($this->scheme);
-  }
-
   /**
    * Test write functionality of the read-only stream wrapper.
    */
diff --git a/core/modules/system/lib/Drupal/system/Tests/File/RemoteFileDirectoryTest.php b/core/modules/system/lib/Drupal/system/Tests/File/RemoteFileDirectoryTest.php
index 4c7abd2..af39312 100644
--- a/core/modules/system/lib/Drupal/system/Tests/File/RemoteFileDirectoryTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/File/RemoteFileDirectoryTest.php
@@ -19,6 +19,9 @@ class RemoteFileDirectoryTest extends DirectoryTest {
    */
   public static $modules = array('file_test');
 
+  protected $scheme = 'dummy-remote';
+  protected $classname = 'Drupal\file_test\DummyRemoteStreamWrapper';
+
   public static function getInfo() {
     $info = parent::getInfo();
     $info['group'] = 'File API (remote)';
@@ -26,7 +29,7 @@ public static function getInfo() {
   }
 
   function setUp() {
-    parent::setUp('file_test');
+    parent::setUp();
     \Drupal::config('system.file')->set('default_scheme', 'dummy-remote')->save();
   }
 }
diff --git a/core/modules/system/lib/Drupal/system/Tests/File/RemoteFileScanDirectoryTest.php b/core/modules/system/lib/Drupal/system/Tests/File/RemoteFileScanDirectoryTest.php
index fe554cd..93e2016 100644
--- a/core/modules/system/lib/Drupal/system/Tests/File/RemoteFileScanDirectoryTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/File/RemoteFileScanDirectoryTest.php
@@ -19,6 +19,9 @@ class RemoteFileScanDirectoryTest extends ScanDirectoryTest {
    */
   public static $modules = array('file_test');
 
+  protected $scheme = 'dummy-remote';
+  protected $classname = 'Drupal\file_test\DummyRemoteStreamWrapper';
+
   public static function getInfo() {
     $info = parent::getInfo();
     $info['group'] = 'File API (remote)';
@@ -26,7 +29,7 @@ public static function getInfo() {
   }
 
   function setUp() {
-    parent::setUp('file_test');
+    parent::setUp();
     \Drupal::config('system.file')->set('default_scheme', 'dummy-remote')->save();
   }
 }
diff --git a/core/modules/system/lib/Drupal/system/Tests/File/RemoteFileUnmanagedCopyTest.php b/core/modules/system/lib/Drupal/system/Tests/File/RemoteFileUnmanagedCopyTest.php
index 21973ba..d81213e 100644
--- a/core/modules/system/lib/Drupal/system/Tests/File/RemoteFileUnmanagedCopyTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/File/RemoteFileUnmanagedCopyTest.php
@@ -19,6 +19,9 @@ class RemoteFileUnmanagedCopyTest extends UnmanagedCopyTest {
    */
   public static $modules = array('file_test');
 
+  protected $scheme = 'dummy-remote';
+  protected $classname = 'Drupal\file_test\DummyRemoteStreamWrapper';
+
   public static function getInfo() {
     $info = parent::getInfo();
     $info['group'] = 'File API (remote)';
@@ -26,7 +29,7 @@ public static function getInfo() {
   }
 
   function setUp() {
-    parent::setUp('file_test');
+    parent::setUp();
     \Drupal::config('system.file')->set('default_scheme', 'dummy-remote')->save();
   }
 }
diff --git a/core/modules/system/lib/Drupal/system/Tests/File/RemoteFileUnmanagedDeleteRecursiveTest.php b/core/modules/system/lib/Drupal/system/Tests/File/RemoteFileUnmanagedDeleteRecursiveTest.php
index 9fbafac..a43c3a1 100644
--- a/core/modules/system/lib/Drupal/system/Tests/File/RemoteFileUnmanagedDeleteRecursiveTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/File/RemoteFileUnmanagedDeleteRecursiveTest.php
@@ -19,6 +19,9 @@ class RemoteFileUnmanagedDeleteRecursiveTest extends UnmanagedDeleteRecursiveTes
    */
   public static $modules = array('file_test');
 
+  protected $scheme = 'dummy-remote';
+  protected $classname = 'Drupal\file_test\DummyRemoteStreamWrapper';
+
   public static function getInfo() {
     $info = parent::getInfo();
     $info['group'] = 'File API (remote)';
@@ -26,7 +29,7 @@ public static function getInfo() {
   }
 
   function setUp() {
-    parent::setUp('file_test');
+    parent::setUp();
     \Drupal::config('system.file')->set('default_scheme', 'dummy-remote')->save();
   }
 }
diff --git a/core/modules/system/lib/Drupal/system/Tests/File/RemoteFileUnmanagedDeleteTest.php b/core/modules/system/lib/Drupal/system/Tests/File/RemoteFileUnmanagedDeleteTest.php
index b5dfcf7..d6a9b07 100644
--- a/core/modules/system/lib/Drupal/system/Tests/File/RemoteFileUnmanagedDeleteTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/File/RemoteFileUnmanagedDeleteTest.php
@@ -19,6 +19,9 @@ class RemoteFileUnmanagedDeleteTest extends UnmanagedDeleteTest {
    */
   public static $modules = array('file_test');
 
+  protected $scheme = 'dummy-remote';
+  protected $classname = 'Drupal\file_test\DummyRemoteStreamWrapper';
+
   public static function getInfo() {
     $info = parent::getInfo();
     $info['group'] = 'File API (remote)';
@@ -26,7 +29,7 @@ public static function getInfo() {
   }
 
   function setUp() {
-    parent::setUp('file_test');
+    parent::setUp();
     \Drupal::config('system.file')->set('default_scheme', 'dummy-remote')->save();
   }
 }
diff --git a/core/modules/system/lib/Drupal/system/Tests/File/RemoteFileUnmanagedMoveTest.php b/core/modules/system/lib/Drupal/system/Tests/File/RemoteFileUnmanagedMoveTest.php
index 243c22d..52a74fb 100644
--- a/core/modules/system/lib/Drupal/system/Tests/File/RemoteFileUnmanagedMoveTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/File/RemoteFileUnmanagedMoveTest.php
@@ -19,6 +19,9 @@ class RemoteFileUnmanagedMoveTest extends UnmanagedMoveTest {
    */
   public static $modules = array('file_test');
 
+  protected $scheme = 'dummy-remote';
+  protected $classname = 'Drupal\file_test\DummyRemoteStreamWrapper';
+
   public static function getInfo() {
     $info = parent::getInfo();
     $info['group'] = 'File API (remote)';
diff --git a/core/modules/system/lib/Drupal/system/Tests/File/RemoteFileUnmanagedSaveDataTest.php b/core/modules/system/lib/Drupal/system/Tests/File/RemoteFileUnmanagedSaveDataTest.php
index 1e5712a..8dfd0e9 100644
--- a/core/modules/system/lib/Drupal/system/Tests/File/RemoteFileUnmanagedSaveDataTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/File/RemoteFileUnmanagedSaveDataTest.php
@@ -19,6 +19,9 @@ class RemoteFileUnmanagedSaveDataTest extends UnmanagedSaveDataTest {
    */
   public static $modules = array('file_test');
 
+  protected $scheme = 'dummy-remote';
+  protected $classname = 'Drupal\file_test\DummyRemoteStreamWrapper';
+
   public static function getInfo() {
     $info = parent::getInfo();
     $info['group'] = 'File API (remote)';
@@ -26,7 +29,7 @@ public static function getInfo() {
   }
 
   function setUp() {
-    parent::setUp('file_test');
+    parent::setUp();
     \Drupal::config('system.file')->set('default_scheme', 'dummy-remote')->save();
   }
 }
diff --git a/core/modules/system/lib/Drupal/system/Tests/File/StreamWrapperTest.php b/core/modules/system/lib/Drupal/system/Tests/File/StreamWrapperTest.php
index 16bc592..e095ed4 100644
--- a/core/modules/system/lib/Drupal/system/Tests/File/StreamWrapperTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/File/StreamWrapperTest.php
@@ -8,12 +8,11 @@
 namespace Drupal\system\Tests\File;
 
 use Drupal\Core\StreamWrapper\PublicStream;
-use Drupal\simpletest\WebTestBase;
 
 /**
  * Tests stream wrapper functions.
  */
-class StreamWrapperTest extends WebTestBase {
+class StreamWrapperTest extends FileTestBase {
 
   /**
    * Modules to enable.
@@ -33,16 +32,6 @@ public static function getInfo() {
     );
   }
 
-  function setUp() {
-    parent::setUp();
-    drupal_static_reset('file_get_stream_wrappers');
-  }
-
-  function tearDown() {
-    parent::tearDown();
-    stream_wrapper_unregister($this->scheme);
-  }
-
   /**
    * Test the getClassName() function.
    */
diff --git a/core/modules/system/lib/Drupal/system/Tests/File/UrlRewritingTest.php b/core/modules/system/lib/Drupal/system/Tests/File/UrlRewritingTest.php
index 9022632..11f9d16 100644
--- a/core/modules/system/lib/Drupal/system/Tests/File/UrlRewritingTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/File/UrlRewritingTest.php
@@ -7,6 +7,8 @@
 
 namespace Drupal\system\Tests\File;
 
+use Symfony\Component\HttpFoundation\Request;
+
 /**
  * Tests for file URL rewriting.
  */
@@ -23,7 +25,7 @@ public static function getInfo() {
     return array(
       'name' => 'File URL rewriting',
       'description' => 'Tests for file URL rewriting.',
-      'group' => 'File',
+      'group' => 'File API',
     );
   }
 
@@ -95,6 +97,11 @@ function testRelativeFileURL() {
     // Disable file_test.module's hook_file_url_alter() implementation.
     \Drupal::state()->set('file_test.hook_file_url_alter', NULL);
 
+    // Create a mock Request for file_url_transform_relative().
+    $request = Request::create($GLOBALS['base_url']);
+    $this->container->set('request', $request);
+    \Drupal::setContainer($this->container);
+
     // Shipped file.
     $filepath = 'core/assets/vendor/jquery/jquery.js';
     $url = file_create_url($filepath);