diff -u b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
--- b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
@@ -752,13 +752,18 @@
     install_drupal($parameters);
 
     // Set the install_profile so that web requests to the requests to the child
-    // site have the correct profile.
+    // site have the correct profile. Set the file_private_path so that
+    // system_stream_wrappers() returns the correct stream wrappers.
     $settings = array(
       'settings' => array(
         'install_profile' => (object) array(
           'value' => $this->profile,
           'required' => TRUE,
         ),
+        'file_private_path' => (object) array(
+            'value' => $this->private_files_directory,
+            'required' => TRUE,
+        ),
       ),
     );
     $this->writeSettings($settings);
diff -u b/core/modules/system/system.module b/core/modules/system/system.module
--- b/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -1914,7 +1914,7 @@
   );
 
   // Only register the private file stream wrapper if a file path has been set.
-  if (settings()->get('file_private_path')) {
+  if (\Drupal::config('system.file')->get('path.private')) {
     $wrappers['private'] = array(
       'name' => t('Private files'),
       'class' => 'Drupal\Core\StreamWrapper\PrivateStream',
@@ -2116,7 +2116,7 @@
   );
 
   // Only register the private file stream wrapper if a file path has been set.
-  if (\Drupal::config('system.file')->get('path.private')) {
+  if (settings()->get('file_private_path')) {
     $wrappers['private'] = array(
       'name' => t('Private files'),
       'class' => 'Drupal\Core\StreamWrapper\PrivateStream',
only in patch2:
unchanged:
--- a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/Dump/Drupal6SystemFile.php
+++ b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/Dump/Drupal6SystemFile.php
@@ -27,10 +27,6 @@ public static function load(Connection $database) {
       'value',
     ))
     ->values(array(
-      'name' => 'file_directory_path',
-      'value' => 's:10:"files/test";',
-    ))
-    ->values(array(
       'name' => 'file_directory_temp',
       'value' => 's:10:"files/temp";',
     ))
only in patch2:
unchanged:
--- a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateSystemConfigsTest.php
+++ b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateSystemConfigsTest.php
@@ -184,7 +184,6 @@ public function testSystemFile() {
     $old_state = \Drupal::configFactory()->getOverrideState();
     \Drupal::configFactory()->setOverrideState(FALSE);
     $config = \Drupal::config('system.file');
-    $this->assertIdentical($config->get('path.private'), 'files/test');
     $this->assertIdentical($config->get('path.temporary'), 'files/temp');
     \Drupal::configFactory()->setOverrideState($old_state);
   }
only in patch2:
unchanged:
--- a/core/modules/system/lib/Drupal/system/Tests/Installer/InstallerTranslationTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Installer/InstallerTranslationTest.php
@@ -35,7 +35,6 @@ protected function setUp() {
 
     $variable_groups = array(
       'system.file' => array(
-        'path.private' =>  $this->private_files_directory,
         'path.temporary' => $this->temp_files_directory,
       ),
       'locale.settings' => array(
only in patch2:
unchanged:
--- a/core/modules/system/lib/Drupal/system/Tests/InstallerTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/InstallerTest.php
@@ -35,7 +35,6 @@ protected function setUp() {
 
     $variable_groups = array(
       'system.file' => array(
-        'path.private' =>  $this->private_files_directory,
         'path.temporary' =>  $this->temp_files_directory,
       ),
       'locale.settings' =>  array(