diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index 697f17f..471d5c4 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -519,10 +519,8 @@ function drupal_valid_http_host($host) {
  * Sets the base URL, cookie domain, and session name from configuration.
  */
 function drupal_settings_initialize() {
-  global $base_url, $base_path, $base_root, $script_path;
-
   // Export these settings.php variables to the global namespace.
-  global $databases, $cookie_domain, $conf, $db_prefix, $drupal_hash_salt, $base_secure_url, $base_insecure_url, $config_directories;
+  global $base_url, $databases, $cookie_domain, $conf, $drupal_hash_salt, $config_directories;
   $conf = array();
 
   // Make conf_path() available as local variable in settings.php.
@@ -532,6 +530,20 @@ function drupal_settings_initialize() {
   }
 
   new Settings(isset($settings) ? $settings : array());
+}
+
+/**
+ * Initializes global request variables.
+ *
+ * @todo D8: Eliminate this entirely in favor of Request object.
+ */
+function drupal_request_initialize() {
+  // Provided by settings.php.
+  // @see drupal_settings_initialize()
+  global $base_url, $cookie_domain;
+  // Set and derived from $base_url by this function.
+  global $base_path, $base_root, $script_path;
+  global $base_secure_url, $base_insecure_url;
 
   $is_https = isset($_SERVER['HTTPS']) && strtolower($_SERVER['HTTPS']) == 'on';
 
@@ -1910,6 +1922,7 @@ function _drupal_bootstrap_configuration() {
   drupal_environment_initialize();
   // Initialize the configuration, including variables from settings.php.
   drupal_settings_initialize();
+  drupal_request_initialize();
 
   // Make sure we are using the test database prefix in child Drupal sites.
   if ($test_prefix = drupal_valid_test_ua()) {
@@ -1920,6 +1933,10 @@ function _drupal_bootstrap_configuration() {
     $test_info = &$GLOBALS['drupal_test_info'];
     $test_info['test_run_id'] = $test_prefix;
     $test_info['in_child_site'] = TRUE;
+
+    // Log fatal errors to the test site directory.
+    ini_set('log_errors', 1);
+    ini_set('error_log', DRUPAL_ROOT . '/sites/simpletest/' . substr($test_prefix, 10) . '/error.log');
   }
 
   // Activate the class loader.
@@ -2167,7 +2184,16 @@ function drupal_valid_test_ua($new_prefix = NULL) {
     list(, $prefix, $time, $salt, $hmac) = $matches;
     $check_string =  $prefix . ';' . $time . ';' . $salt;
     // Read the hash salt prepared by drupal_generate_test_ua().
-    require DRUPAL_ROOT . '/sites/simpletest/' . substr($prefix, 10) . '/key.php';
+    // This function is called before settings.php is read and Drupal's error
+    // handlers are set up. While Drupal's error handling may be properly
+    // configured on production sites, the server's PHP error_reporting may not.
+    // Ensure that no information leaks on production sites.
+    $key_file = DRUPAL_ROOT . '/sites/simpletest/' . substr($prefix, 10) . '/key.php';
+    if (!is_readable($key_file)) {
+      header($_SERVER['SERVER_PROTOCOL'] . ' 403 Forbidden');
+      exit;
+    }
+    require $key_file;
     // The file properties add more entropy not easily accessible to others.
     $key = $private_key . filectime(__FILE__) . fileinode(__FILE__);
     $time_diff = REQUEST_TIME - $time;
diff --git a/core/includes/common.inc b/core/includes/common.inc
index 0099008..cb4e161 100644
--- a/core/includes/common.inc
+++ b/core/includes/common.inc
@@ -3060,14 +3060,6 @@ function _drupal_bootstrap_code() {
   // Make sure all stream wrappers are registered.
   file_get_stream_wrappers();
 
-  // Now that stream wrappers are registered, log fatal errors from a simpletest
-  // child site to a test specific file directory.
-  $test_info = &$GLOBALS['drupal_test_info'];
-  if (!empty($test_info['in_child_site'])) {
-    ini_set('log_errors', 1);
-    ini_set('error_log', 'public://error.log');
-  }
-
   // Set the allowed protocols once we have the config available.
   $allowed_protocols = \Drupal::config('system.filter')->get('protocols');
   if (!isset($allowed_protocols)) {
diff --git a/core/includes/file.inc b/core/includes/file.inc
index 545fca3..622a6ca 100644
--- a/core/includes/file.inc
+++ b/core/includes/file.inc
@@ -575,12 +575,12 @@ function file_ensure_htaccess() {
  */
 function file_save_htaccess($directory, $private = TRUE) {
   if (file_uri_scheme($directory)) {
-    $directory = file_stream_wrapper_uri_normalize($directory);
+    $htaccess_path = file_stream_wrapper_uri_normalize($directory . '/.htaccess');
   }
   else {
     $directory = rtrim($directory, '/\\');
+    $htaccess_path = $directory . '/.htaccess';
   }
-  $htaccess_path =  $directory . '/.htaccess';
 
   if (file_exists($htaccess_path)) {
     // Short circuit if the .htaccess file already exists.
diff --git a/core/includes/install.core.inc b/core/includes/install.core.inc
index 2ef6b95..4897ef2 100644
--- a/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -1148,13 +1148,13 @@ function install_settings_form($form, &$form_state, &$install_state) {
  */
 function install_settings_form_validate($form, &$form_state) {
   $driver = $form_state['values']['driver'];
-  $database = $form_state['values'][$driver];
-  // When testing the interactive installer, copy the database password and
-  // the test prefix.
-  // @todo Remove this; pass prefix in POST data instead.
-  if ($test_prefix = drupal_valid_test_ua()) {
-    $database['prefix'] = $test_prefix;
+
+  // @todo Remove when PIFR submits 'prefix' instead of 'db_prefix'.
+  if (!empty($form_state['input'][$driver]['db_prefix'])) {
+    $form_state['values'][$driver]['prefix'] = $form_state['input'][$driver]['db_prefix'];
   }
+  $database = $form_state['values'][$driver];
+
   $drivers = drupal_get_database_types();
   $reflection = new \ReflectionClass($drivers[$driver]);
   $install_namespace = $reflection->getNamespaceName();
@@ -1162,13 +1162,6 @@ function install_settings_form_validate($form, &$form_state) {
   $database['namespace'] = substr($install_namespace, 0, strrpos($install_namespace, '\\'));
   $database['driver'] = $driver;
 
-  // @todo PIFR uses 'db_prefix' instead of 'prefix'. Remove this when it gets
-  //   fixed.
-  if (!$test_prefix && isset($database['db_prefix'])) {
-    $database['prefix'] = $database['db_prefix'];
-  }
-  unset($database['db_prefix']);
-
   $form_state['storage']['database'] = $database;
   $errors = install_database_errors($database, $form_state['values']['settings_file']);
   foreach ($errors as $name => $message) {
diff --git a/core/lib/Drupal/Core/Database/Install/Tasks.php b/core/lib/Drupal/Core/Database/Install/Tasks.php
index e80dd86..f950647 100644
--- a/core/lib/Drupal/Core/Database/Install/Tasks.php
+++ b/core/lib/Drupal/Core/Database/Install/Tasks.php
@@ -251,14 +251,14 @@ public function getFormOptions(array $database) {
       '#weight' => 10,
     );
 
-    $profile = drupal_get_profile();
-    $db_prefix = ($profile == 'standard') ? 'drupal_' : $profile . '_';
-    $form['advanced_options']['db_prefix'] = array(
+    $form['advanced_options']['prefix'] = array(
       '#type' => 'textfield',
       '#title' => t('Table name prefix'),
       '#default_value' => '',
       '#size' => 45,
-      '#description' => t('If more than one application will be sharing this database, a unique table name prefix–such as %prefix–will prevent collisions.', array('%prefix' => $db_prefix)),
+      '#description' => t('If more than one application will be sharing this database, a unique table name prefix–such as %prefix–will prevent collisions.', array(
+        '%prefix' => preg_replace('@[^a-z0-9]@', '_', strtolower(drupal_install_profile_distribution_name())) . '_',
+      )),
       '#weight' => 10,
     );
 
diff --git a/core/lib/Drupal/Core/DrupalKernel.php b/core/lib/Drupal/Core/DrupalKernel.php
index f6a1810..e7a18b9 100644
--- a/core/lib/Drupal/Core/DrupalKernel.php
+++ b/core/lib/Drupal/Core/DrupalKernel.php
@@ -334,17 +334,13 @@ public function updateModules(array $module_list, array $module_filenames = arra
   }
 
   /**
-   * Returns the classname based on environment and testing prefix.
+   * Returns the classname based on environment.
    *
    * @return string
    *   The class name.
    */
   protected function getClassName() {
     $parts = array('service_container', $this->environment);
-    // Make sure to use a testing-specific container even in the parent site.
-    if ($prefix = drupal_valid_test_ua()) {
-      $parts[] = $prefix;
-    }
     return implode('_', $parts);
   }
 
diff --git a/core/modules/file/tests/file_test/lib/Drupal/file_test/DummyReadOnlyStreamWrapper.php b/core/modules/file/tests/file_test/lib/Drupal/file_test/DummyReadOnlyStreamWrapper.php
index b427d3f..d230bc5 100644
--- a/core/modules/file/tests/file_test/lib/Drupal/file_test/DummyReadOnlyStreamWrapper.php
+++ b/core/modules/file/tests/file_test/lib/Drupal/file_test/DummyReadOnlyStreamWrapper.php
@@ -16,7 +16,7 @@
  */
 class DummyReadOnlyStreamWrapper extends LocalReadOnlyStream {
   function getDirectoryPath() {
-    return 'sites/default/files';
+    return conf_path() . '/files';
   }
 
   /**
diff --git a/core/modules/file/tests/file_test/lib/Drupal/file_test/DummyStreamWrapper.php b/core/modules/file/tests/file_test/lib/Drupal/file_test/DummyStreamWrapper.php
index 4836f09..cbea40f 100644
--- a/core/modules/file/tests/file_test/lib/Drupal/file_test/DummyStreamWrapper.php
+++ b/core/modules/file/tests/file_test/lib/Drupal/file_test/DummyStreamWrapper.php
@@ -16,7 +16,7 @@
  */
 class DummyStreamWrapper extends LocalStream {
   function getDirectoryPath() {
-    return 'sites/default/files';
+    return conf_path() . '/files';
   }
 
   /**
diff --git a/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
index 2209555..0be7bd9 100644
--- a/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
@@ -872,20 +872,10 @@ protected function changeDatabasePrefix() {
     $connection_info = Database::getConnectionInfo('default');
     Database::renameConnection('default', 'simpletest_original_default');
     foreach ($connection_info as $target => $value) {
-      $connection_info[$target]['prefix'] = array(
-        'default' => $value['prefix']['default'] . $this->databasePrefix,
-      );
+      $connection_info[$target]['prefix'] = $value['prefix']['default'] . $this->databasePrefix;
     }
     Database::addConnectionInfo('default', 'default', $connection_info['default']);
 
-    // Additionally override global $databases, since the installer does not use
-    // the Database connection info.
-    // @see install_verify_database_settings()
-    // @see install_database_errors()
-    // @todo Fix installer to use Database connection info.
-    global $databases;
-    $databases['default']['default'] = $connection_info['default'];
-
     // Indicate the database prefix was set up correctly.
     $this->setupDatabasePrefix = TRUE;
   }
@@ -950,29 +940,30 @@ protected function prepareEnvironment() {
 
     // Create test directory ahead of installation so fatal errors and debug
     // information can be logged during installation process.
+    file_prepare_directory($this->siteDirectory, FILE_CREATE_DIRECTORY | FILE_MODIFY_PERMISSIONS);
+
+    // Prepare filesystem directory paths.
     $this->public_files_directory = $this->siteDirectory . '/files';
     $this->private_files_directory = $this->siteDirectory . '/private';
     $this->temp_files_directory = $this->siteDirectory . '/temp';
     $this->translation_files_directory = $this->siteDirectory . '/translations';
 
-    // Create the directories
-    file_prepare_directory($this->siteDirectory, FILE_CREATE_DIRECTORY | FILE_MODIFY_PERMISSIONS);
-    // @todo Do not create these for WebTestBase; rely on installer.
-    file_prepare_directory($this->public_files_directory, FILE_CREATE_DIRECTORY | FILE_MODIFY_PERMISSIONS);
-    file_prepare_directory($this->private_files_directory, FILE_CREATE_DIRECTORY);
-    file_prepare_directory($this->temp_files_directory, FILE_CREATE_DIRECTORY);
-    file_prepare_directory($this->translation_files_directory, FILE_CREATE_DIRECTORY);
-    $this->generatedTestFiles = FALSE;
-
-    // Create and set new configuration directories.
-    // @todo Only valid for tests not executing the installer (in any way).
+    // Create filesystem directories, unless the installer will be executed.
+    // @todo Move into DrupalUnitTestBase::setUp().
     if (!$this instanceof WebTestBase) {
+      file_prepare_directory($this->public_files_directory, FILE_CREATE_DIRECTORY | FILE_MODIFY_PERMISSIONS);
+      file_prepare_directory($this->private_files_directory, FILE_CREATE_DIRECTORY);
+      file_prepare_directory($this->temp_files_directory, FILE_CREATE_DIRECTORY);
+      file_prepare_directory($this->translation_files_directory, FILE_CREATE_DIRECTORY);
+
+      // Create and set new configuration directories.
       $this->prepareConfigDirectories();
     }
     else {
       $GLOBALS['config_directories'] = array();
       $this->configDirectories = array();
     }
+    $this->generatedTestFiles = FALSE;
 
     // Reset statics before the old container is replaced so that objects with a
     // __destruct() method still have access to it.
@@ -999,7 +990,7 @@ protected function prepareEnvironment() {
 
     // Log fatal errors.
     ini_set('log_errors', 1);
-    ini_set('error_log', $this->public_files_directory . '/error.log');
+    ini_set('error_log', $this->siteDirectory . '/error.log');
 
     // Set the test information for use in other parts of Drupal.
     $test_info = &$GLOBALS['drupal_test_info'];
@@ -1052,11 +1043,11 @@ protected function prepareConfigDirectories() {
    *   tests can invoke this workaround when requiring services from newly
    *   enabled modules to be immediately available in the same request.
    */
-  protected function rebuildContainer() {
+  protected function rebuildContainer($environment = 'testing') {
     // Preserve the request object after the container rebuild.
     $request = \Drupal::request();
 
-    $this->kernel = new DrupalKernel('testing', drupal_classloader(), FALSE);
+    $this->kernel = new DrupalKernel($environment, drupal_classloader(), FALSE);
     $this->kernel->boot();
     // DrupalKernel replaces the container in \Drupal::getContainer() with a
     // different object, so we need to replace the instance on this test class.
diff --git a/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
index 0d73cfa..3f13782 100644
--- a/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
@@ -9,6 +9,7 @@
 
 use Drupal\Component\Utility\Crypt;
 use Drupal\Component\Utility\NestedArray;
+use Drupal\Component\Utility\Settings;
 use Drupal\Component\Utility\String;
 use Drupal\Core\DrupalKernel;
 use Drupal\Core\Database\Database;
@@ -47,7 +48,21 @@
   protected $curlHandle;
 
   /**
-   * The headers of the page currently loaded in the internal browser.
+   * The request headers of all requests performed.
+   *
+   * @var array
+   */
+  protected $requestHeaders;
+
+  /**
+   * The response headers of all requests performed.
+   *
+   * @var array
+   */
+  protected $responseHeaders;
+
+  /**
+   * The response headers of the page currently loaded in the internal browser.
    *
    * @var Array
    */
@@ -731,10 +746,6 @@ protected function setUp() {
     // Reset all variables to perform tests in a clean environment.
     $conf = array();
 
-    // Add the parent profile's search path to the child site's search paths.
-    // @see drupal_system_listing()
-    $conf['simpletest.settings']['parent_profile'] = $this->originalProfile;
-
     // Define information about the user 1 account.
     $this->root_user = new UserSession(array(
       'uid' => 1,
@@ -747,22 +758,84 @@ protected function setUp() {
     $batch = &batch_get();
     $batch = array();
 
-    $this->settingsSet('file_public_path', $this->public_files_directory);
+    // Get parameters for install_drupal() before removing global variables.
+    $parameters = $this->installParameters();
+
+    // Prepare installer settings that are not install_drupal() parameters.
+    // Copy and prepare an actual settings.php, so as to resemble a regular
+    // installation.
+    copy(DRUPAL_ROOT . '/sites/default/default.settings.php', DRUPAL_ROOT . '/' . $this->siteDirectory . '/settings.php');
+
+    // All file system paths are set up by System module during installation.
+    // @see system_requirements()
+    // @see TestBase::prepareEnvironment()
+    $settings['settings']['file_public_path'] = (object) array(
+      'value' => $this->public_files_directory,
+      'required' => TRUE,
+    );
+    // @todo While private/temporary filesystem paths can be preset in the
+    //   installer via global configuration overrides, some tests expect the
+    //   values to be configurable through the UI. By setting them in
+    //   settings.php, they are no longer configurable... Why are these not
+    //   settings like the public filesystem path to begin with? (consistency)
+    /*
+    $settings['conf']['system.file']['path']['private'] = (object) array(
+      'value' => $this->private_files_directory,
+      'required' => TRUE,
+    );
+    $settings['conf']['system.file']['path']['temporary'] = (object) array(
+      'value' => $this->temp_files_directory,
+      'required' => TRUE,
+    );
+    */
+    // Use the test mail class instead of the default mail handler class.
+    $settings['conf']['system.mail']['interface']['default'] = (object) array(
+      'value' => 'Drupal\Core\Mail\TestMailCollector',
+      'required' => TRUE,
+    );
+    // Add the parent profile's search path to the child site's search paths.
+    // @see drupal_system_listing()
+    $settings['conf']['simpletest.settings']['parent_profile'] = (object) array(
+      'value' => $this->originalProfile,
+      'required' => TRUE,
+    );
+    $this->writeSettings($settings);
+
+    // Since Drupal is bootstrapped already, install_begin_request() will not
+    // bootstrap into DRUPAL_BOOTSTRAP_CONFIGURATION (again). Hence, we have to
+    // reload the new settings.php manually.
+    drupal_settings_initialize();
+
     // Execute the non-interactive installer.
     require_once DRUPAL_ROOT . '/core/includes/install.core.inc';
-    $parameters = $this->installParameters();
     install_drupal($parameters);
 
+    // Import new settings.php.
+    global $databases, $config_directories, $settings, $conf;
+    $settings = array();
+    include DRUPAL_ROOT . '/' . $this->siteDirectory . '/settings.php';
+    foreach ($config_directories as $type => $path) {
+      $this->configDirectories[$type] = $this->siteDirectory . '/' . $path;
+    }
+    // Consume new settings written by the installer.
+    new Settings($settings);
+
     // After writing settings.php, the installer removes write permissions
     // from the site directory. To allow drupal_generate_test_ua() to write
     // a key.php file containing the private key for drupal_valid_test_ua(),
     // the site directory has to be writable.
     // Use chmod() without a Drupal wrapper, so potential errors are visible.
+    // WebTestBase::tearDown() will delete the entire test site directory.
     chmod(DRUPAL_ROOT . '/' . $this->siteDirectory, 0777);
 
-    // Override install profile in Settings to so the correct profile is used by
-    // tests.
-    $this->settingsSet('install_profile', $this->profile);
+    // Manually provide private and temporary files directories.
+    // (see @todo above)
+    file_prepare_directory($this->private_files_directory, FILE_CREATE_DIRECTORY);
+    file_prepare_directory($this->temp_files_directory, FILE_CREATE_DIRECTORY);
+    \Drupal::config('system.file')
+      ->set('path.private', $this->private_files_directory)
+      ->set('path.temporary', $this->temp_files_directory)
+      ->save();
 
     $this->rebuildContainer();
 
@@ -770,13 +843,6 @@ protected function setUp() {
     $batch = &batch_get();
     $batch = $this->originalBatch;
 
-    // Set path variables.
-
-    // Set 'parent_profile' of simpletest to add the parent profile's
-    // search path to the child site's search paths.
-    // @see drupal_system_listing()
-    \Drupal::config('simpletest.settings')->set('parent_profile', $this->originalProfile)->save();
-
     // Collect modules to install.
     $class = get_class($this);
     $modules = array();
@@ -791,13 +857,11 @@ protected function setUp() {
       $success = \Drupal::moduleHandler()->install($modules, TRUE);
       $this->assertTrue($success, t('Enabled modules: %modules', array('%modules' => implode(', ', $modules))));
       $this->rebuildContainer();
-    }
 
-    // Reset/rebuild all data structures after enabling the modules.
-    $this->resetAll();
-
-    // Use the test mail class instead of the default mail handler class.
-    \Drupal::config('system.mail')->set('interface.default', 'Drupal\Core\Mail\TestMailCollector')->save();
+      // Reset static variables after enabling additional test modules.
+      // Affects e.g. file_get_stream_wrappers().
+      drupal_static_reset();
+    }
 
     drupal_set_time_limit($this->timeLimit);
     // Temporary fix so that when running from run-tests.sh we don't get an
@@ -817,6 +881,10 @@ protected function setUp() {
    */
   protected function installParameters() {
     $connection_info = Database::getConnectionInfo();
+    $driver = $connection_info['default']['driver'];
+    unset($connection_info['default']['driver']);
+    unset($connection_info['default']['pdo']);
+    unset($connection_info['default']['init_commands']);
     $parameters = array(
       'interactive' => FALSE,
       'parameters' => array(
@@ -824,7 +892,10 @@ protected function installParameters() {
         'langcode' => 'en',
       ),
       'forms' => array(
-        'install_settings_form' => $connection_info['default'],
+        'install_settings_form' => array(
+          'driver' => $driver,
+          $driver => $connection_info['default'],
+        ),
         'install_configure_form' => array(
           'site_name' => 'Drupal',
           'site_mail' => 'simpletest@example.com',
@@ -868,8 +939,7 @@ protected function writeSettings($settings) {
     }
 
     include_once DRUPAL_ROOT . '/core/includes/install.inc';
-    $filename = $this->public_files_directory . '/settings.php';
-    file_put_contents($filename, "<?php\n");
+    $filename = $this->siteDirectory . '/settings.php';
     drupal_rewrite_settings($settings, $filename);
 
     // Restore the original globals.
@@ -919,8 +989,8 @@ protected function writeCustomTranslations() {
   /**
    * Overrides \Drupal\simpletest\TestBase::rebuildContainer().
    */
-  protected function rebuildContainer() {
-    parent::rebuildContainer();
+  protected function rebuildContainer($environment = 'prod') {
+    parent::rebuildContainer($environment);
     // Make sure the url generator has a request object, otherwise calls to
     // $this->drupalGet() will fail.
     $this->prepareRequestForGenerator();
@@ -1021,6 +1091,7 @@ protected function curlInitialize() {
         CURLOPT_SSL_VERIFYHOST => FALSE,
         CURLOPT_HEADERFUNCTION => array(&$this, 'curlHeaderCallback'),
         CURLOPT_USERAGENT => $this->databasePrefix,
+        CURLINFO_HEADER_OUT => TRUE,
       );
       if (isset($this->httpauth_credentials)) {
         $curl_options[CURLOPT_HTTPAUTH] = $this->httpauth_method;
@@ -1132,13 +1203,25 @@ protected function curlExec($curl_options, $redirect = FALSE) {
     if (!$redirect) {
       // Reset headers, the session ID and the redirect counter.
       $this->session_id = NULL;
-      $this->headers = array();
+      $this->requestId = 0;
+      $this->requestHeaders = array();
+      $this->responseHeaders = array();
       $this->redirect_count = 0;
     }
 
+    $this->headers = array();
     $content = curl_exec($this->curlHandle);
     $status = curl_getinfo($this->curlHandle, CURLINFO_HTTP_CODE);
 
+    $this->requestHeaders[$this->requestId] = curl_getinfo($this->curlHandle, CURLINFO_HEADER_OUT);
+
+    $response_headers = $this->headers;
+    $this->responseHeaders[$this->requestId] = array_shift($response_headers);
+    sort($response_headers);
+    $this->responseHeaders[$this->requestId] .= implode('', $response_headers);
+
+    $this->requestId++;
+
     // cURL incorrectly handles URLs with fragments, so instead of
     // letting cURL handle redirects we take of them ourselves to
     // to prevent fragments being sent to the web server as part
@@ -1286,7 +1369,10 @@ protected function drupalGet($path, array $options = array(), array $headers = a
     $verbose = 'GET request to: ' . $path .
                '<hr />Ending URL: ' . $this->getUrl();
     if ($this->dumpHeaders) {
-      $verbose .= '<hr />Headers: <pre>' . check_plain(var_export(array_map('trim', $this->headers), TRUE)) . '</pre>';
+      for ($i = 0; $i < $this->requestId; $i++) {
+        $verbose .= '<hr />Request headers: <pre>' . check_plain($this->requestHeaders[$i]) . '</pre>';
+        $verbose .= '<hr />Response headers: <pre>' . check_plain($this->responseHeaders[$i]) . '</pre>';
+      }
     }
     $verbose .= '<hr />' . $out;
 
@@ -1476,7 +1562,10 @@ protected function drupalPostForm($path, $edit, $submit, array $options = array(
           $verbose = 'POST request to: ' . $path;
           $verbose .= '<hr />Ending URL: ' . $this->getUrl();
           if ($this->dumpHeaders) {
-            $verbose .= '<hr />Headers: <pre>' . check_plain(var_export(array_map('trim', $this->headers), TRUE)) . '</pre>';
+            for ($i = 0; $i < $this->requestId; $i++) {
+              $verbose .= '<hr />Request headers: <pre>' . check_plain($this->requestHeaders[$i]) . '</pre>';
+              $verbose .= '<hr />Response headers: <pre>' . check_plain($this->responseHeaders[$i]) . '</pre>';
+            }
           }
           $verbose .= '<hr />Fields: ' . highlight_string('<?php ' . var_export($post_array, TRUE), TRUE);
           $verbose .= '<hr />' . $out;
@@ -1840,14 +1929,16 @@ protected function drupalHead($path, array $options = array(), array $headers =
     $options['absolute'] = TRUE;
     $url = $this->container->get('url_generator')->generateFromPath($path, $options);
     $out = $this->curlExec(array(CURLOPT_NOBODY => TRUE, CURLOPT_URL => $url, CURLOPT_HTTPHEADER => $headers));
-    // Ensure that any changes to variables in the other thread are picked up.
-    $this->refreshVariables();
 
+    $verbose = 'HEAD request to: ' . $path;
+    $verbose .= '<hr />Ending URL: ' . $this->getUrl();
     if ($this->dumpHeaders) {
-      $this->verbose('GET request to: ' . $path .
-                     '<hr />Ending URL: ' . $this->getUrl() .
-                     '<hr />Headers: <pre>' . check_plain(var_export(array_map('trim', $this->headers), TRUE)) . '</pre>');
+      for ($i = 0; $i < $this->requestId; $i++) {
+        $verbose .= '<hr />Request headers: <pre>' . check_plain($this->requestHeaders[$i]) . '</pre>';
+        $verbose .= '<hr />Response headers: <pre>' . check_plain($this->responseHeaders[$i]) . '</pre>';
+      }
     }
+    $this->verbose($verbose);
 
     return $out;
   }
diff --git a/core/modules/simpletest/simpletest.install b/core/modules/simpletest/simpletest.install
index 4b940ed..a4a17b7 100644
--- a/core/modules/simpletest/simpletest.install
+++ b/core/modules/simpletest/simpletest.install
@@ -58,6 +58,20 @@ function simpletest_requirements($phase) {
     $requirements['php_memory_limit']['description'] = t('The testing framework requires the PHP memory limit to be at least %memory_minimum_limit. The current value is %memory_limit. <a href="@url">Follow these steps to continue</a>.', array('%memory_limit' => $memory_limit, '%memory_minimum_limit' => SIMPLETEST_MINIMUM_PHP_MEMORY_LIMIT, '@url' => 'http://drupal.org/node/207036'));
   }
 
+  if ($phase == 'runtime') {
+    $site_directory = 'sites/simpletest';
+    if (!drupal_verify_install_file(DRUPAL_ROOT . '/' . $site_directory, FILE_EXIST|FILE_WRITABLE, 'dir') {
+      $requirements['simpletest_site_directory'] = array(
+        'title' => t('Simpletest site directory'),
+        'value' => is_dir(DRUPAL_ROOT . '/' . $site_directory) ? t('Not writable') : t('Missing'),
+        'severity' => REQUIREMENT_ERROR,
+        'description' => t('The testing framework requires the !test-sites-directory to exist and be writable in order to run tests.', array(
+          '!test-sites-directory' => '<code>./' . $site_directory . '</code>',
+        )),
+      );
+    }
+  }
+
   return $requirements;
 }
 
@@ -154,6 +168,20 @@ function simpletest_schema() {
 }
 
 /**
+ * Implements hook_install().
+ */
+function simpletest_install() {
+  // Attempt to automatically create the sites directory for tests.
+  // @see simpletest_requirements()
+  $site_directory = 'sites/simpletest';
+  if (!drupal_install_mkdir(DRUPAL_ROOT . '/' . $site_directory, FILE_READABLE|FILE_WRITABLE|FILE_EXECUTABLE)) {
+    drupal_set_message(t('The test sites directory !directory could not be created automatically. Create it manually and make it writable for the web server.', array(
+      '!directory' => '<code>./' . $site_directory . '</code>',
+    )), 'warning');
+  }
+}
+
+/**
  * Implements hook_uninstall().
  */
 function simpletest_uninstall() {
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..70fa934 100644
--- a/core/modules/system/lib/Drupal/system/Tests/File/FileTestBase.php
+++ b/core/modules/system/lib/Drupal/system/Tests/File/FileTestBase.php
@@ -16,16 +16,6 @@
  */
 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();
-  }
-
   /**
    * Check that two files have the same values for all fields other than the
    * timestamp.
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..5f3ea59 100644
--- a/core/modules/system/lib/Drupal/system/Tests/File/ReadOnlyStreamWrapperTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/File/ReadOnlyStreamWrapperTest.php
@@ -30,14 +30,9 @@ public static function getInfo() {
     );
   }
 
-  function setUp() {
-    parent::setUp();
-    drupal_static_reset('file_get_stream_wrappers');
-  }
-
   function tearDown() {
-    parent::tearDown();
     stream_wrapper_unregister($this->scheme);
+    parent::tearDown();
   }
 
   /**
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..6ce6568 100644
--- a/core/modules/system/lib/Drupal/system/Tests/File/StreamWrapperTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/File/StreamWrapperTest.php
@@ -33,14 +33,9 @@ public static function getInfo() {
     );
   }
 
-  function setUp() {
-    parent::setUp();
-    drupal_static_reset('file_get_stream_wrappers');
-  }
-
   function tearDown() {
-    parent::tearDown();
     stream_wrapper_unregister($this->scheme);
+    parent::tearDown();
   }
 
   /**
diff --git a/core/modules/system/system.install b/core/modules/system/system.install
index 2598cea..ab6fd81 100644
--- a/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -330,11 +330,11 @@ function system_requirements($phase) {
       // in the intended site directory, so don't require it.
       $directories[] = conf_path(FALSE) . '/files';
     }
-    if (!empty($conf['system.file']['path.private'])) {
-      $directories[] = $conf['system.file']['path.private'];
+    if (!empty($conf['system.file']['path']['private'])) {
+      $directories[] = $conf['system.file']['path']['private'];
     }
-    if (!empty($conf['system.file']['path.temporary'])) {
-      $directories[] = $conf['system.file']['path.temporary'];
+    if (!empty($conf['system.file']['path']['temporary'])) {
+      $directories[] = $conf['system.file']['path']['temporary'];
     }
     else {
       // If the temporary directory is not overridden use an appropriate
diff --git a/core/scripts/run-tests.sh b/core/scripts/run-tests.sh
index e9f0ffe..6af207a 100755
--- a/core/scripts/run-tests.sh
+++ b/core/scripts/run-tests.sh
@@ -585,10 +585,9 @@ function simpletest_script_cleanup($test_id, $test_class, $exitcode) {
   // Read the log file in case any fatal errors caused the test to crash.
   simpletest_log_read($test_id, $db_prefix, $test_class);
 
-  // Check whether a test file directory was setup already.
-  // @see prepareEnvironment()
-  $public_files = PublicStream::basePath();
-  $test_directory = $public_files . '/simpletest/' . substr($db_prefix, 10);
+  // Check whether a test site directory was setup already.
+  // @see \Drupal\simpletest\TestBase::prepareEnvironment()
+  $test_directory = DRUPAL_ROOT . '/sites/simpletest/' . substr($db_prefix, 10);
   if (is_dir($test_directory)) {
     // Output the error_log.
     if (is_file($test_directory . '/error.log')) {
@@ -597,8 +596,7 @@ function simpletest_script_cleanup($test_id, $test_class, $exitcode) {
         $messages[] = $errors;
       }
     }
-
-    // Delete the test files directory.
+    // Delete the test site directory.
     // simpletest_clean_temporary_directories() cannot be used here, since it
     // would also delete file directories of other tests that are potentially
     // running concurrently.