diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index e6339cc..3f38249 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -2478,7 +2478,8 @@ function drupal_container(Container $new_container = NULL, $rebuild = FALSE) {
 
     // Register the KeyValueStore factory.
     $container
-      ->register('keyvalue', 'Drupal\Core\KeyValueStore\KeyValueFactory');
+      ->register('keyvalue', 'Drupal\Core\KeyValueStore\KeyValueFactory')
+      ->addArgument('Drupal\Core\KeyValueStore\DatabaseStorage');
   }
   return $container;
 }
diff --git a/core/includes/module.inc b/core/includes/module.inc
index 5a17873..bc5112d 100644
--- a/core/includes/module.inc
+++ b/core/includes/module.inc
@@ -182,7 +182,7 @@ function system_list($type) {
       // Drupal installations, which might have modules installed in different
       // locations in the file system. The ordering here must also be
       // consistent with the one used in module_implements().
-      $enabled_modules = config('system.module')->get('enabled');
+      $enabled_modules = (array) config('system.module')->get('enabled');
       $module_files = state()->get('system.module.files');
       foreach ($enabled_modules as $name => $weight) {
         // Build a list of all enabled modules.
@@ -196,7 +196,7 @@ function system_list($type) {
       }
 
       // Build a list of themes.
-      $enabled_themes = config('system.theme')->get('enabled');
+      $enabled_themes = (array) config('system.theme')->get('enabled');
       // @todo Themes include all themes, including disabled/uninstalled. This
       //   system.theme.data state will go away entirely as soon as themes have
       //   a proper installation status.
diff --git a/core/lib/Drupal/Core/KeyValueStore/KeyValueFactory.php b/core/lib/Drupal/Core/KeyValueStore/KeyValueFactory.php
index 7edb754..a1aaa60 100644
--- a/core/lib/Drupal/Core/KeyValueStore/KeyValueFactory.php
+++ b/core/lib/Drupal/Core/KeyValueStore/KeyValueFactory.php
@@ -12,6 +12,8 @@
  */
 class KeyValueFactory {
 
+  protected $backend;
+
   /**
    * Instantiated stores, keyed by collection name.
    *
@@ -20,6 +22,17 @@ class KeyValueFactory {
   protected $stores = array();
 
   /**
+   * Constructs the key/value store factory.
+   *
+   * @param string $backend
+   *   The fully-qualified class name of backend implementing
+   *   KeyValueStoreInterface.
+   */
+  function __construct($backend) {
+    $this->backend = $backend;
+  }
+
+  /**
    * Constructs a new key/value store for a given collection name.
    *
    * @param string $collection
@@ -30,7 +43,7 @@ class KeyValueFactory {
    */
   public function get($collection) {
     if (!isset($this->stores[$collection])) {
-      $this->stores[$collection] = new DatabaseStorage($collection);
+      $this->stores[$collection] = new $this->backend($collection);
     }
     return $this->stores[$collection];
   }
diff --git a/core/modules/config/lib/Drupal/config/Tests/ConfigInstallTest.php b/core/modules/config/lib/Drupal/config/Tests/ConfigInstallTest.php
index 5efecd0..b549119 100644
--- a/core/modules/config/lib/Drupal/config/Tests/ConfigInstallTest.php
+++ b/core/modules/config/lib/Drupal/config/Tests/ConfigInstallTest.php
@@ -23,7 +23,6 @@ public static function getInfo() {
 
   function setUp() {
     parent::setUp();
-    $this->installSchema('system', 'system');
 
     // Ensure the global variable being asserted by this test does not exist;
     // a previous test executed in this request/process might have set it.
diff --git a/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php
index 116bb05..4935038 100644
--- a/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php
@@ -22,10 +22,6 @@
  *
  * @see DrupalUnitTestBase::$modules
  * @see DrupalUnitTestBase::enableModules()
- *
- * By installing the {system} schema, modules may be fully installed, too.
- *
- * @see DrupalUnitTestBase::installSchema()
  */
 abstract class DrupalUnitTestBase extends UnitTestBase {
 
@@ -37,6 +33,13 @@
    * this property. The values of all properties in all classes in the hierarchy
    * are merged.
    *
+   * Unlike UnitTestBase::setUp(), any modules specified in the $modules
+   * property are automatically loaded and set as the fixed module list.
+   *
+   * Unlike WebTestBase::setUp(), the specified modules are loaded only, but not
+   * automatically installed. Modules need to be installed manually, if needed.
+   *
+   * @see DrupalUnitTestBase::enableModules()
    * @see DrupalUnitTestBase::setUp()
    *
    * @var array
@@ -55,25 +58,41 @@
    */
   private $moduleList = array();
 
+  private $moduleFiles;
+  private $themeFiles;
+  private $themeData;
+
   /**
    * Sets up Drupal unit test environment.
    *
-   * Unlike UnitTestBase::setUp(), any modules specified in the $modules
-   * property are automatically loaded and set as the fixed module list.
-   *
    * @see DrupalUnitTestBase::$modules
    * @see DrupalUnitTestBase
    */
   protected function setUp() {
     global $conf;
 
+    // Copy/prime extension file lists once to avoid filesystem scans.
+    if (!isset($this->moduleFiles)) {
+      $this->moduleFiles = state()->get('system.module.files') ?: array();
+      $this->themeFiles = state()->get('system.theme.files') ?: array();
+      $this->themeData = state()->get('system.theme.data') ?: array();
+    }
+
     parent::setUp();
 
     // Provide a minimal, partially mocked environment for unit tests.
     $conf['lock_backend'] = 'Drupal\Core\Lock\NullLockBackend';
-    $conf['cache_classes'] = array('cache' => 'Drupal\Core\Cache\NullBackend');
-    $this->container->register('config.storage', 'Drupal\Core\Config\FileStorage')
+    $conf['cache_classes'] = array('cache' => 'Drupal\Core\Cache\MemoryBackend');
+    $this->container
+      ->register('config.storage', 'Drupal\Core\Config\FileStorage')
       ->addArgument($this->configDirectories[CONFIG_ACTIVE_DIRECTORY]);
+    $this->container
+      ->register('keyvalue', 'Drupal\Core\KeyValueStore\KeyValueFactory')
+      ->addArgument('Drupal\Core\KeyValueStore\MemoryStorage');
+
+    state()->set('system.module.files', $this->moduleFiles);
+    state()->set('system.theme.files', $this->themeFiles);
+    state()->set('system.theme.data', $this->themeData);
 
     // Ensure that the module list is initially empty.
     $this->moduleList = array();
@@ -109,20 +128,15 @@ protected function installSchema($module, $table) {
    *
    * Callbacks invoked by module_enable() may need to access information
    * provided by info hooks of the new modules already. However, module_enable()
-   * enables the new modules in {system} only, but that has no effect, since we
-   * are operating with a fixed module list.
-   *
-   * The {system} table is required to install new modules. Install it via:
-   * @code
-   *   $this->installSchema('system', 'system');
-   * @endcode
+   * enables the new modules in the system.module configuration only, but that
+   * has no effect, since we are operating with a fixed module list.
    *
    * @param array $modules
    *   A list of modules to enable.
    * @param bool $install
    *   (optional) Whether to install the list of modules via module_enable().
-   *   Defaults to TRUE. Requires the {system} table to exist. If FALSE, the new
-   *   modules are only added to the fixed module list and loaded.
+   *   Defaults to TRUE. If FALSE, the new modules are only added to the fixed
+   *   module list and loaded.
    *
    * @todo Remove this method as soon as there is an Extensions service
    *   implementation that is able to manage a fixed module list.
@@ -130,7 +144,7 @@ protected function installSchema($module, $table) {
   protected function enableModules(array $modules, $install = TRUE) {
     // Set the modules in the fixed module_list().
     foreach ($modules as $module) {
-      $this->moduleList[$module] = drupal_get_path('module', $module);
+      $this->moduleList[$module]['filename'] = drupal_get_filename('module', $module);
     }
     module_list(NULL, $this->moduleList);
 
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index bb3f2b4..1cc16c3 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -2821,8 +2821,8 @@ function system_rebuild_module_data() {
     $files = array();
     ksort($modules);
     // Add name, status, weight, and schema version.
-    $enabled_modules = config('system.module')->get('enabled');
-    $disabled_modules = config('system.module.disabled')->get();
+    $enabled_modules = (array) config('system.module')->get('enabled');
+    $disabled_modules = (array) config('system.module.disabled')->get();
     $all_modules = $enabled_modules + $disabled_modules;
     foreach ($modules as $module => $record) {
       $record->name = $module;
@@ -2994,7 +2994,7 @@ function system_rebuild_theme_data() {
   //   based on the current config. Remove this code when themes have a proper
   //   installation status.
   // @see http://drupal.org/node/1067408
-  $enabled_themes = config('system.theme')->get('enabled');
+  $enabled_themes = (array) config('system.theme')->get('enabled');
   $files = array();
   foreach ($themes as $name => $theme) {
     $theme->status = (int) isset($enabled_themes[$name]);