diff --git a/modules/block/block.test b/modules/block/block.test
index 9639b2c106962ccf6887541958f487809a5ae595..323034062d3f3659dc007df1342ca58db30bac41 100644
--- a/modules/block/block.test
+++ b/modules/block/block.test
@@ -764,6 +764,10 @@ class BlockHiddenRegionTestCase extends DrupalWebTestCase {
     );
   }
 
+  function setUp() {
+    parent::setUp(array('block_test'));
+  }
+
   /**
    * Tests that hidden regions do not inherit blocks when a theme is enabled.
    */
diff --git a/modules/block/tests/block_test.module b/modules/block/tests/block_test.module
index 2abc433c98240b6c409ed10a3e27b920e8c154b0..5e06d5cf51f2216b0649c0893721f9cb8429179f 100644
--- a/modules/block/tests/block_test.module
+++ b/modules/block/tests/block_test.module
@@ -5,6 +5,14 @@
  *   Provide test blocks.
  */
 
+/**
+ * Implements hook_system_theme_info().
+ */
+function block_test_system_theme_info() {
+  $themes['block_test_theme'] = drupal_get_path('module', 'block_test') . '/themes/block_test_theme/block_test_theme.info';
+  return $themes;
+}
+
 /**
  * Implements hook_block_info().
  */
diff --git a/themes/tests/block_test_theme/block_test_theme.info b/modules/block/tests/themes/block_test_theme/block_test_theme.info
similarity index 100%
rename from themes/tests/block_test_theme/block_test_theme.info
rename to modules/block/tests/themes/block_test_theme/block_test_theme.info
diff --git a/themes/tests/block_test_theme/page.tpl.php b/modules/block/tests/themes/block_test_theme/page.tpl.php
similarity index 100%
rename from themes/tests/block_test_theme/page.tpl.php
rename to modules/block/tests/themes/block_test_theme/page.tpl.php
diff --git a/modules/simpletest/tests/theme.test b/modules/simpletest/tests/theme.test
index ea0f257dd380d9727d8c6ed73c5254e20ada5dd1..d548850990be7068141c50d752cd96ec0dd45638 100644
--- a/modules/simpletest/tests/theme.test
+++ b/modules/simpletest/tests/theme.test
@@ -9,6 +9,8 @@
  * Unit tests for the Theme API.
  */
 class ThemeUnitTest extends DrupalWebTestCase {
+  protected $profile = 'testing';
+
   public static function getInfo() {
     return array(
       'name' => 'Theme API',
diff --git a/modules/simpletest/tests/theme_test.module b/modules/simpletest/tests/theme_test.module
index 160d192dd82a565858bdafc82dab953b2b952ef9..9cec5381d23ccf87bb90fac5e4963fde65e10b46 100644
--- a/modules/simpletest/tests/theme_test.module
+++ b/modules/simpletest/tests/theme_test.module
@@ -1,5 +1,13 @@
 <?php
 
+/**
+ * Implements hook_system_theme_info().
+ */
+function theme_test_system_theme_info() {
+  $themes['test_theme'] = drupal_get_path('module', 'theme_test') . '/themes/test_theme/test_theme.info';
+  return $themes;
+}
+
 /**
  * Implements hook_menu().
  */
diff --git a/themes/tests/test_theme/template.php b/modules/simpletest/tests/themes/test_theme/template.php
similarity index 100%
rename from themes/tests/test_theme/template.php
rename to modules/simpletest/tests/themes/test_theme/template.php
diff --git a/themes/tests/test_theme/test_theme.info b/modules/simpletest/tests/themes/test_theme/test_theme.info
similarity index 100%
rename from themes/tests/test_theme/test_theme.info
rename to modules/simpletest/tests/themes/test_theme/test_theme.info
diff --git a/modules/system/system.api.php b/modules/system/system.api.php
index f241eea7857956d0f9264455cd89936825e43b1b..e2fe6c61950bda1408daf1212a5398b916ac6781 100644
--- a/modules/system/system.api.php
+++ b/modules/system/system.api.php
@@ -1906,6 +1906,25 @@ function hook_module_implements_alter(&$implementations, $hook) {
   }
 }
 
+/**
+ * Return additional themes provided by modules.
+ *
+ * Only use this hook for testing purposes. Use a hidden MYMODULE_test.module
+ * to implement this hook. Testing themes should be hidden, too.
+ *
+ * This hook is invoked from _system_rebuild_theme_data() and allows modules to
+ * register additional themes outside of the regular 'themes' directories of a
+ * Drupal installation.
+ *
+ * @return
+ *   An associative array. Each key is the system name of a theme and each value
+ *   is the corresponding path to the theme's .info file.
+ */
+function hook_system_theme_info() {
+  $themes['mymodule_test_theme'] = drupal_get_path('module', 'mymodule') . '/mymodule_test_theme/mymodule_test_theme.info';
+  return $themes;
+}
+
 /**
  * Alter the information parsed from module and theme .info files
  *
diff --git a/modules/system/system.module b/modules/system/system.module
index 46ec87db1f1048d5ff23d9d55a2fdd30263cf03a..eac76a33d5e58043896e727f7911f2b244352c82 100644
--- a/modules/system/system.module
+++ b/modules/system/system.module
@@ -2472,6 +2472,18 @@ function _system_update_bootstrap_status() {
 function _system_rebuild_theme_data() {
   // Find themes
   $themes = drupal_system_listing('/^' . DRUPAL_PHP_FUNCTION_PATTERN . '\.info$/', 'themes');
+  // Allow modules to add further themes.
+  if ($module_themes = module_invoke_all('system_theme_info')) {
+    foreach ($module_themes as $name => $uri) {
+      // @see file_scan_directory()
+      $themes[$name] = (object) array(
+        'uri' => $uri,
+        'filename' => pathinfo($uri, PATHINFO_FILENAME),
+        'name' => $name,
+      );
+    }
+  }
+
   // Find theme engines
   $engines = drupal_system_listing('/^' . DRUPAL_PHP_FUNCTION_PATTERN . '\.engine$/', 'themes/engines');
 
diff --git a/themes/tests/update_test_basetheme/update_test_basetheme.info b/modules/update/tests/themes/update_test_basetheme/update_test_basetheme.info
similarity index 100%
rename from themes/tests/update_test_basetheme/update_test_basetheme.info
rename to modules/update/tests/themes/update_test_basetheme/update_test_basetheme.info
diff --git a/themes/tests/update_test_subtheme/update_test_subtheme.info b/modules/update/tests/themes/update_test_subtheme/update_test_subtheme.info
similarity index 100%
rename from themes/tests/update_test_subtheme/update_test_subtheme.info
rename to modules/update/tests/themes/update_test_subtheme/update_test_subtheme.info
diff --git a/modules/update/tests/update_test.module b/modules/update/tests/update_test.module
index 4acb6ef837e605af25927aa7aeda03fea82212de..e7ee43eecf2eb5bee9cfbee201675fb734d1067b 100644
--- a/modules/update/tests/update_test.module
+++ b/modules/update/tests/update_test.module
@@ -1,5 +1,14 @@
 <?php
 
+/**
+ * Implements hook_system_theme_info().
+ */
+function update_test_system_theme_info() {
+  $themes['update_test_basetheme'] = drupal_get_path('module', 'update_test') . '/themes/update_test_basetheme/update_test_basetheme.info';
+  $themes['update_test_subtheme'] = drupal_get_path('module', 'update_test') . '/themes/update_test_subtheme/update_test_subtheme.info';
+  return $themes;
+}
+
 /**
  * Implements hook_menu().
  */
diff --git a/themes/tests/README.txt b/themes/tests/README.txt
deleted file mode 100644
index 5ddaa8caf22eedc2dc5e854f695b4a89614710ad..0000000000000000000000000000000000000000
--- a/themes/tests/README.txt
+++ /dev/null
@@ -1,4 +0,0 @@
-
-The themes in this subdirectory are all used by the Drupal core testing
-framework. They are not functioning themes that could be used on a real site
-and are hidden in the administrative user interface.