diff -u b/core/modules/simpletest/simpletest.module b/core/modules/simpletest/simpletest.module
--- b/core/modules/simpletest/simpletest.module
+++ b/core/modules/simpletest/simpletest.module
@@ -419,6 +419,9 @@
  * each module for files matching the PSR-0 standard. Once loaded the test list
  * is cached and stored in a static variable.
  *
+ * @param string $module
+ *   Name of a module. If set then only tests belonging to this module is
+ *   returned.
  * @return
  *   An array of tests keyed with the groups specified in each of the tests
  *   getInfo() method and then keyed by the test class. An example of the array
@@ -435,16 +438,19 @@
  *   @endcode
  */
 function simpletest_test_get_all($module = NULL) {
-  $groups = &drupal_static(__FUNCTION__);
+  $all_groups = &drupal_static(__FUNCTION__);
+  $cid = "simpletest:$module";
 
-  if (!$groups) {
+  if (!isset($all_groups[$cid])) {
+    $all_groups[$cid] = array();
+    $groups = &$all_groups[$cid];
     // Make sure that namespaces for disabled modules are registered so that the
     // checks below will find them.
     simpletest_classloader_register();
 
     // Load test information from cache if available, otherwise retrieve the
     // information from each tests getInfo() method.
-    if ($cache = cache()->get('simpletest')) {
+    if ($cache = cache()->get($cid)) {
       $groups = $cache->data;
     }
     else {
@@ -453,6 +459,7 @@
       $module_data = system_rebuild_module_data();
       $all_data = $module_data + system_rebuild_theme_data();
       $all_data += drupal_system_listing('/\.profile$/', 'profiles', 'name');
+      // If module is set then we keep only that one module.
       if (isset($module)) {
         $all_data = array(
           $module => $all_data[$module],
@@ -504,8 +511,8 @@
           }
           // If this test class requires a non-existing module, skip it.
           if (!empty($info['dependencies'])) {
-            foreach ($info['dependencies'] as $module) {
-              if (!isset($module_data[$module])) {
+            foreach ($info['dependencies'] as $dependency) {
+              if (!isset($dependency_data[$dependency])) {
                 continue 2;
               }
             }
@@ -523,10 +530,10 @@
 
       // Allow modules extending core tests to disable originals.
       drupal_alter('simpletest', $groups);
-      cache()->set('simpletest', $groups);
+      cache()->set($cid, $groups);
     }
   }
-  return $groups;
+  return $all_groups[$cid];
 }
 
 /**
@@ -729,8 +736,9 @@
 /**
  * Get PHPUnit Classes
  *
- * @param bool $name_only
- *  If TRUE, returns a flat array of class names only.
+ * @param string $module
+ *   Name of a module. If set then only tests belonging to this module is
+ *   returned.
  */
 function simpletest_phpunit_get_available_tests($module = NULL) {
   // Try to load the class names array from cache.