diff -u b/core/includes/module.inc b/core/includes/module.inc
--- b/core/includes/module.inc
+++ b/core/includes/module.inc
@@ -74,6 +74,7 @@
   $list = $module_list;
 
   if (isset($fixed_list)) {
+    $module_list = array();
     foreach ($fixed_list as $name => $module) {
       drupal_get_filename('module', $name, $module['filename']);
       $module_list[$name] = $name;
diff -u b/core/modules/simpletest/lib/Drupal/simpletest/UnitTestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/UnitTestBase.php
--- b/core/modules/simpletest/lib/Drupal/simpletest/UnitTestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/UnitTestBase.php
@@ -49,11 +49,8 @@
     $conf = array();
     drupal_static_reset();
 
-    // Empty out module list.
+    // Enforce an empty module list.
     module_list(NULL, array());
-    // Prevent module_load_all() from attempting to refresh it.
-    $has_run = &drupal_static('module_load_all');
-    $has_run = TRUE;
 
     // Re-implant theme registry.
     // Required for l() and other functions to work correctly and not trigger