diff -u b/core/modules/config/tests/config_test/config_test.module b/core/modules/config/tests/config_test/config_test.module
--- b/core/modules/config/tests/config_test/config_test.module
+++ b/core/modules/config/tests/config_test/config_test.module
@@ -13,10 +13,14 @@
   $GLOBALS['hook_config_import'] = __FUNCTION__;
 
   // This config object has been saved through the current module API.
+  // There is no guarantee that the module API uses $new_config directly,
+  // nor a hard requirement for configurable thingies to be based on Config
+  // objects. Therefore, mock these possible scenarios.
+  $config = config($name, $new_config->get());
   // Therefore, its version property should equal the current version.
-  $new_config->set('version', VERSION);
+  $config->set('version', VERSION);
 
-  $new_config->save();
+  $config->save();
   return TRUE;
 }