add unit test to verify that the store updated signal actually fired. Also fix bug where cloning item doesn't update the inherited metadata caches

common/lib/xmodule/xmodule/modulestore/mongo.py

@@ -537,6 +537,7 @@ class MongoModuleStore(ModuleStoreBase):
         Clone a new item that is a copy of the item at the location `source`
         and writes it to `location`
         """
+        item = None
         try:
             source_item = self.collection.find_one(location_to_query(source))
 
@@ -568,7 +569,6 @@ class MongoModuleStore(ModuleStoreBase):
                 course.tabs = existing_tabs
                 self.update_metadata(course.location, course._model_data._kvs._metadata)
 
-            return item
         except pymongo.errors.DuplicateKeyError:
             raise DuplicateItemError(location)
 
@@ -576,6 +576,8 @@ class MongoModuleStore(ModuleStoreBase):
         self.refresh_cached_metadata_inheritance_tree(Location(location))
         self.fire_updated_modulestore_signal(get_course_id_no_run(Location(location)), Location(location))
 
+        return item
+
     def fire_updated_modulestore_signal(self, course_id, location):
         if self.modulestore_update_signal is not None:
             self.modulestore_update_signal.send(self, modulestore=self, course_id=course_id,