you do not need to modify fake py  you can simply pass a  methods  parameter to create one server to fake any method of a server object  and i think this command should be  os server add  floating ip in doc source commands rst  you can see add remove add some object to a container object  the command is built in the order of  container add object  container object the positional arguments appear in the same order here  server is the container  and floating ip is the object  i think i have done this in c so  maybe we do not need this patch 