Testing using mock module

Hi

I'm developing a module which uses twitter module to post tweets on certain account. Trying to develop in TDD way I'm writing bunch of testing functions. Everything was fine until I wanted to test behavior of my function which relies on methods defined in other module.

So is it possible to create a mock module in testing environment, with the same name as an existing one in production env., so when tested module calls

module_load_include('inc', twitter');

it will call my custom file used for testing only ?