Evaluate the use of a mock REST server to simulate communication with the Twitter API

I found those post that might be helpful:
- Testing using mock module I guy trying to do the same as (or similar to) what we are trying to do in the Twitter DrupalContribute.
- #785362: Create more extensive guidelines for "mock module" creation and style
- #786156: Update the SimpleTest tutorial to reflect the 'mock module' pattern.

I also recommend to check the Services module. Not only because its a good example on how to do this with a mock module (see tests dir of the module), despite it does in other way that the one presented in Mock Web Service for Simpletest, also because it could be good to use its API to interact with other systems. As a matter of fact, its 4th version is going to be the starting point of web services API in core of D8 (read: http://www.garfieldtech.com/blog/web-services-initiative ("The road ahead" point)). This last point might be more appropriate in future versions of Twitter module.

Cheers,
Alessandro Mascherpa.