EDIT: Even though this article was written for RestKit 0.9 with the Object Mapper 1.0, it works with RestKit 0.9 and the Object Mapper 2.0.
I recently had troubles with unit testing an iOS application which rely in RestKit and CoreData.
Since I didn't find a clear solution on the web, I share in this article how I solved this issue. It is, in fact, simpler that It may seem.
Note that for my unit tests, I use the SenTestKit framework provided by Apple with XCode4.