If you're interested in getting started with unit testing for embedded applications and you'd like to read an excellent tutorial, you should check out this post by Dmitry Frank. It'll walk you through installing and configuring Ceedling (and therefore Unity and CMock) and through tests for a small example. It's well thought out and a good read.
Dmitry is a talented engineer from Russia. He's worked on a variety of embedded projects, including his own preemptive RTOS which has been used in the wild. You can learn more about him at his website.