Android Unit Testing for ActionBarActivity

I have a question regarding Unit Testing. I am messing around with my application and I want to include unit testing to the development process. I use ActionBarActivity's but the problemn is: where do I start? There are a lot of resources but I see different testing libraries, different ways of setting up the testing structure and for the 1,5 days that I have spent on learning and investigating the revenue is close to zero.

Basically, my question: Unit Testing on Android (with ActionBarActivity's): where to start?

Ps. I'm using Android Studio.

Thanks in advance.