Added some tests for autoDistribute methods

Just wanted to warm my feet on writing tests for autoDistribute methods. Also would be good to know a few things before starting:

* At the moment I check only view size. What would be the things that I should focus on for these methods? The fact that some constraints are added is already tested for I think, so just checking the frames?
* What's would the best way to minimise code duplication when checking frames for each view in the array? Looping/factoring out into different methods or just simply not worry and copy-paste?
* Should I have one test method for `autoDistribute withFixedSpacing` and another for `autoDistribute withFixedSize` or split them into several smaller test methods? What would be the logical parts to split it around?
* I guess more of a philosophical question, but how much testing would be enough in this case?