Migrated tests to XCTest

* Using a modern XCTest engine to run tests.
* Added some failure descriptions instead of "nil"

A few failures have been reported
![screen shot 2013-12-20 at 3 42 20 pm](https://f.cloud.github.com/assets/396451/1790660/94862716-697c-11e3-9f02-171f6aa05680.png)