Introducing Fuel Continuous Testing. Basically what it does is monitor your project for php file changes and reruns your unit tests. Upon completion of unit tests it gives you feedback in growl fashion.
Here's the code https://github.com/keith-loy/fuel-continuous-testing
Installation and usage is explained in the README. I haven't been able to test with OS X, but it should work. I have it working in Linux Mint with Gnome Shell desktop.