Two weeks ago, I wrote an article in hack.guides() about testing with the Spock Framework and using Behavior-Driven Development (BDD).
Yesterday, the article was published in the main page (it was in review). You can find it here.
I think the Spock framework (and BDD) is the best option to create unit tests and you should at least, check it out.
As always, if I can help you in any way, don’t hesitate to contact me.