On NetTuts.com there's a new tutorial that wants to help you get started with a different sort of testing methodology than you might not have tried before - test driven development:

Let's admit it: the PHP community has lagged a bit, when it comes to advocating test-driven development. We know we should, but, even to this day, a sizable portion of the community does not. In this new series of videos and tutorials, created by the Nettuts+ team, we're hoping to change that. Trust me: it's not as tough as you think.

This first post in their series helps you get the environment set up (including Composer and PHPUnit) and test a basic class. It's a video, but there's links to the software you'll need to install at the end of the post.