TCPHP

"The heart of SimpleTest is a testing framework built around test case classes."

PEAR has PHPUnit, a PHP unit testing package.

This is for java but has many good points about unit testing in general.

Would you like to help support open source and free software but aren't exactly familiar with the subtleties of C memory management? Cash always helps. Short of that, telling the developers how great they are goes a long way, but if you really want to be part of the team and learn something along the way, help by testing software. This not only helps make the software better, but lets you learn about the software and the community, sharpens your own development skills and improves your attention to detail. Testing is actually a lot of work if done right. This article tries to point you at projects that need testing.

Safari Bookshelf is an electronic reference library for programmers and IT professionals.

I recommend that everyone get on board for the 14 day free trial (be
sure to put a reminder in your calendar to cancel before the 14 days is
up so that you don't get flipped into a $19.99 monthly subscription
without your wanting it to).