There is a little script I started using called PHPUnit. There are a bunch of <Language>Unit testing programs. The popular ones are CppUnit, NUnit, AnyUnit, and JUnit. PHPUnit is a great unit testing tool for PHP scripts to make sure everything is performing as expected. This is especially handy when you have big projects. You can stub functions to make sure they work before spending all that time and getting an error somewhere. Then you have to trace the control path to find out where it's coming from. This makes it a whole lot easier.
http://sourceforge.net/projects/phpunit/
