I wasn't implying to you that you don't work on large PHP projects. It was directed at the creator of this forum topic. Sorry for the misunderstanding. What I meant is that I doubt the creator of this topic is working on massive project, big enough to warrant the use of a debugger. And I most certainly do not deny that there are huge PHP projects out there. A company I worked for that provided SMS gateway services had a HUGE project that had been in the works for 5 or so years. And that was a lot of code.
If one minds their code and thinks 5 steps ahead, a debugger is never needed. Php follows simple rules, Follow the rules to the max and you will have no bugs.The ones you have you find when trying the site out, hence beta testing.
To the original poster: There are not many tools for php testing - there are very few capable of creating automatic test cases and/or mutation testing. However you could start with PHPUnit and perhaps the Zend IDE which allows a simple way to run tests and suites.