On the PHP in Action Blog, there's a this post that shares some tips for testing your web applications with some simple tests.

I just started listing the techniques I've learned when writing tests to exercise the web interface of a PHP application. This is from my experience and my personal preferences; it's not the final word or necessarily right for everyone.

He suggests:

• Use SimpleTest's Web tester if you can
• Test the web output using regular expressions
• Use element IDs or names to test links, forms and fields
• Log HTTP requests in the application