Sebastian Bergamnn points out an article he's written in the latest issue of the German publication "PHP Magazin" covering PHPUnit3 (cover story, no less).

PHP has grown from a niche language where one could only originally add a bit of dynamic functionality to a page to a powerful tool, which is being used more and more in the development of business-critical applications. This enterprise level of business logic has to work correctly all of the time, so how do you guarantee it will? Through testing, of course.

Sebastian covers some of the contents of the article, including what unit testing is, how to write some sample tests, and brief looks at things like code coverage, mock objects, and PHPUnit's integration with Selenium RC.