On NETTUTS.com today there's a new tutorial to help you get started with effective test-driven development in your PHP applications with SimpleTest.

Testing your code is annoying, but the impact of not doing so can be orders of magnitude more annoying! In this article, we’ll use test-driven development to write and test our code more effectively.

They start with the basics - what test-driven development is, why it's a good idea and how the whole process works to improve your code. They opt for a bit simpler route for their testing tool and chose SimpleTest. They show you how to set it up and where to start. In order for TDD to work, you really have to plan out your application so you know what you're testing. They give you an example of a simple script and how to start from failing tests to a working app.