Matt Sparks has posted the latest tutorial in his "Building a PHP framework" series of posts. In this latest article he covers the use of test-driven development during the development of some of the first framework code.

In part 4 we laid the foundation for Analyze. Now it’s time to write the very first lines of code! [...] Essentially, test driven development is a process of writing tests before writing any code, then writing code that passes the tests. [...] If you’re new to TDD, this probably seems pretty weird. Stick with me.

He starts with a brief definition of what test-driven development (TDD) is and what tool he'll be using to create the tests. Next is a simple example of a test that creates a class instance (NumberAdder) and calls an add method on it. This fails because none of this exists yet, hence the "test first" part of TDD. He then goes back and creates the class and method and loads them so the test can use them.