On his site today Jani Hartikainen has a new post helping to demystify some potential confusion around unit testing, test-driven development and behavior-driven development. He's talking about them in the context of Javascript in this case, but the fundamentals transfer to just about any other language, including PHP.

When you’re just getting started with automating your JavaScript testing, there’s a lot of questions. You’ll probably see people talk about unit testing, TDD or Test-Driven Development, and BDD or Behavior-Driven Development. But which one of them is the best approach? Can you use all of them? I’ve talked to a number of JavaScript developers, and there seems to be some confusion about all this. So, let’s take a look at Unit testing, TDD and BDD, and fix some of the common misconceptions about them out there.

For each he provides an overview of this basic concepts and a bit of sample code showing it in action. For TDD (test-driven development) there's not really a way to show it specifically in code as it's more of a practice. Instead he gives a "checklist" to follow when practicing it.

Unit Testing gives you the what. Test-Driven Development gives you the when. Behavior Driven-Development gives you the how. Although you can use each individually, you should combine them for best results as they complement each other very nicely.