On the CodingItWrong site Josh Justice has written up an interesting article about the different "schools" of testing and the approaches they take. While it's not specific to PHP testing, a lot of the principles still apply.

The last few months have been my first opportunity to do automated testing at my full-time job. As I’ve been trying to get the hang of it, my biggest question has been how many of each type to test to write: how many unit, integration, and acceptance tests. Turns out Folks Got Opinions™ on this! As I researched, I found at least four different approaches to testing, and they each provide different answers to a number of questions I had.

His research answered questions about what the different types are, what processes are used to create tests and what to check for. He also answered question about how to change code based on what you find during testing and what "good code" is. HE then breaks down the rest of the article into the four different types of software testing he found during his research:

• Test Approach #1: Whatever it is DHH does.
• Test Approach #2: Classical TDD
• Test Approach #3: Mockist TDD
• Test Approach #4: Discovery Testing

Each sections includes a summary of the testing practices, links to some other resources on the topic and an illustration of the typical flow when writing the tests.