PhpSpec is a toolset for building out testable pieces of functionality strictly designed to meet (and only meet) the project requirements that you have made explicit. Identify your inputs, test your expected outputs. That's it.
Wait! Don't go. This is not a look-at-this-cool-tool talk. This is a live identity crisis, with a demo. How do we as developers mature our skills and deliver testable, functional code while we continue to work on Drupal 7?
Talking through that question includes: