In a new post today, Padraic Brady asks the community for any kind of input as to what they've seen for behaviour-driven development in PHP:

Behavior-Driven Development (BDD) is an evolution of Test-Driven Development (TDD) which pushes the focus away from the concept of testing to one of specifying behaviours in a form more easily understood.

In asking about any of the tools that might happen to be out there, he also gives an example (from a Ruby perspective) on how the behaviour-driven method is put into practice. The code describes the behaviour by what "it should" do and evaluates based on that.