For now I'm ignoring the story based approach to BDD, I still think it's probably going to be useful but I'm not sure I'm yet in a place where I can take advantage of it so I'm just going to focus on the specification style. Doing it this way is also simpler because in my view the specification based approach is just "better TDD" but the story based approach seems to me to be a bit more fundamental and affects more than the developers.
I've gone for this style of test class/method naming:
I'm enjoying naming tests in this sort of style, I've toyed with a few other approaches but this one has so far kept me happy as the class/test names are not too long but they are quite expressive.
I've taken out all the "should_" from the tests because it felt like noise especially when I viewed the list of test names in the IDE.
Of course this is very similar to the approach others have specified, including Agile Joe and there will certainly be better naming schemes around.
BDD (Astels Style)
Some seem to see BDD as primarily being about making it easy to trace a specification (test) back to its context. You start out with a context (small test fixture for a particular case) and then write your specifications, most of the code ends up in the test class setup method and the tests themselves are nice and small. You don't just end up with one big CustomerTest class full of tests that require different fixtures or which are for different features.
I do find that BDD's style of having lots of test classes (small fixtures) and attempting to have one line of code in the specification (test) method can make it easy to understand what is being specified.
It's not all good though, one of my colleagues points out that he likes to see all of the code in the test method.
We were also slightly worried by the fact that the specifications for a class end up fragmented across quite a few files, which is fine but you might have some fun finding the specification for behaviour for a particular class in a large code base. I'm getting around this at the minute by tagging the fixture classes with a [Concerning("AccountMapper")] as discussed by Agile Joe, you can then search for the class name and find all the specifications. Not very advanced though, but then again it will improve if tools come in that support the BDD style.
Oh and Brian Donahue has a post on the same sorts of issues so I'm not alone in think about this, and I'm sure they are issues that many other people are dealing with.
At the moment I'm not using any special framework for these specifications at the moment, which I think is a valid choice (for now). I'll probably look again at the specification side of NBehave and at SpecUnit.NET but it seems too early to be using either on commercial projects at the moment.
Initially my reaction was that this is really just TDD with a test class per fixture policy that focuses on really small fixtures. It hardly seems like a fundamental change, but having done it I think the combination of naming and small test fixtures is quite useful and could (perhaps) lead to people doing TDD "properly".
This is probably only interesting to a few people but there are issues with using these approaches in Team System. Nothing major but annoyances.
For example you cannot (as far as I can see) re-alias [TestMethod] to be [Specification]. Also the test list window is ridiculously constricting and there is (so far) no support for integrating other test runners into Team System.
There may be workarounds for some of these issues, for now I'm ignoring these topics though and just doing the best I can.