I'm not sure they're there yet, but there are some things about this that really appeal to me. Perhaps most notably is the fact that they are using a document as the data source for a test suite. While you document a requirement, you're also coding an automated test suite for the requirement. I've always liked the idea of "executable requirements", though it lives in my (and others') mind as an ideal, and I have yet to see it really implemented. Unfortunately, it looks like you still have to write actual code to accompany each set of test cases you create, but I'll consider the jury to be out until I see Dave's Ruby version. I haven't thought too much about it yet, but deep inside I want to believe that there is a way to create a framework that would enable this kind of thing with no coding required.
At any rate, I'm glad to see some movement in this area. And it's got me thinking a lot about other opportunities for executable documentation.