There is an existing project that is already deployed in production. We want to add some tests on it (the sooner the better) and I have to choose between going the BDD way (rspec/cucumber) or the TDD way (TestUnit). I am really starting with BDD and I am wondering what could be the best decision to take? I am affraid that using rspec/cucumber on an existing rails project (which was deployed this week and requires really fast iterations) will be quite hard to do (especially that it is not supposed to be used this way, I mean we are supposed to write stories/features first and iterate from there).
TestUnit could be more reasonable, may be.
Do you have any thoughts on that? An experience to share? Some advices?