[PaulKeeble]

Those that TDD a lot have come to realise what TDD does is help you find a good design. It teaches you something about the way in which you code and design and allows you to cheaply play with the alternatives. It also ensures the code works and ensures so in the future as you undergo changes.

BDD for functional testing ensures that the functionality you test works and again that before you cut code you have thought about how your functionality is going to work. These are valuable exercises to do with or without the code to run.

So when it comes to an MVP to test the idea how well does it have to work and how well does it have to be designed? Some amount of your system will be critical and if in the process of changing it you break that functionality you may have no product. A certain amount of confidence in the core of what you are building is important, having it automated will allow you to change quickly. Ensuring 100% code coverage is not important, some bugs when you are small are probably acceptable.