He is testing: testing that people want this. In the beginning your biggest risk is making something poeple don't want, not code that breaks.
Notch is creating right now, watch http://vimeo.com/36579366 "inventing on principle" which explains the importance of immediate visual feedback.
Also give him just a "little" credit for minecraft
I just dont want anyone else to think it is a good idea for them :-)
The tests can be the same or even better that those added at some TDD style.
And, in either case, that would be a nice problem to have.
And yes, it is a better problem to have, then to have code that noone wants.