[simonw]

Yeah, but in my experience it really is a literal today vs tomorrow thing.

Your tests pay for themselves the moment you want to ship a second feature without fear of breaking the first.

[Ekaros]

If you are going to test what you develop might as well write any tests you do formally right away. It is unlikely you get it fully ready in one go, so you need to anyway run same tests again when you iterate it developing it today.

And that is the minimum level to aim at. If you can automate anything you do to test it right now you should.