I routinely run into this problem, and I\'m not sure how to get past this hurdle. I really want to start learning and applying Test-Driven-Development (or BDD, or whatever) but
I see what you are saying, but eventually your models will become sufficiently advanced that they will require (or be greatly augmented by) automated testing. If not, what you are essentially developing is a spreadsheet which somebody has already developed for you.
Since you mentioned Rails, I would say doing a standard create/read/update/delete test is a good idea for each property, especially because your test should note permissions (this is huge I think). This also ensures that your migrations work as you expected them to.