Development, like science, is a messy endeavor. It's near impossible to control all the variables. Testing code is a noble goal, but it's very easy to test the wrong thing. Many experienced scientists are fooled by their senses and biases. To account for that they crafted and refined a Scientific Method. That method has been stress tested by centuries of experimentation, discovery and peer-review. It probably wouldn't hurt to try to apply it to development and see what it can offer.