It depends on the stage of your company and product, which I think of as a continuum: on the far right is banking software, life support machines, and airline c

It depends on the stage of your company and product, which I think of as a continuum: on the far right is banking software, life support machines, and airline code; on the far left are prototypes and fun hacks. The amount of testing you do should depend on where on that continuum your project lies. Let's say it's a scale from 1 to 10: 1 being no testing, 10 meaning hardcore static analysis and tests for your test's tests). Life support machines are 10, as are aircraft, and please god the software in my car. Most projects start at 1, become roughly 3 in the early stages, and settle on 6 when they become more mature. Using the wrong level at the wrong stage is a recipe for disaster. No tests for your mature product instils fear of change - anything you do will likely break something, and you will have no warning about it. But writing lots of tests for your prototype will kill your productivity.