> if he spent barely 20 minutes writing 3–4 trivial unit tests for this function, we would have saved probably 6 hours each ... The math was beyond simple. 20 mins invested and 12 hours saved.<p>I've heard this reasoning before. The math is simple but wrong. The cost of writing unit tests must also include the time spent on tests of stuff that was never broken; and for the maintenance of tests that break because of new features or bug fixes rather than actual code issues.<p>Unit tests are very useful, essential, in some situations. In others they're a waste of everybody's time.