I think "idiot" is a little harsh. You can definitely be too earnest in writing unit tests, but I think there are places in almost any program that would benefit from them. For example, in a GUI app chances are you have some sort of model of the data; tests could help ensure that the model is well behaved. This way, if you have an odd GUI glitch you can be confident it's actually in the GUI code rather than in the data underlying the interface.