This. It's not that tests have no benefit -- they do, especially for complex refactoring (though even for that, as you say, tests are rarely exhaustive enough t

This. It's not that tests have no benefit -- they do, especially for complex refactoring (though even for that, as you say, tests are rarely exhaustive enough to engender full trust). But outside of the narrow confines of production programming, it's rare that the requirements can be specified completely up-front. In the initial stages of development, coding is very much a discovery process. Code is often evolved rapidly and drastically, such that any test written is a throwaway. And some of these tests/mocks aren't easy to generate. In data intensive applications, it's especially a chore to have to generate new mock database objects each time the code changes, and with completely different data characteristics to boot (in order to test different facts of the code). The psychological tedium of doing this will put off most developers. The potential drag on productivity extends to more than just the time required to write test + code: the whole pace will feel sluggish and the dev is liable to feel demotivated. I see tests being more useful as a retrospective addition, once the code has stabilized and the use-patterns established.