[dwaite]

Test driven development on one project would often save me weeks per bug fix.

This was because it maintained an environment where I could replicate portions of the business logic (as assembled modules) outside a production environment. This made it much easier to do analysis/fuzzing of one component of the system, vs trying to replicate and do post-mortem crash analysis on the entire deployed system.

But I clarify this is TDD, not unit tests. A development methodology where unit tests are wedged in after the fact do not promote the sort of modular programming needed to be able to do this.