I am all for high test coverage. One should not underestimate the effort in that, though. Some time ago I covered some two thousand lines of code completely in

I am all for high test coverage. One should not underestimate the effort in that, though. Some time ago I covered some two thousand lines of code completely in tests. As in, all code paths, checking all side effects. Kind of an effort in the spirit of "dealing effectivly with legacy code" by Michael Feathers. They were quite non-trivial and it took me about two months. Doing such a thing may not always be feasible. Also if code is written by others they may have covered fewer code paths in tests than one would have liked. A type checker will check all code paths but the tests that your predecessor failed to write are not checking anything.