[ionrock]

It is really a chicken and egg problem. On the one hand, it would be good to refactor the code to help write some tests. On the other hand, you really shouldn't refactor the code with tests to prove that you haven't broke anything. In either case, you are correct that it can be extremely difficult.

While there is no easy answer, I've found that in these situations, I still try to write a test first. The difference being that I try to write a test that exercises the code at some API level that I don't want to break. These test start off really ugly and require a ton of work, but they ensure that refactoring the lower level code to make it more testable doesn't break things. Eventually, the tests and code at the higher level can be updated safely.