I wanted to write something like this for a long time. Now I don’t have to – Peter Gillard-Moss did it much better. One of the things I really like in Isolator is that you don’t need to sacrifice your design for testability. It doesn’t mandate use of factories or dependency injection. You can use those, but you don’t have to.
What happens when you decide go whole hog the other way in the name of good design? Go read Peter’s post on his experience going the “right” way. And then returning to the land of the sane.