About ten months ago I managed to put Rhino Mocks (version 2.3.3) at 100% testability. That was the last time that I checked this, and since them I had many releases.
I checked it today, out of curiosity if nothing else, and I was surprised to discover that I still got an absurdly high level of tested code, 95% of Rhino Mocks are tested. The rest of the 5% are utility methods and the like, which I’m not going to worry much about.
The last change I did involved changing the way Rhino Mocks created mocks. This is about as important a change as you can make. This amount of testing gives me the ability to make a significant change to Rhino Mocks and still be certain that I am not breaking anything when I do it.