I deal with this at work. The code has never been refactored. There are unit tests for some areas but the views and controllers have so many lines of code and so many unneeded branches that attempting a test there is near impossible now. As soon as I came to the team I've managed to accomplish two minoir refactoring jobs in small areas of the code. I've pitched a more major refactor to the team and now we just need to get it passed our manager.

My own projects generally lack extensive testing (and the code lacks complex code paths) but I refactor heavily.