I don't think it is that much different, just maybe in proportions. In pretty much every application I write there 2 types of code. There is the guts or busines

I don't think it is that much different, just maybe in proportions. In pretty much every application I write there 2 types of code. There is the guts or business logic that is written in the style of a library making it very testable. The other is the top level code, the 'main loop'. This is just there to hook together the library code in as short a way as possible. I think UI code differs in that it tends to have quite a bit more of this top level code that is basically un-testable except for very high level integration/scripted tests and QA testing. But UI code still has some amount of the library/logic code that can be written with testing in mine. I think this speaks to the myth that 100% test coverage is desirable and good. It is not.