什么时候应该停止单元测试

I can often identify plenty of areas which are nicely encapsulated and easily unit tested, but I also find that a lot of code where unit testing doesn't really seem to work as well - typically data access and user interface. No matter what unit testing "techniques" I try I tend to find that in these places it's not only a lot of effort to create functioning unit tests, but these tests tend to be very fragile and don't really test very much.I can often identify plenty of areas which are