>TDD on functional code that is mostly exchanging values between systems. All the stub and mock crap goes away since values become the boundary of the system.

>TDD on functional code that is mostly exchanging values between systems. All the stub and mock crap goes away since values become the boundary of the system. That's generally why I think functional programming is taking off. It's much easier to reason about input-output of stateless functions. They're much easier to test and develop. They're way easier to understand for the reader, because the reader can understand what's happening in one place, instead of having to look through many different files, creating a complex model of all the inheritance relationships between classes.