It’s been a bit since I’ve written on this blog about anything other than containers, but I’ve been reading a lot of new (to me) Go code lately and wanted to discuss unit testing. I’m pretty firmly in the camp that testing is critical for building reliable, maintainable systems, and unit testing is an important component of that (though I do not believe it is sufficient on its own; integration, functional, or end-to-end testing is also often just as important). Unit testing is a somewhat special form of testing though, since the goal is to test the smallest functional unit of a system. One tool used as a part of unit testing that has been popular for as long as I’ve been employed as a software engineer is that of a test double.