I just got on a new project and am trying from the get-go to structure all my code so that it's easily testable. Academically, that is a no-brainer. In practice, though, some chunks of code are more difficult to structure so that they're easily testable. Towards that end, I've been pushing System.IO.Abstractions again. And, to get that going I decided it was time to refresh my examples. In the code below, we see how injecting the file system into the repository ultimately allows us to write testable code. If structured correctly, then our repository requires no subsequent refactoring to run in a unit test environment versus a "real" environment even when dealing with something like the file system. Let's take a look at our code. The Console Application The console application is straightforward. We have a private method (at the bottom) that assembles and returns a mock file system. Next, we perform the following steps: We feed that mock file system