Sure. This is a good practice for multiple reasons. However, the code that glues my interface to the underlying I/O is still there and needs testing, right? I

Sure. This is a good practice for multiple reasons. However, the code that glues my interface to the underlying I/O is still there and needs testing, right? I agree with you in general. But it always feels like there are spots where a mock of some kind is the only way to cover certain things.