Distinguishing between specific error values and types is easy in Go, thanks to the (relatively) new errors.Is and errors.As functions. Let’s talk about what they do, when and how to use them, and how to know which one is appropriate.
All tagged sentinel error
Comparing Go error values
Usually what matters about an error is that it’s not nil, but what if we want to know whether it’s some specific error value? For example, in a test? Let’s look at some of the right and wrong ways to do that.