errors

Sentinel Error

var invalidValueErr = errors.New("Invalid value for diagnosticv2 message")

Later use by "wrapping" it with additional details:

return fmt.Errorf("%w: %s topic", invalidValueErr, mtgext.CallNetwork)

Use in tests like:

func SomeTest() {
    err := updateCallNetwork("garbagestring")
    errors.Is(err, invalidValueErr) // returns true, don't need to rely on specific error strings
}

Summary:

• Not necessary for every error

• Useful if error is part of an API

• Useful to help testing

More info: https://go.dev/blog/go1.13-errors