Not arguing with you, Vince. I've never understood those either.
To the original suggestion: The easiest way to find out whether a directory is readable is to try reading it. The easiest way to find out whether it's writable is to try writing to it — e.g. try creating and deleting a temp file there. My first thought would be to write it as a function, which could then be used in IF, IF, etc. as desired.