Probably...

In most cases, I just “try it and see.”   If you want to see if the current-user can create a file somewhere ... try to do it.   Using a “junk” filename, try to create it (using some system-command like e.g. touch, in a qx// block), and then immediately remove it (same way).   Wrap the whole thing in an eval block.   If an error is thrown (“$@” is non-blank), you know it didn’t work.   Yeah, it’s a hack, but it works reliably when a lot of other things don’t.

There are so many things that can affect file-access, that it is often much more difficult to “guess,” than to simply “push on the gate and see if an alarm goes off.”