I used to read a lot of SF short-story collections from the local library as a kid, and this one has really stuck in my mind, but I've never been able to re-discover it as I can't remember the name or the author.
I would have read it in the 80s but it could be a lot older than that.
Story sort of reads like a set of instructions and the 'reader' (after a portal opens up) is forced to go through a series of increasingly dangerous set of trials on alien worlds.
The tone of the story is darkly comical, as the 'instruction book' gives survival odds out and compares human results with other aliens with differing anatomy and such.
I have a vague recollection that the final test is against some kind of killer robot and that only 2 or 3 other 'test subjects' have ever gotten that far.
I also seem to remember it was very short (10 pages).
Sorry to be so very vague, but if anyone out there could identify this, I would be grateful!