I've never had to take a pre-employment medication test. For one thing, by passing the state boards, you've already proven you know all the basic and general stuff, along with the basic math skills needed to calculate dosages and such.
For another thing, whichever unit you will be working will have a more specific set of commonly-used medications. You really can't know what those medications are until you start working there, unless perhaps the manager gives you a list to study.
I work on a combined ICU/telemetry floor. I work with many, many meds, and I know them forwards and backwards. When I encounter one that's unfamiliar to me, I do what everybody does: I look it up.
If you put me on an oncology floor or (god forbid) an OB floor, I would be helpless. I could not give pitocin without spending a good 15 minutes researching the basics, and I would not give it without the supervision of an experienced nurse. But if that OB nurse came to my floor- her worst nightmare too, I'm sure- I wouldn't expect her to be able to give the propofol or the diltiazem drips without study and supervision.
If I were in your position, I'd ask if this test is on general medication knowledge, like the NCLEX? or is it on medications specific to that unit? If it's the latter, I'd ask which meds I was expected to know so I could study.