When I was hired at my current job, I was given the National League of Nursing's Medication Test. 70 questions, took about an hour. Basic calculations, drug effects, classifications, the usual stuff.
The website with test plans is here: http://www.nln.org/testprods/pas_medadmin.htm
At my facility, it was used after a hiring decision, and then if you didn't get above 90% you got a take home remediation to work on for a couple weeks. Don't know how other facilities do it.
There were some things that I'd never heard of, but mostly stuff that you learn in nursing school. Do some brush up through your pharmacology text.