One of my coworkers and her husband run Gibson's Bookstore, in Concord, NH. When hiring new employees, each applicant is given a knowledge of literature test to see how well they'll do at reader's advisory.
Their opinion is that bookstore staff are first and foremost reading advisers, and cashiers and stockers second. The test questions cover a broad scope of literature, just like the questions of customers (and library patrons):
2) Name five characters invented by William Shakespeare.
13) What is Ender Wiggin famous for?
14) James and the Giant ________ by Roald _______.
23) Why do some Sneetches feel superior to others?
To get hired, applicants must get at least half of the questions right. Perhaps libraries could implement something similar? Perhaps they already do.
I also have a list of reference questions and tasks I give to reference staff after they've been hired, to help with training. It is based on something my director found (can't remember what or where), but I tailored it to get new staff familiar with the type of questions we get, our collection, our policies, basic tech support, and reference in general. They get it as a Word document, and work on it for their first few months.
Some people like tests and some don't. But each in their own way, I think these tests are valuable to make sure that the people interacting with the public are really able to help the public.