At my previous job, when hiring for vacant positions, we created a fairly basic test to go along with the interview. The test was intended to be very easy - just a "Can you handle the bare bones of the job" - something an undergrad should be able to complete without much trouble.
It was shocking how many people nailed their interviews (came off as confident, charismatic, competent), and then proceeded to completely bomb the test.
I don't care about either candidates interview skills at this point, but I'd sure be fascinated to see how they perform on a basic competency test with regards to how the government functions.