I don't know about other languages, but the French government actually does have tests of French fluency (DELF/DALF exam), which test you in a range of ways (oral comprehension - usually a radio emission, written comprehension - usually a news article, writing on a choice of subjects and speaking - presenting a view on a subject and then debating), at a variety of levels. I took one of these tests (I'm fluent, yay!), and it certainly was testing. But it seemed fair and appropriate, also seemed to correlate with my experiences speaking to French people in France.