Alannah:
Just in case it's useful, here's a link to the Canadian Language Benchmarks Assessment http://sait.ca/pages/cometosait/internationalstudents/pdf/CLBA1107.pdf
Unlike TOEFL-type tests, this test covers reading, writing, speaking, and listening. I'm far from an expert with this product, but it's one we use at my institution as a benchmark. Just a guess: other countries have something similar. You're right: a documented ability to function in a language is only part of the picture....
Cheers, Chris