If you know something “for academic purposes” you are able to compose a coherent prose paragraph about it. We can even specificy ideal conditions for this “moment of composition”: give yourself five minutes at the end of one day to decide what to say, 27 minutes at the beginning of the next to write it down, and no time to learn anything in the meantime. If you can write under these conditions, you know what you’re talking about. Now consider composing five paragraphs in a row this way, again having decided the day before on a larger thesis. There is nothing unreasonable about this exercise as a test of your knowledge and it is, in fact, a great way to get two or three pages of a paper or book written on any given morning. If we replace the decision the day before with a prompt issued on the day, it is also a perfectly fair test of what your students have learned in your class. They can train for it every morning, one paragraph at a time. If they can do it, so can you.