Earlier quoted context omitted.
I want to test their ability to perform a task - rather than how well they memorized things. Which is not to say that memorization is not important, but it's just one piece of the Puzzle. So when it comes to language tests, rather than having the candidate fill in prepositions into blanks, let's have an actual conversation with them in which they apply their combined skills.
I actually adhere to this philosophy when hiring candidates as well. Rather than having them explain how to reverse binary trees on a whiteboard, I have them sit down and do a mini version of the actual task they will have to do in their job later. And, unsurprisingly, knowing how well they do the actual task is a much better indicator of how well they perform at doing the actual task later.
When I tell people a story about the history of the french revolution or something, I don't have the opportunity to go research it beforehand. I've already done that research, and I've already thought about those events for months or years, which gave me the opportunity to synthesize an insight or opinion I wish to share.
You don't get that if you don't know things in your head.