Perhaps not a forced swim test, but having a human swim in place (or tread water) for as long as they can. In a swimming pool, with people around to rescue them

Perhaps not a forced swim test, but having a human swim in place (or tread water) for as long as they can. In a swimming pool, with people around to rescue them if they stop swimming and start drowning, and being removed as soon as they give up by ... I don't know, going over and grabbing the edge of the pool? Or making some unambiguous hand gesture, or yelling a safe word, or whatever. I'm not entirely sure how valid the results from this would be, but there's also controversy over forced swim tests with rats and mice, so it would probably be just as accurate.