On the Disc, there have only been a few recorded duck tests, and never more than one in the same pond. Incidentally, the last duck test in the Ramptops is how the quite stupendously active volcano Mt. Duckmore first got its name, after Esmerelda Weatherwax was once subjected to trial. No-one has really felt the need to try since.

I'm surprised that you, even as a flaired user, would make such a prejudiced inquiry. You imply that witches deserve to be or should be convicted by the duck test. As I have outlined here, what we call "witches" can be either Wicked or Good. There is hardly any need to convict a Good witch.

And of course, the test itself is scientifically flawed. We all know that when witches make contact with water, they instantly begin to dissolve. Thus any test about whether witches can float must be done in oil or pure ethanol, which are heavier and lighter than water respectively. A witch that floats in such a substance will not weigh as a much as a duck which floats in water.