@Curmudgeon,
Freeman, I'd be in favor of such a test, but then I'd be even more in favor of a system of citizenship as proposed by Heinlein in the book
Starship Troopers, a far better book than the movie, who's only resemblance to the book was the title.
But both of us know that any such proposal (yours or mine) would be quickly stricken down by the courts as unconstitutional. There have been many attempts in history to limit the voting population, and most of these were actually little disguised attempts to keep various groups (black, women, and others) from voting. Because of this historical record, any future attempts to ensure an informed voting populace will be doomed before it ever even gets on paper.