Adding any kind of discrimination to an election process (which is a right and has to be open to all) is not a good idea, since it opens the way to all sort of abuse (see the comment on literacy tests), in the way it is evaluated. I don't see a way for such a test to exist, without any bias that could create discrimination.

And even if people are informed, it does not mean they would chose according to that knowledge, since I think a lot of people vote not according to their brain, but follow their emotions or the expectations of their social group.