I reread rrc's comment, which seems could be interpreted as both ways; either to advocate requirement of positive identification to vote, or to require voters to take an exam to be licensed as a voter, which is what I believe what was meant.

regardless, literacy tests were done before, see http://en.wikipedia.org/wiki/Literacy_test and http://en.wikipedia.org/wiki/Jim_Crow_laws for a background of our (shameful) past.