It is not the voter that needs to be to be tested before being allowed to vote, it is every citizens right to participate in electing our government. It is the candidates that need a test before being allowed to hold office. The number of Congressmen that exhibit an ignorance of the Constitution, the intent of the Bill of Rights, Civil Rights, exhibit ignorance of the subject of the committee they are sitting on (such as science), is appalling.
A test for potential candidates covering American History, the Constitution, US Government, and at least High School level Science may be a good idea.