then there's this, from wikipedia:
The "right to vote" is explicitly stated in the US Constitution in the above referenced amendments but only in reference to the fact that the franchise cannot be denied or abridged based solely on the aforementioned qualifications. In other words, the "right to vote" is perhaps better understood, in layman's terms, as only prohibiting certain forms of legal discrimination in establishing qualifications for suffrage.
States may deny the "right to vote" for other reasons.For example, many states require eligible citizens to register to vote a set number of days prior to the election in order to vote. More controversial restrictions include those laws that prohibit convicted felons from voting or, as seen in Bush v. Gore, disputes as to what rules should apply in counting or recounting ballots [2]
A state may choose to fill an office by means other than an election. For example, upon death or resignation of a legislator, the state may allow the affiliated political party to choose a replacement to hold office until the next scheduled election. Such an appointment is often affirmed by the governor.[3]
http://en.wikipedia.org/wiki/Voting_..._United_States
its only the reasons stated in the amendments to the constitution that bar specific discriminations. religion, age, race. nothin g in there about id. states are the ones who set rules other than what is included in the amendments. so, yes, actually, a state could actually test people. it's not something explicitly banned.