It's a bad idea. For various reasons. Who will be writing the test questions? Will it really be fair? I know people talk about "discrimination against minorities" but it could be discriminate against anyone. If extreme Liberal Democrats write the brunt of the material then it tips against people who are Conservative. And if the opposite happens because of extreme Conservative Republicans, then liberally minded folks get screwed.
Now I do think that voter I.Ds need to happen, because there are many MANY things that the government requires people to have to purchase certain items and to perform a plethora of functions in society. I actually know people from home (US) that got bored and voted four different times in different cities in my state, and they were able to because there is no system in place to combat that. And there are people who will still call it racist and discriminatory, but I've only seen this to be propaganda or shrt sighted at best. It takes maybe $20 to get a form of ID, whether it's a Driver's Liscense or what. And if you have to have an ID to do less important things like drive, buy alcohol, buy a gun, open a bank account, apply for food stamps, welfare, and social security checks, get on an airplane, GET MARRIED, ADOPT A PET, and to hold a rally or protest, then voting (the most important function of our citizenry) should be required for that as well.