the trouble with questions like these are the convenient-outs. if you were to ask a devout religionist why the earthquake happened, the response would be "because the lord works in mysterious ways". or, like you mentioned, "it's a test of faith".
i must admit that, in terms of god, i am a bit biased. i feel that the bible (the only true "evidence" of any god) could have been written by a human being, and that there is absolutely nothing that proves otherwise.
haiti is just one example. did 9/11 happen because there isn't a god? what about pearl harbor? the holocaust? which brings up another question: if there IS a god, which one is the real one? the tragedy in haiti might prove that haiti's god is false, but mohammed is true. 9/11 might prove that mohammed is false, but the christian god is true.
so frankly, i don't believe that haiti proves anything about god. it's either something that happened naturally (supporting the theory of evolution), or it's something that god wanted to happen (but we're not sure which god).