Yes, there's an experimental test -- as in, testing to see if salt is salt. But I dont think there's a formal test... as soon as you specify it, you've eliminated the need for intelligence. Intelligence is in that process of specification.
In otherwords, we should be able to ask the machine "what do you think of woody allen's films?" and rather than just taking any answer.. we need an empirical test to see if the machine has actually understood the question. Not a formal test.
There is no doubt a sequence of replies which will convince a person that the machine has understood the question: just record them, and play them back.
We're not interested in the replies. We're interested in whether the machine is actually thinking about the world. Is it evaluating the films? What are its views? What if I show it a bad film and say it wasnt by woody allen? What then?
There's something wrong in seeing this as a formal, rather than experimental, process. For any given machine we will need specific hypothesis tests as to its "intelligence", and we will need to treat it like any other empirical system.