If you can't tell the difference between a machine and a human being you should have your eyes tested

If you can't tell the difference between a machine and a human being you must concede that the machine must be capable of thought

If you can't tell the difference between a machine and a human being you must concede that human beings do not have freewill

If you can't tell the difference between a machine and a human being so long as you are restricted to communicating via computer screens you must conclude that the essence of being human is having a body.

Which is the best formulation of the Turing test?

Turing thought of his test as a test for whether a machine could be said to be capable of thought, so (1) is not a correct statement of it. (2) is subtly wrong - it's thinking it purports to prove, not freewill (I may not have made this sufficiently memorable).

(4) is tetchy.

(3) seems right to me.