If the contest is closed adjudication, then the selections have to be kept secret. The adjudicators would have to be informed as to what the next piece was, but not which band.
That said, it seems to me that keeping this a complete secret in the situation described might be a little difficult. So if the secret gets out for one band, wouldn't it be more fair if all of the selections were made known in advance? That way, no one could claim foul based on their secret getting out ahead. The adjudication could still be "closed" unless one of the three tests was chosen by only one group, assuming that the judges don't know the draw. Of course, the choice to announce or not announce selections is up to the organizers of the contest, and we should respect the rules.
I'm also curious about how the contest will be conducted. Will there be a draw for each test piece, with all of the bands doing the same piece playing in sequence, and then going on to those doing the next piece? Or will there be one draw for everybody, with the pieces coming in a random fashion? It seems to me that randomness might make for some confusion in the judging booths.