You guys were spot on with the gyms in Ultra Sun/Moon, but it'll act differently. Before you take on a trial, you have to battle the trial captain, to test your strength. They don't have the typical trainer battle theme, though. You'll hear that in a trailer.

The Trial Captains you have to face are Illima, Lana, Kiawe, Mallow, a new rock captain, Sophocles, Acerola and Mina.