I've heard two different tests described for Smith and Wessons.
1) In both single and double action, slowly pull the trigger or hammer back, while the cylinder drags on your thumb. If it locks up prior to or during hammer time, it is in time.
2) pull the trigger or cock the hammer with force. If it is locked, it is in time.
I go with number 1, which is more conservative. I figure my main application for the revolver I had that failed test 1 was deer hunting, where I would cock the revolver really slowly to not make noise. This is all based on a massive purse swinging thread from the Smith and Wesson forums 15 years ago.