It's important to remember that there are knots between your reel and the fish.
The best way to test IMO:
Get a fish scale that consists of a gauge and and actual spring set (digital readout is too slow).
Tie your personal knot to a metal ring or something and attach it to the scale.
With the reel on the rod, safety glasses on your face and your eye on the scale, start pulling and tighten the drag until your knot breaks, record this weight.
Repeat the procedure four or five times, then determine the average weight of all the sessions.
Tie back up and set the drag to feed line at 1/3 the average weight it took to break your knot. You will be surprised at how tight this actually is.
Then, leave the drag alone.
I never actually do this, of course, because it's a total PITA. But, it
is the correct way IMO.