I was imagining some sort of series of tasks to be performed by left and by right hand, scored for accuracy and timed for speed, with some sort of statistical analysis to determine if you are more left or right handed. The sort of thing that in my mind I imagine sensible people running children through before starting to teach them to write, so you could start them with the better hand. Because how would you know unless you do some sort of careful test?
Anyway, I went looking and found the Edinburgh Handedness Inventory, which is just an amazingly pathetic inventory. Try this slightly expanded version. For one thing, it starts off with things obviously influenced by the do-this-right-handed world around you, like the overwhelming majority of scissors not really working left-handed. A handedness inventory that asks if you've gotten so fed up with trying to use right-handed scissors that you went and obtained special left-handed scissors isn't going to tell us anything we didn't already know. We don't need a test for the really obvious cases.
The other thing is, wow, those are some "handed" activities? Using a spoon? Opening a box? People actually do those consistently left or right handed? Brush or comb? Surely you tend to use the left hand for the left side of the head, right hand for the right side? Unlocking a door? Wouldn't that just depend on which side of the door the lock is on, and from with side you approach the door, and which hand you happen to have the key in when you get there? These seem to me like an entirely different order of tasks from handwriting, seemingly far below the threshold of caring which hand you use.
Eye dominance tests, those are also a mystery to me, setting me up to see a perfectly matched symmetrical pair of images and implying vaguely that I should be seeing something different. As far as I have seen, eye dominance tests are scored on a 100:0 or 0:100 or else "no dominant eye" basis, apparently no one has been interested in taking the time to develope a test carefully crafted enough to score you as a 48:52 or whatever.
I'm also left thinking there is some sort of metaphor for gender in this, that there are exactly two and everyone is obviously one or the other. (I'm starting to wonder if maybe there are some aspects to gender that are as mysterious to me as handedness. I suspect there may be.)