Reminds me of an experiment I read about in which subjects were given a pencil and a piece of paper and asked to strike the paper with the lead as much as they possibly could in a set amount of time. I believe this gave the experimenters a baseline upon which they could judge the participants' ongoing performance. If I remember correctly, they discovered that on days when the subjects' pencil strikes fell well below their average, they were more prone to accidents, injury, other physical mishaps.
Seems to me the exercise the test subjects participated in was a good measure of physical and mental prowess. These 2 facets of our physical state are obviously conjoined and do not commonly act independently of each other.
I lift weights 3 days a week and I keep a log which I write in during the workout. I jot weights, reps, sets, etc. I encounter days in which I add the weight incorrectly, forget to put a plate on the bar, write the wrong figures...a host of mental mistakes which always seem to go hand-in-hand with terrible work outs in which my muscles seem just as sluggish as my brain.
We all have our good days and our bad days. Due to insufficient sleep, illness, stress, distractions, and many other causes we often find ourselves far below our usual levels of mental performance. When we find ourselves in such a state, it's not really worth putting effort in doing many tasks, like programming or long term planning - as quality will suffer a lot.
The problem is - other than observing deterioration of results, I have no idea if I'm in such a state or not. I cannot be sure if it's also true for others, but I had to find out a few tests of what's my mental performance at the moment. Tests that are deeply flawed, so I'd request better if there are any. I also cannot predict my mental state in advance, as my life isn't terribly regular.
The most reliable test I found, and by accident, was fighting bots on a certain Quake 3 map - me vs 10 or so highest difficulty bots. The challenge was to get 50 frags without dying. As the map was huge and full of power ups, it wasn't really that difficult as long as I could maintain full alertness for 10-15 minutes - but if I was tired or distracted, I would invariably fail. This test was unfortunately extremely slow.
Another test would be to go to goproblems, and do a few random problems at proper difficulty level. If I could think right, I would do most of them, if I was tired, I would fail almost 100%. This didn't test alertness, I guess it would be best described as short term memory test, as that's what used for game tree exploration. Unfortunately what's the proper difficulty varies a lot with how much go I played recently, so it needs to be recalibrated.
One more test would be to go to some decent online IQ test like this one. My results on such test would suffer a lot if I was sleepy or tired. The main problem is that such tests cannot repeated too often, or I'd just remember the answers.
So these are three ways to test how well my mind functions at the moment, all testing something different, and all flawed in one way or another.
How do you test yourself?