Decision making and mental fatigue

Scientific American published an article about how decision making affects the brain. Apparently deciding not to overeat taxes the same part of your brain (the "executive function") that you use to make important decisions.

"Imagine, for a moment, that you are facing a very difficult decision about which of two job offers to accept. One position offers good pay and job security, but is pretty mundane, whereas the other job is really interesting and offers reasonable pay, but has questionable job security. Clearly you can go about resolving this dilemma in many ways. Few people, however, would say that your decision should be affected or influenced by whether or not you resisted the urge to eat cookies prior to contemplating the job offers. A decade of psychology research suggests otherwise. Unrelated activities that tax the executive function have important lingering effects, and may disrupt your ability to make such an important decision. In other words, you might choose the wrong job because you didn't eat a cookie."

Research even suggests that just doing things that require making choices as simple as shopping or marking preferences on courses deplete your executive function and make later decision making harder.

The article doesn't address whether you can develop your capacity for executive function, but my experience suggests that this is the case. It also makes me wonder - are there tests that can show a persons executive function capacity? The ability to make important decisions when fatigued is important for many different jobs - a test of this kind could be useful in hiring or job placement. Also, the ability to find a baseline and subsequent improvements would be important if you wanted to improve your executive function.