A few days before a cholesterol test I stop drinking liquor, stop eating red meat, exercise, and eat brown rice and carrots. After the test I go to a bar, have tomato pies with the works, accompanied by buckets of beer. I know someone in Weight Watchers and she runs out after being weighed on the scale and has cheese steaks, fries and gallons of Pinot Grigiot. Before a civil service test we cram for the exam, take the test and forget everything the next day.
That's why all tests should be random and unexpected. They should measure us as we really are, not as we pretend to be. As unexpected as a fire alarm on a cold morning, and as welcome.
2AM on a Sunday morning, the fire truck drives up to the house. The tester knocks on the door. The would-be fireman appears in his underwear, full of beer. He then goes up on the ladders and demonstrates his prowess with a hose. Tuesday night at 9PM someone from LabCorp shows up at your door step and takes a blood sample. He measures you as you really live.
Random testing brings accurate results. Like the surprise quizzes in high school that brought C's to everybody, including the Honor Club crowd.