The subject of this book is testing. The origin of testing lies within a magical epiphany. Almost four thousand years ago, an anonymous functionary was focused on a task set before him by the emperor of China. He needed a procedure to choose wisely from among all applicants for government positions. Perhaps, utilizing a model made famous by Newton three millennia later, he was lying under a tree when the fundamental principle of testing struck him:

Testing is an ingenious solution to a practical problem. In an ideal world, before choosing among candidates for some position, we would like to know how they would perform in that position. Obviously, if we could place each of them in the position for a long enough period of time we would have direct evidence, but such a solution is usually not a practical possibility. But, even in a situation in which we had, say a year of trial, we would still not know for sure how they would perform after two years, or three, or more. In this instance, however, we would be pretty convinced of the validity of the task utilized to make the decision – it is, after all, the same job. But if the tasks on the job vary, the one-year trial period may not be long enough.