"Poka-yoke devices fall into two major categories: prevention and detection. A prevention device engineers the process so that it is impossible to make a mistake at all. A classic example of a prevention device is the design of a 3.5 inch computer diskette.The diskette is carefully engineered to be slightly asymmetrical so that it will not fit into the disk drive in any orientation other than the correct one. Prevention devices remove the need to correct a mistake, since the user cannot make the mistake in the first place. A detection device signals the user when a mistake has been made, so that the user can quickly correct the problem. The small dish used at the Yamada Electric plant was a detection device; it alerted the worker when a spring had been forgotten. Detection devices typically warn the user of a problem, but they do not enforce the correction. ... [in software tesging] Unit testing and "smoke testing" [7] come closer to the notion of poka-yoke, in that they are located close to the source of the potential mistakes and the quick feedback they provide can keep mistakes from moving further along in the process."
