I think it may be unreasonable to assume that the requirement passed to the developer was clear and correct. The unit test is itself predicated on the belief that the requirement is clear and correct and, in my experience, this very often is not the case.<p>IMHO, many administrators or managers lack a strong math background and may find themselves writing requirements that involved fairly complicated arithmetic in narrative form, thus introducing considerable &quot;gray error&quot; and potential error. I&#x27;ve seen it many times in my own work.