Bug prevention

Testing and test design, as parts of quality assurance, should also focus on bug prevention. To the extent that testing and test design do not prevent bugs, they should be able to discover symptoms caused by bugs. Finally, tests should provide clear diagnoses so that bugs can be easily corrected. Bug prevention is testing's first goal. A prevented bug is better than a detected and corrected bug because if the bug is prevented, there's no code to correct. Moreover, no retesting is needed to confirm that the correction was valid, no one is embarrassed, no memory is consumed, and prevented bugs can't wreck a schedule. More than the act of testing, the act of designing tests is one of the best bug preventers known. The thinking that must be done to create a useful test can discover and eliminate bugs before they are coded—indeed, test-design thinking can discover and eliminate bugs at every stage in the creation of software, from conception to specification, to design, coding, and the rest. The ideal test activity would be so successful at bug prevention that actual testing would be unnecessary because all bugs would have been found and fixed during test design.