Software testing for dependability assessment

Software testing can be aimed at two different goals: removing faults and evaluating dependability. Testing methods described in textbooks having the word "testing" in their title or more commonly used in the industry are mostly intended to accomplish the first goal: revealing failures, so that the faults that caused them can be located and removed. However, the final goal of a software validation process should be to achieve an objective measure of the confidence that can be put on the software being developed. For this purpose, conventional reliability theory has been applied to software engineering and nowadays several reliability growth models can be used to accurately predict the future reliability of a program based on the failures observed during testing. Paradoxically, the most difficult situation is that of a software product that does not fail during testing, as is normally the case for safety-critical applications. In fact, quantification of ultrareliability is impossible at the current state of the art and is the subject of active research. It has been recently suggested that measures of software testability could be used to predict higher dependability than black-box testing alone could do.