Exhaustive testing is the name given to a test approach, which uses all possible combinations of test inputs to verify a software system. This approach is only applicable to tiny software systems or components with a close finite number of possible of operations and allowed data. In the majority of software systems, it is not feasible to verify every possible permutation and input combination, and therefore exhaustive testing is just a theoretical approach.
For that reason, it is said that the absence of defects in a software system cannot be proved. This was stated by the computer science pioneer Edsger W. Dijkstra (see quote at beginning of this chapter). Thus, testing is, at best, sampling, and it must be carried out in any software project to reduce the risk of system failures (see chapter 1, Retrospective On Software Quality And Java Testing...