Testing Complex Logic

Choosing effective tests for complex logical expressions can be difficult. This paper describes a black box strategy for choosing such tests. The strategy is shown to be a natural generalization of current methods for choosing tests for simpler expressions. The strategy chooses combinations that are not only effective at revealing implementation defects but, perhaps more important, are effective at helping detect defects in the requirements themselves. In addition, if there are dependencies between variables in the required logic, a variant of the strategy excludes those truth-value combinations that are "impossible" because of the dependencies. It extends the required expression to include dependency information and then derives tests from this extension. This strategy is the only test selection method that smoothly incorporates dependency information. It also permits the dependency information itself to be partially validated through analysis of the "impossible" cases developed by the basic strategy, but excluded by the variant.

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