This paper presents results from a comparative evaluation of five combination strategies. Combination strategies are test case selection methods that combine “interesting ” values of the input parameters of a test subject to form test cases. This research comparatively evaluated five combination strategies; the All Combination strategy (AC), the Each Choice strategy (EC), the Base Choice strategy (BC), Orthogonal Arrays (OA) and the algorithm from the Automatic Efficient Test Generator (AETG). AC satisfies n-wise coverage, EC and BC satisfy 1-wise coverage, and OA and AETG satisfy pair-wise coverage. The All Combinations strategy was used as a “gold standard ” strategy; it subsumes the others but is usually too expensive for practical use. The others were used in an experiment that used five programs seeded with 128 faults. The combination strategies were evaluated with respect to the number of test cases, the number of faults found, failure size, and number of decisions covered. The strategy that requires the least number of tests, Each Choice, found the smallest number of faults. Although the Base Choice strategy requires fewer test cases than Orthogonal Arrays and AETG, it found as many faults. Analysis also shows some properties of the combination strategies that appear significant. The two most important results are that the Each Choice strategy is unpredictable in terms of which faults will be revealed, possibly indicating that faults are found by chance, and that the Base Choice and the pair-wise combination strategies to some extent target different types of faults.

For a given test criterion, the number of test-sets satisfying the criterion may be very large, with varying fault detection effectiveness. In recent work [29], the measure of variation in effectiveness of test criterion was defined as `tolerance'. This paper presents an experimental evaluation of tolerance for control-flow test criteria. The experimental analysis is done by exhaustive test-set generation, wherever possible, for a given criteria which improves on earlier empirical studies that adopted analysis of some test-sets using random selection techniques. Four industrially used control-flow testing criteria, Condition Coverage (CC), Decision Condition Coverage (DCC), Full Predicate Coverage (FPC) and Modified Condition/Decision Coverage (MC/DC) have been analysed against four types of faults. A new test criteria, Reinforced Condition/Decision Coverage (RC/DC) [28], is also analysed and compared. The Boolean specifications considered were taken from a past research paper and also generated randomly. To ensure that it is the test-set property that influences the effectiveness and not the test-set size, the average test-set size was kept same for all the test criteria except RC/DC. A further analysis of variation in average effectiveness with respect to number of conditions in the decision was also undertaken. The empirical results show that the MC/DC criterion is more reliable and stable when compared to the other considered criteria. Though the number of test-cases is large in RC/DC testsets, no significant improvement in effectiveness and tolerance was observed over MC/DC.