Generating Effective Test Suites by Combining Coverage Criteria

A number of criteria have been proposed to judge test suite adequacy. While search-based test generation has improved greatly at criteria coverage, the produced suites are still often ineffective at detecting faults. Efficacy may be limited by the single-minded application of one criterion at a time when generating suites—a sharp contrast to human testers, who simultaneously explore multiple testing strategies. We hypothesize that automated generation can be improved by selecting and simultaneously exploring multiple criteria. To address this hypothesis, we have generated multi-criteria test suites, measuring efficacy against the Defects4J fault database. We have found that multi-criteria suites can be up to 31.15% more effective at detecting complex, real-world faults than suites generated to satisfy a single criterion and 70.17% more effective than the default combination of all eight criteria. Given a fixed search budget, we recommend pairing a criterion focused on structural exploration—such as Branch Coverage—with targeted supplemental strategies aimed at the type of faults expected from the system under test. Our findings offer lessons to consider when selecting such combinations.