A number of structural coverage criteria have been proposed to measure the adequacy of testing efforts. In the avionics and other critical systems domains, test suites satisfying structural coverage criteria are mandated by standards. With the advent of powerful automated test generation tools, it is tempting to simply generate test inputs to satisfy these structural coverage criteria. However, while techniques to produce coverage-providing tests are well established, the effectiveness of such approaches in terms of fault detection ability has not been adequately studied. In this work, we evaluate the effectiveness of test suites generated to satisfy four coverage criteria through counterexample-based test generation and a random generation approach-where tests are randomly generated until coverage is achieved-contrasted against purely random test suites of equal size. Our results yield three key conclusions. First, coverage criteria satisfaction alone can be a poor indication of fault finding effectiveness, with inconsistent results between the seven case examples (and random test suites of equal size often providing similar-or even higher-levels of fault finding). Second, the use of structural coverage as a supplement-rather than a target-for test generation can have a positive impact, with random test suites reduced to a coverage-providing subset detecting up to 13.5% more faults than test suites generated specifically to achieve coverage. Finally, Observable MC/DC, a criterion designed to account for program structure and the selection of the test oracle, can-in part-address the failings of traditional structural coverage criteria, allowing for the generation of test suites achieving higher levels of fault detection than random test suites of equal size. These observations point to risks inherent in the increase in test automation in critical systems, and the need for more research in how coverage criteria, test generation approaches, the test oracle used, and system structure jointly influence test effectiveness.

Abstract. In the avionics domain, the use of structural coverage criteria is legally required in determining test suite adequacy. With the success of automated test generation tools, it is tempting to use these criteria as the basis for test generation. To more firmly establish the effectiveness of such approaches, we have generated and evaluated test suites to satisfy two coverage criteria using counterexample-based test generation and a random generation approach, contrasted against purely random test suites of equal size.Our results yield two key conclusions. First, coverage criteria satisfaction alone is a poor indication of test suite effectiveness. Second, the use of structural coverage as a supplement-not a target-for test generation can have a positive impact. These observations points to the dangers inherent in the increase in test automation in critical systems and the need for more research in how coverage criteria, generation approach, and system structure jointly influence test effectiveness.

Abstract-In many critical systems domains, test suite adequacy is currently measured using structural coverage metrics over the source code. Of particular interest is the modified condition/decision coverage (MC/DC) criterion required for, e.g., critical avionics systems. In previous investigations we have found that the efficacy of such test suites is highly dependent on the structure of the program under test and the choice of variables monitored by the oracle. MC/DC adequate tests would frequently exercise faulty code, but the effects of the faults would not propagate to the monitored oracle variables.In this report, we combine the MC/DC coverage metric with a notion of observability that helps ensure that the result of a fault encountered when covering a structural obligation propagates to a monitored variable; we term this new coverage criterion Observable MC/DC (OMC/DC). We hypothesize this path requirement will make structural coverage metrics 1.) more effective at revealing faults, 2.) more robust to changes in program structure, and 3.) more robust to the choice of variables monitored. We assess the efficacy and sensitivity to program structure of OMC/DC as compared to masking MC/DC using four subsystems from the civil avionics domain and the control logic of a microwave. We have found that test suites satisfying OMC/DC are significantly more effective than test suites satisfying MC/DC, revealing up to 88% more faults, and are less sensitive to program structure and the choice of monitored variables.

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