A Case Against Coverage-Based Program Spectra

Spectrum-Based Fault Localization (SBFL) is a semi-automated debugging technique that gained popularity in the last decades due to its intuitive approach and relatively simple implementability. Despite this, the performance of practical SBFL techniques in terms of fault localization capability does not reach the threshold that would enable their acceptance by professional programmers. Almost all modern SBFL approaches are based on the code coverage-based spectrum, and on the assumption that a code element covered by failing tests should be treated as suspicious. However, it is easy to see that this is an over-approximation because many code elements may be executed that do not contribute to the test output, hence serving as noise in the process. A possible solution is to use backward dynamic program slices as program spectra computed from the output statement as the criterion, instead of the coverage. There are very few theoretical and practical results about this approach, so in this work we revisit the method and show how much more inferior coverage-based spectra are compared to slice-based spectra, both on theoretical and practical levels. We argue that code coverage-based SBFL is currently in a research pit due to this inherent approximation, and research on slice-based spectra should once more attain a much higher focus.