FLUCCS: using code and change metrics to improve fault localization

Fault localization aims to support the debugging activities of human developers by highlighting the program elements that are suspected to be responsible for the observed failure. Spectrum Based Fault Localization (SBFL), an existing localization technique that only relies on the coverage and pass/fail results of executed test cases, has been widely studied but also criticized for the lack of precision and limited effort reduction. To overcome restrictions of techniques based purely on coverage, we extend SBFL with code and change metrics that have been studied in the context of defect prediction, such as size, age and code churn. Using suspiciousness values from existing SBFL formulas and these source code metrics as features, we apply two learn-to-rank techniques, Genetic Programming (GP) and linear rank Support Vector Machines (SVMs). We evaluate our approach with a ten-fold cross validation of method level fault localization, using 210 real world faults from the Defects4J repository. GP with additional source code metrics ranks the faulty method at the top for 106 faults, and within the top five for 173 faults. This is a significant improvement over the state-of-the-art SBFL formulas, the best of which can rank 49 and 127 faults at the top and within the top five, respectively.