The Impact of Coverage on Bug Density in a Large Industrial Software Project

Measuring quality of test suites is one of the major challenges of software testing. Code coverage identifies tested and untested parts of code and is frequently used to approximate test suite quality. Multiple previous studies have investigated the relationship between coverage ratio and test suite quality, without a clear consent in the results. In this work we study whether covered code contains a smaller number of future bugs than uncovered code (assuming appropriate scaling). If this correlation holds and bug density is lower in covered code, coverage can be regarded as a meaningful metric to estimate the adequacy of testing. To this end we analyse 16000 internal bug reports and bug-fixes of SAP HANA, a large industrial software project. We found that the above-mentioned relationship indeed holds, and is statistically significant. Contrary to most previous works our study uses real bugs and real bug-fixes. Furthermore, our data is derived from a complex and large industrial project.