An Empirical Study of Dormant Bugs

Over the past decade, several research efforts have studied the quality of software systems by looking at post-release bugs. However, these studies do not account for bugs that remain dormant (i.e., introduced in a version of the software system, but are not found until much later) for years and across many versions. Such dormant bugs skew our under-standing of the software quality. In this paper we study dormant bugs against non-dormant bugs using data from 20 different open-source Apache foun-dation software systems. We find that 33 % of the bugs intro-duced in a version are not reported till much later (i.e., they are reported in future versions as dormant bugs). Moreover, we find that 18.9 % of the reported bugs in a version are not even introduced in that version (i.e., they are dormant bugs from prior versions). In short, the use of reported bugs to judge the quality of a specific version might be misleading. Exploring the fix process for dormant bugs, we find that they are fixed faster (median fix time of 5 days) than non-dormant bugs (median fix time of 8 days), and are fixed by more experienced developers (median commit counts of de-velopers who fix dormant bug is 169 % higher). Our results highlight that dormant bugs are different from non-dormant bugs in many perspectives and that future research in soft-ware quality should carefully study and consider dormant bugs