On the relationship between refactoring actions and bugs: a differentiated replication

Software refactoring aims at improving code quality while preserving the system's external behavior. Although in principle refactoring is a behavior-preserving activity, a study presented by Bavota etal in 2012 reported the proneness of some refactoring actions (eg pull up method) to induce faults. The study was performed by mining refactoring activities and bugs from three systems. Taking profit of the advances made in the mining software repositories field (eg better tools to detect refactoring actions at commit-level granularity), we present a differentiated replication of the work by Bavota etal in which we (i) overcome some of the weaknesses that affect their experimental design, (ii) answer the same research questions of the original study on a much larger dataset (3 vs 103 systems), and (iii) complement the quantitative analysis of the relationship between refactoring and bugs with a qualitative, manual inspection of commits aimed at verifying the extent to which refactoring actions trigger bug-fixing activities. The results of our quantitative analysis confirm the findings of the replicated study, while the qualitative analysis partially demystifies the role played by refactoring actions in the bug introduction.