An empirical study on the fault-proneness of clone migration in clone genealogies

Copy and paste activities create clone groups in software systems. The evolution of a clone group across the history of a software system is termed as clone genealogy. During the evolution of a clone group, developers may change the location of the code fragments in the clone group. The type of the clone group may also change (e.g., from Type-1 to Type-2). These two phenomena have been referred to as clone migration and clone mutation respectively. Previous studies have found that clone migration occur frequently in software systems, and suggested that clone migration can induce faults in a software system. In this paper, we examine how clone migration phenomena affect the risk for faults in clone segments, clone groups, and clone genealogies from three long-lived software systems JBoss, APACHE-ANT, and ARGOUML. Results show that: (1) migrated clone segments, clone groups, and clone genealogies are not equally fault-prone; (2) when a clone mutation occurs during a clone migration, the risk for faults in the migrated clone is increased; (3) migrating a clone that was not changed for a longer period of time is risky.