A multidimensional empirical study on refactoring activity

In this paper we present an empirical study on the refactoring activity in three well-known projects. We have studied five research questions that explore the different types of refactorings applied to different types of sources, the individual contribution of team members on refactoring activities, the alignment of refactoring activity with release dates and testing periods, and the motivation behind the applied refactorings. The studied projects have a history of 12, 7, and 6 years, respectively. We have found that there is very little variation in the types of refactorings applied on test code, since the majority of the refactorings focus on the reorganization and renaming of classes. Additionally, we have identified that the refactoring decision making and application is often performed by individual refactoring "managers". We have found a strong alignment between refactoring activity and release dates. Moreover, we found that the development teams apply a considerable amount of refactorings during testing periods. Finally, we have also found that in addition to code smell resolution the main drivers for applying refactorings are the introduction of extension points, and the resolution of backward compatibility issues.