Studying Co-evolution of Production and Test Code Using Association Rule Mining

Long version of the short paper accepted for publication in the proceedings of the 6th International Working Conference on Mining Software Repositories (MSR 2009). Unit tests are generally acknowledged as an important aid to produce high quality code, as they provide quick feedback to developers on the correctness of their code. In order to achieve high quality, well-maintained tests are needed. Ideally, tests co-evolve with the production code to test changes as soon as possible. In this paper, we explore an approach to determine whether production and test code co-evolve synchronously. Our approach is based on applying association rule mining to the change history of product and test code classes. Based on these co-evolution rules, we introduce a number of measures to assess the co-evolution of product and test code classes. Through two case studies, one with an open source and another one with an industrial software system, we show that association rule mining and our set of measures allows one to assess the co-evolution of product and test code in a software project and, moreover, to uncover the distribution of programmer effort over pure coding, pure testing, or a more test-driven-like practice.