T.: Making program refactoring safer

Abstract. Developers rely on compilation, test suite and tools to pre-serve observable behavior during refactorings. However, most of the refac-toring tools do not implement all preconditions that guarantee the refac-toring correctness, since formally identifying them is cost-prohibitive. Therefore, these tools may perform non-behavior-preserving transforma-tions. We present a technique and tool (SafeRefactor) for making pro-gram refactoring safer. It analyzes a transformation and automatically generates a test suite that is suited for detecting behavioral changes. Moreover, we propose a program generator (JDolly) useful for generat-ing inputs for testing refactoring tools. We have evaluated both in two experiments. First, we used SafeRefactor in seven real case study refactorings (from 3 to 100 KLOC). We reason about an original version of JHotDraw (23 KLOC) and its refactored version, and automatically detected a behavioral change. Developers have not identified this prob-lem before. Finally, we have used SafeRefactor and JDolly to test 12 refactorings implemented by Eclipse 3.4.2. As result, we have detected a number of non-behavior-preserving transformations