Making Software Refactorings Safer

Refactorings often require that non-trivial semantic correctness conditions are met. IDEs such as Eclipse’s Java Development Tools rely on simpler, static precondition checks for refactorings. This leads to the phenomenon that a seemingly innocuous refactoring can change the behavior of the program. In this thesis we demonstrate our technique of introducing runtime checks of two particular refactorings for the Java programming language: Extract And Move Method, and Extract Local Variable. These checks can, in combination with unit tests, detect changed behavior and identify the refactoring step that introduced it.