Is This Really a Refactoring? Automated Equivalence Checking for Erlang Projects

We present an automated approach to checking whether a change to a repository is a refactoring, that is, it makes no change to the behaviour of the system. This is implemented in the EquivcheckEr tool, which detects the places in which the code has changed, and compares the old and new versions of all functions that are affected by the change, applying the functions to randomly generated inputs. Our tool works for projects written in Erlang, and so needs to deal with effectful as well as pure functions. We aim only to report inequivalence when we have concrete evidence to that effect, avoiding any “false positive” counterexamples.