Identifying Test Refactoring Candidates with Assertion Fingerprints

Test cases constitute around 30% of the codebase of a number of large software systems. Poor design of test suites hinders test comprehension and maintenance. Developers often copy-paste existing tests and reproduce both boilerplate and essential environment setup code as well as assertions. Test case refactoring would be valuable for developers aiming to control technical debt arising due to copy-pasted test cases. In the context of test code, identifying candidates for refactoring requires tedious manual effort. In this work, we specifically tailor static analysis techniques for test analysis. We present a novel technique, assertion fingerprints, for finding similar test cases based on the set of assertion calls in test methods. Assertion fingerprints encode the control flow around the ordered set of assertions in methods. We have implemented similar test case detection using assertion fingerprints and applied it to 10 test suites for open-source Java programs. We provide an empirical study and a qualitative analysis of our results. Assertion fingerprints enable the discovery of tests that exhibit strong structural similarities and are amenable to refactoring. Our technique delivers an overall 75% true positive rate on our benchmarks and reports that 40% of the benchmark test methods are potentially refactorable.