Retrofitting Unit Tests for Parameterized Unit Testing Suresh Thummalapenta 1 , Madhuri R. Marri 1 , Tao Xie 1 , Nikolai Tillmann 2 , and Jonathan de Halleux 2 1 Department of Computer Science, North Carolina State University, Raleigh, USA {sthumma,mrmarri,txie}@ncsu.edu 2 Microsoft Research, One Microsoft Way, Redmond, USA {nikolait, jhalleux}@microsoft.com Abstract. Recent advances in software testing introduced parameterized unit tests (PUT), which accept parameters, unlike conventional unit tests (CUT), which do not accept parameters. PUTs are more beneficial than CUTs with re- gards to fault-detection capability, since PUTs help describe the behaviors of methods under test for all test arguments. In general, existing applications often include manually written CUTs. With the existence of these CUTs, natural ques- tions that arise are whether these CUTs can be retrofitted as PUTs to leverage the benefits of PUTs, and what are the cost and benefits involved in retrofitting CUTs as PUTs. To address these questions, in this paper, we conduct an empirical study to investigate whether existing CUTs can be retrofitted as PUTs with feasi- ble effort and achieve the benefits of PUTs in terms of additional fault-detection capability and code coverage. We also propose a methodology, called test gen- eralization, that helps in systematically retrofitting existing CUTs as PUTs. Our results on three real-world open-source applications (≈ 4.6 KLOC) show that the retrofitted PUTs detect 19 new defects that are not detected by existing CUTs, and also increase branch coverage by 4% on average (with maximum increase of 52% for one class under test and 10% for one application under analysis) with feasible effort. 1 1 Introduction Unit tests are widely adopted in software industry for ensuring high quality of production code. Unit testing helps detect defects at an early stage, reducing the effort required in fixing those defects. Recent advances in unit testing introduced parameterized unit tests (PUT) [23], which accept parameters, unlike conventional unit tests (CUT), which do not accept parameters. Existing state-of-the-art test-generation approaches such as Dynamic Symbolic Execution (DSE) [15, 10, 20, 22] can be used in combination with PUTs to automatically generate CUTs by instantiating the parameters. In particular, DSE systematically explores the code under test exercised by a PUT and generates CUTs that achieve high structural coverage such as branch coverage of the code under test. Section 2 presents more details on how CUTs can be generated from PUTs via DSE. In general, PUTs are more beneficial than CUTs. The primary reason is that PUTs help describe the behaviors of methods under test for all test arguments. With PUTs, test data can be automatically generated using DSE-based approaches, thereby helping 1 The first and second authors have made equal contributions. D. Giannakopoulou and F. Orejas (Eds.): FASE 2011, LNCS 6603, pp. 294–309, 2011. c  Springer-Verlag Berlin Heidelberg 2011