Carving differential unit test cases from system test cases

Unit test cases are focused and efficient. System tests are effective at exercising complex usage patterns. Differential unit tests (DUT) are a hybrid of unit and system tests. They are generated by carving the system components, while executing a system test case, that in- fluence the behavior of the target unit, and then re-assembling those components so that the unit can be exercised as it was by the sys- tem test. We conjecture that DUTs retain some of the advantages of unit tests, can be automatically and inexpensively generated, and have the potential for revealing faults related to intricate system ex- ecutions. In this paper we present a framework for automatically carving and replaying DUTs that accounts for a wide-variety of strategies, we implement an instance of the framework with sev- eral techniques to mitigate test cost and enhance flexibility, and we empirically assess the efficacy of carving and replaying DUTs.