Generating Succinct Test Cases Using Don't Care Analysis

We study the problem of reducing test cases generated by bit vector based symbolic execution test generators. In particular, we first consider a guileless test case generation approach that generates assignment statements for each symbolic scalars, array and structure elements and object fields. We show that test cases generated by this approach can be significantly verbose. We then propose a method for making the generated test cases more succinct using a novel analysis entitled don't care analysis. Don't care analysis identifies assignment statements that can be safely removed from the test cases without affecting the overall code coverage. Our algorithm is based on binary and delta-debugging search. Because it exploits the knowledge of the internal SAT solver, it is effective and efficient in practice. To our knowledge, this is the first fully automatic approach that reduces the sizes of test cases generated using symbolic execution. We implement our test case reduction technique for the KLEE test generation tool and evaluate on 295 programs and functions. Our results are encouraging: in average, the reduced test cases are 50 times smaller than the test cases generated by the guileless test case generator. In addition, since our don't care analysis is tightly integrated into the test case generation tool, its overhead to the overall test generation process is negligible.