On the impact of timeouts and JVM crashes in Pitest

Mutation analysis is a strong, well studied, faultbased testing criterion that has been shown to lead to strong test suites. Still, when using mutation analysis to compare test suites, previous work has shown that its results can be skewed because of redundant mutants. This problem is avoided by using minimal mutants, a set of representative mutants that is computed from a full matrix of all test results against all mutants. Pitest is a state of the art mutation analysis tool for Java and the JVM that can produce the matrix needed to compute minimal mutants. When a mutant leads to a JVM crash, because of a timeout or a memory error for example, Pitest does not record the full information about a mutant, leading to an incomplete matrix. In this work, we update Pitest in order to obtain the complete matrix, and make our updated version available. We then study the impact of the incomplete matrix on both minimal mutant computation and test selection, using both open source projects and developer-made test suites as well as a set of well tested methods. Finally, using the data collected, we see whether particular characteristics of a mutant or a test can help predict whether a test run against a mutant will lead to a JVM crash. Our experiments show that the missing information in Pitest's matrix has little impact on the computed set of minimal mutants and the tests it selects. We also find no indication that particular mutation operator or test systematically leads to JVM crashes.