CyPhyTest: Cyber Physical Interaction Aware Test Case Generation to Identify Operational Changes

The operational characteristics of a cyber-physical system (CPS) may deviate from the certified system due to intended (in case of cheating) or unintended (wear and tear) reasons. A modification suggested to the original certification process requires the CPS operation to satisfy a contract that allows for testing the CPS deployment with variations of the standard test case. Doping test is then utilized to attempt to derive a test case that satisfies the input contract but violates the output regulations. Although a significant step towards verifying oper-ational characteristics of CPS, the search mechanism in doping test is only limited to the input space of the cyber subsystem and ignores the characteristics of the dynamic interactions in a CPS. This results in test cases that are practically unfeasible for the CPS to replicate. This paper proposes CyPhyTest that makes test case search aware of the multidimensional interactions between the cyber and physical subsystems and addresses practical dynamical system problems like Zeno behavior and dynamical model divergence. CyPhyTest, dynamically modulates the input search space by predicting and limiting input variations that can potentially cause divergence or Zeno behavior. We show the usage of the CyPhyTest framework in identifying a contract violating test case for an automobile emission control system equipped with a Volkswagen-like cheating device.