On test case reduction for testing safety properties of manufacturing systems

Artikel i vetenskaplig tidskrift, 2022

This paper presents an approach to reduce the number of test cases, and hence testing time for the safe input-output conformance simulation relation (safe-IOCOS). The safe-IOCOS relation requires the implementation to be trace equivalent with respect to the specification only for traces composed of safety behaviors, which makes safe-IOCOS a suitable relation to test safety properties in practical settings. However, in typical manufacturing systems, multiple safety behaviors are typically associated with each nominal operation in the implementation. Thus, if safe-IOCOS is used industrially then testing for safety related faults becomes time consuming as the traces composed of same safety behaviors gets tested multiple times. This is possible either if the target states reached after the execution of traces have the same past behavior or the same future behavior. To remedy this, two reduction methods are proposed in this paper, subset construction and bisimulation equivalence. Both reduction methods preserve the traces of the system. Using both subset construction and bisimulation, a given specification can be maximally reduced and then used to implement the manufacturing system. The implementation based on a maximally reduced bisimilar specification allows the test engineer to omit test cases if the same safety behavior has already been tested. Furthermore, faults related to missing safety behaviors that are associated with multiple traces can be uncovered more efficiently compared to if the non-reduced specification is used for testing. To summarize, testing is a laborious problem, which can benefit from methods that enable reduction in testing time and makes the testing procedure efficient in terms of uncovering errors.