Model-based testing is a compelling method for the integration testing of microservices. However, when testing with a large number of services, state space explosions are a common problem. It is especially a problem in model-based testing since the input-output conformance (ioco) relation is not compositional. We developed a novel and theoretically grounded testing method called model-based mocking (MBM) to test microservice systems by mocking the underlying services of a SUT during testing. MBM is sufficient to make component-wise testing compositional.

We tested the MBM method using the Axini Modeling platform by inserting 20 mutants into an example microservice system. In our set of inserted bugs, MBM found more than half of the bugs faster compared to other methods and was slower for none of the bugs.