Model-Based Testing for MQTT Applications

Model-based testing is a widely-used vital technique for testing software running in a complex environment. In this paper, we propose extensions to existing model-based tools to apply this technique to software that employs the MQ Telemetry Transport (MQTT) protocol for transmitting messages, commonly used in the Internet of Things (IoT) environment. First, in the finite state machine used for generating test cases in a model-based testing framework, we introduce a type of transition that is triggered when receiving MQTT messages. Second, we extend the finite-state machine so that it produces test cases that reflect the characteristics of IoT software – a large number of relatively simple devices communicate with servers. Third, the concept of time is introduced into the finite state machine. Naturally, this is necessary for verifying the properties of software that runs for a long time. Moreover, to facilitate such verification, both real-time and virtual time are introduced. We implemented these extensions into a model-based testing tool, Modbat, and conducted a small experiment to confirm the feasibility, gaining positive results.