Overcoming Non-determinism in Testing Smart Devices: A Case Study

This paper presents a case study in “black-box” assessment of a “smart” device where, based only on the user manuals and the instrument itself, we try to build confidence in smart device reliability. To perform the black-box assessment, we developed a test environment which automates the generation of test data, their execution and interpretation of the results. The assessment was made more complex by the inherent non-determinism of the device. For example, non-determinism can arise due to inaccuracy in an analogue measurement made by the device when two alternative actions are possible depending on the measured value. This non-determinism makes it difficult to predict the output values that are expected from a test sequence of analogue input values. The paper presents two approaches to dealing with this difficulty: (1) based on avoidance of test values that could have multiple responses, (2) based on consideration of all possible interpretations of input data. To support the second approach we use advanced modelling and simulation techniques to predict all the likely interpretations and check whether any of them is observed at the smart device output.