Metamorphic Testing For Machine Learning: Applicability, Challenges, and Research Opportunities

The wide adoption and growth of Machine Learning (ML) have made tremendous advancements in revolutionizing a number of fields i.e., manufacturing, transportation, bio-informatics, and self-driving cars. Its ability to extract patterns from a large set of data and then use this knowledge to make future predictions is beyond the human imagination. However, the complex calculations internally performed in them make these systems suffer from the oracle problem; thus, hard to test them for identifying bugs in them and enhancing their quality. An application not properly tested can have disastrous consequences in the production environment. Metamorphic Testing (MT) has been widely accepted by researchers to address the oracle problem in testing both supervised and unsupervised ML-based systems. However, MT has several limitations (when used for testing ML) that the existing literature lacks in capturing them in a centralized place. Applying MT to test ML-based critical systems without prior knowledge/understanding of those limitations can cost organizations a waste of time and resources. In this study, we highlight those limitations to help both the researchers and practitioners to be aware of them for better testing of ML applications. Our efforts result in making the following contributions in this paper, i) providing insights into various challenges faced in testing ML-based solutions, ii) highlighting a number of key challenges faced when applying MT to test ML applications, and iii) presenting the potential future research opportunities/directions for the research community to address them.