Using Relational Problems to Teach Property-Based Testing

TL;DR

This paper advocates using relational problems to effectively teach property-based testing (PBT), demonstrating their motivational value and providing methods to evaluate student-generated specifications in educational settings.

Contribution

It introduces relational problems as a new motivating example for PBT education and offers a simple method to assess the accuracy of student specifications.

Findings

Students can successfully apply PBT to relational problems.

Relational problems effectively motivate learning PBT concepts.

A method to evaluate the correctness of student specifications is proposed.

Abstract

Context: The success of QuickCheck has led to the development of property-based testing (PBT) libraries for many languages and the process is getting increasing attention. However, unlike regular testing, PBT is not widespread in collegiate curricula. Furthermore, the value of PBT is not limited to software testing. The growing use of formal methods in, and the growth of software synthesis, all create demand for techniques to train students and developers in the art of specification writing. We posit that PBT forms a strong bridge between testing and the act of specification: it's a form of testing where the tester is actually writing abstract specifications. Inquiry: Even well-informed technologists mention the difficulty of finding good motivating examples for its use. We take steps to fill this lacuna. Approach & Knowledge: We find that the use of "relational" problems -- those for which an input may admit multiple valid outputs -- easily motivates the use of PBT. We also notice that such problems are readily available in the computer science pantheon of problems (e.g., many graph and sorting algorithms). We have been using these for some years now to teach PBT in collegiate courses. Grounding: In this paper, we describe the problems we use and report on students? completion of them. We believe the problems overcome some of the motivation issues described above. We also show that students can do quite well at PBT for these problems, suggesting that the topic is well within their reach. In the process, we introduce a simple method to evaluate the accuracy of their specifications, and use it to characterize their common mistakes. Importance: Based on our findings, we believe that relational problems are an underutilized motivating example for PBT. We hope this paper initiates a catalog of such problems for educators (and developers) to use, and also provides a concrete (though by no means exclusive) method to analyze the quality of PBT.