Programmable Property-Based Testing

TL;DR

This paper introduces a new programmable property-based testing language that decouples property definitions from execution, enabling rapid prototyping of domain-specific testing frameworks with increased flexibility.

Contribution

It proposes a deeper language for properties using deferred binding abstract syntax, implemented in Rocq and Racket, allowing customizable and domain-specific testing approaches.

Findings

Decoupling properties from runners enhances flexibility.

Rapid prototyping of domain-specific testing frameworks is feasible.

Programmable properties improve testing customization.

Abstract

Property-based testing (PBT) is a popular technique for establishing confidence in software, where users write properties -- i.e., executable specifications -- that can be checked many times in a loop by a testing framework. In modern PBT frameworks, properties are usually written in shallowly embedded domain-specific languages, and their definition is tightly coupled to the way they are tested. Such frameworks often provide convenient configuration options to customize aspects of the testing process, but users are limited to precisely what library authors had the prescience to allow for when developing the framework; if they want more flexibility, they may need to write a new framework from scratch. We propose a new, deeper language for properties based on a mixed embedding that we call deferred binding abstract syntax, which reifies properties as a data structure and decouples them from the property runners that execute them. We implement this language in Rocq and Racket, leveraging the power of dependent and dynamic types, respectively. Finally, we showcase the flexibility of this new approach by rapidly prototyping a variety of property runners, highlighting domain-specific testing improvements that can be unlocked by more programmable testing.