fast-check vs QCheck
fast-check
fast-check.devQCheck
github.comSide by side
| Figure | fast-check | QCheck |
|---|---|---|
| Price from | Free | Free |
| Free plan | Yes | Yes |
| Free trial | — | — |
| Open source | Yes | — |
| Web | Yes | — |
| Linux | Yes | Yes |
| API | Yes | — |
| Self-hosted | Yes | — |
| Plans published | 1 | 1 |
| Spec score · Property-Based Testing Tools | 8.9 (#1) | 7.9 (#9) |
| Integrations | The ecosystem lists official integrations for AVA, Jest, and Vitest, along with connectors for libraries such as Zod and io-ts. | The project provides integration layers for OUnit and Alcotest, and the README describes using QCheck with Rely through an npm package. |
| Model-based testing | The API includes modelRun, asyncModelRun and scheduledModelRun functions for model and real-system testing. | The README points to the multicoretests repository for qcheck-stm, which runs sequential and parallel model-based tests, and qcheck-lin, which tests sequential consistency. |
| Purpose | fast-check is a property-based testing library for JavaScript and TypeScript that generates inputs, runs assertions over many cases, and shrinks failures to smaller counterexamples. | QCheck is a QuickCheck-inspired property-based testing library for OCaml. |
Plans
In their own words
fast-check
fast-check is a property-based testing library for JavaScript and TypeScript. It generates inputs and checks expected behavior across many cases, then reduces a failure to a smaller counterexample to help investigate it. Tests combine arbitraries that create values, properties that describe behavior, runners that execute checks, and plugins that extend runners. It works with Jest, Mocha, Vitest, Ava, Bun, Deno, the Node.js test runner, and other test runners. Runs can be configured with seeds, generated-value sizes, time limits, and result reporting globally or per assertion. fast-check supports stateful testing and reproducible failures; its project also describes fuzzing and generative testing for issues such as race conditions and prototype poisoning. The project is open source under the MIT license, and the listed plan is free. Version 5.x requires Node.js 22.12.0 or later and ECMAScript 2025; TypeScript 5.8 or later is optional.
QCheck
QCheck is a property-based testing library for OCaml, inspired by QuickCheck. Rather than relying only on hand-picked examples, it provides combinators to generate values such as lists, arrays, tuples, recursive types, and algebraic types for checking properties. When a check fails, generators can be paired with printers and shrinkers to show and reduce counterexamples. QCheck2 builds shrinking into its generators, though the project describes that API as less battle-tested than QCheck. The package family includes qcheck-core, qcheck-ounit, qcheck-alcotest, qcheck, and ppx_deriving_qcheck; the last can derive generators from type declarations. Runner options include QCheck_base_runner in qcheck-core and QCheck_runner with OUnit compatibility in qcheck, with integration layers for OUnit and Alcotest. The project also points to qcheck-stm for sequential and parallel model-based tests and qcheck-lin for sequential consistency testing. Installation is available through opam, and the source can be built with make. The minimal qcheck-core package depends only on unix and dune. QCheck is free and licensed under BSD-2-Clause.