fast-check vs Rapid

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.

Rapid has no write-up on Specifiction yet; its figures are above.