fast-check vs Gopter

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.

Gopter is a free Go module for property-based testing. It creates properties from conditions and generated inputs, then checks whether those properties hold. Its generators provide more control than Go's testing/quick package and can be composed with operations such as Map, FlatMap, SuchThat, and WithShrinker. When a property fails, shrinkers seek a smaller value that still demonstrates the failure. Gopter also includes a generator for regular-expression matches and supports stateful tests based on arbitrary commands. Properties can run with Go's testing.T through TestingRun, and the gopter/convey package provides helpers for using Gopter inside GoConvey tests. Console and formatted reporters present test results. The project declares Go 1.20 and is distributed under the MIT License. Its documentation covers the gopter, gen, prop, arbitrary, commands, and convey packages. The README identifies two omissions: ScalaCheck's Pretty feature is not provided, and parallel commands are not available yet.