Sign in

fast-check

@fast-check.dev
228 followers 27 following 199 posts

🎲 Property-based testing for JavaScript and TypeScript compatible with Vitest, Jest and others · Official website at fast-check.dev · Made with ♥️ by @nicolas.dubien.me

PostsRepliesMedia
fast-check @fast-check.dev · 15/09/2026
🚀 New release on its way: fast-check v4.10.1 Release notes will land shortly at: github.com/dubzzz/fast-check/releas…
020
fast-check @fast-check.dev · 14/09/2026
🫣 Short trailer for v5? Let's have a sneak peek at the upcoming next major version of fast-check!
031
fast-check @fast-check.dev · 13/09/2026
📝 The release note for fast-check 4.10.0 is out! In this version: 🔌 Plugin API preview, 🔌 7 built-in plugins, 🗑️ Deprecation notices to help you prepare for v5! More at: fast-check.dev/blog/2026/09...
fast-check.dev
What's new in fast-check 4.10.0? | fast-check
Let's pave the way for the upcoming v5. fast-check 4.10.0 comes with the idea of easing the migration path to v5. As such, it should be seen as an intermediate version easing the move to v5. It introd...
041
fast-check @fast-check.dev · 11/09/2026
🚀 New release! Version 4.10.0 is out. 🫣 Get prepared for the upcoming v5.
Image to advertise the release of 4.10.0 of fast-check.

It says:
PREPARE FOR v5.
New plugin API and deprecation notices. v5 is still ahead.

Image build with the help of ChatGPT
061
fast-check @fast-check.dev · 11/09/2026
🚀 New release on its way: @fast-check/poisoning v0.3.1 Release notes will land shortly at: github.com/dubzzz/fast-check/releas…
000
fast-check @fast-check.dev · 11/09/2026
🚀 New release on its way: @fast-check/vitest v0.5.0 Release notes will land shortly at: github.com/dubzzz/fast-check/releas…
000
fast-check @fast-check.dev · 11/09/2026
🚀 New release on its way: @fast-check/jest v2.3.0 Release notes will land shortly at: github.com/dubzzz/fast-check/releas…
001
fast-check @fast-check.dev · 11/09/2026
🚀 New release on its way: fast-check v4.10.0 Release notes will land shortly at: github.com/dubzzz/fast-check/releas…
000
fast-check @fast-check.dev · 23/08/2026
🔌 Plugin capabilities coming soon in fast-check. We are currently crafting our first few plugins to confirm the API 🤞 fast-check.dev/docs/core-bl...
131
fast-check @fast-check.dev · 13/08/2026
🏗️ We are currently thinking and shaping a plugin API to make it easier to extend capabilities of fast-check. We hope it could make it as a minor 🤞 More to come soon...
040
fast-check @fast-check.dev · 27/07/2026
⏭️ Iterator's methods being native in JavaScript, we will also reduce our bundle size by dropping our homemade version of them
000
fast-check @fast-check.dev · 23/07/2026
🚀 Release note for fast-check 4.9.0 is out. It's all about performance and rewriting of `entityGraph`. More at: fast-check.dev/blog/2026/07...
021
fast-check @fast-check.dev · 22/07/2026
⏭️ v5 will also be the first ESM-only release of fast-check. PR on its way 🤞 github.com/dubzzz/fast-...
1120
fast-check @fast-check.dev · 19/07/2026
⏭️ In our next major we are gonna make all properties asynchronous. No more questioning about `property` or `asyncProperty` everything will go via `property`.
160
fast-check @fast-check.dev · 17/07/2026
⏭️ In our next major release we are planning to move away from default exports for named ones. ```ts // Valid import in v4 // import fc from 'fast-check' // New way, already supported in v4 import * as fc from 'fast-check' ```
130
Reposted by fast-check
Vladimir @vladimir.berlin · 10/07/2026
`vmThreads` is 30% faster in Vitest 5 for your jsdom tests. It is now a much better alternative to the default forks+jsdom. Vitest 5 also comes with a `vitest doctor` command that will find the best settings for you! As a note, browser mode also becomes ~30% faster, but for different reasons :)
an app with 342 modules + real deps is ~32% faster. 1022 modules + heavier deps is ~28% faster
0579
fast-check @fast-check.dev · 06/07/2026
We have been verified 🥳
020
fast-check @fast-check.dev · 25/06/2026
Fresh new version of pure-rand, our backing library powering every random value we generate in fast-check. npmx.dev/package/pure...
npmx.dev
pure-rand - npmx
Pure random number generator written in TypeScript
120
fast-check @fast-check.dev · 16/06/2026
The next minor is being worked on. Expect a few performance optimisations to land ⚡
110
Reposted by fast-check
Nicolas Dubien @nicolas.dubien.me · 16/06/2026
I'll discuss a little bit about Property Based Testing and @fast-check.dev during the breakout sessions of @webengineshackfest.org (remotely for me)
021
fast-check @fast-check.dev · 04/05/2026
🐒 And now it's fast-check's turn at tangled.org/fast-check.d... So far, just mirrors of @github.com on @tangled.org but stability of GitHub is more and more concerning 😟
tangled.org
fast-check.dev/fast-check
[[MIRROR from GitHub]] Property based testing framework for JavaScript (like QuickCheck) written in TypeScript
1132
fast-check @fast-check.dev · 04/05/2026
🎲 We just started to mirror pure-rand on @tangled.org
npmx.dev
pure-rand - npmx
Pure random number generator written in TypeScript
0142
fast-check @fast-check.dev · 18/04/2026
🚀 fast-check 4.7.0 has recently been released! ✍️ Support for unicode properties in `stringMatching` 🗜️ Reversible values with `json` More details at fast-check.dev/blog/2026/04...
fast-check.dev
What's new in fast-check 4.7.0? | fast-check
Until now, Unicode property escapes of the form \p{...} or \P{...} were not implemented in stringMatching. This release adds support for them so stringMatching can generate matching values directly.
051
Reposted by fast-check
Bjorn Lu @bluwy.me · 14/04/2026
FYI if you use pnpm and upgraded from Vite 7 -> 8, you might still have esbuild installed but unused. You can purge it out by: 1. Set `autoInstallPeers: false` in `pnpm-workspace.yaml` 2. `pnpm i` 3. Undo no1 4. `pnpm i`
1486
fast-check @fast-check.dev · 27/03/2026
🚀 We just released a fresh way lighter version of pure-rand. Install size for each recent version: • 𝟴.𝟰.𝟬: 62.4 kB 🐇 • 𝟴.𝟯.𝟬: 71.6 kB 🐘 • 𝟴.𝟮.𝟬: 53.6 kB 🐜
020
fast-check @fast-check.dev · 27/03/2026
🖇️ Our latest release of @fast-check/vitest added native support for before each/afterEach hooks of @vitest.dev. No more need to manually connect them into fast-check assertions they get automatically integrated if you use our connector package. Connector: npmx.dev/package/@fas...
npmx.dev
@fast-check/vitest - npmx
Property based testing for Vitest based on fast-check
2153
fast-check @fast-check.dev · 27/03/2026
🗜️ We are working on a new release of pure-rand to decrease the bundle impact of our Mersenne Twister jump 🤫 📚 And on fast-check's side we pile a few ideas for a next major that should bring an even faster runtime and more.
000
fast-check @fast-check.dev · 20/03/2026
🎲 New release of pure-rand, our internal dependency. With 33% increase in bundle size but for the right cause: we want to provide users with ways to jump on Mersenne Twister generators. It has been a long PR started 6 years ago and that finally made it.
0131
fast-check @fast-check.dev · 09/03/2026
⚡ fast-check 4.6.0 is here! It comes with: 🗜️ Lighter bundle 🔧 Extra capabilities for stringMatching More details at fast-check.dev/blog/2026/03...
fast-check.dev
What's new in fast-check 4.6.0? | fast-check
Until now, stringMatching had no built-in way to cap the length of the produced strings except applying a manual post-filter on the generated values. This release adds a maxLength constraint to ensure...
0111
fast-check @fast-check.dev · 05/03/2026
🚀 This is it: version 8.0.0 of pure-rand is out! 📦 Lighter bundle 🛢️ No more barrel files 🧹 Simplified API by default npmx.dev/package/pure...
092
fast-check @fast-check.dev · 05/03/2026
👋 Welcome from @eurosky.social
0190
fast-check @fast-check.dev · 28/02/2026
🎲 We are currently making deep changes onto our internal random library called pure-rand. Expects lighter bundle on npm and faster to load at execution time within fast-check
1120
fast-check @fast-check.dev · 26/02/2026
🏃‍♂️ Currently updating all our links to point to @npmx.dev · PRs on their way to update our website fast-check.dev but also all the README files
fast-check.dev
fast-check official documentation | fast-check
fast-check is a Property-based Testing framework for JavaScript and TypeScript. It works with Jest, Mocha, Vitest, and others. Let's fuzz!
0153
fast-check @fast-check.dev · 23/02/2026
🤯 Still impressed to see how simple it is to move from Jest to @vitest.dev We just moved pure-rand, one of the core packages in fast-check
050
fast-check @fast-check.dev · 23/02/2026
⚡ We are currently moving our build chain to @rolldown.rs It's a game changer! Our packages are building really fast now. In the past we were using raw Typescript, but it's not an ideal option to bundle a package even if it works pretty well.
190
fast-check @fast-check.dev · 19/02/2026
⁉️ Is this GitHub action workflow risky? With pull_request alone I have to wait for having manually approved the workflows to run on the PR, pull_request_target seems to be the way to go, but I'm uncomfortable with using it 😬 Anyone to confirm it's safe? github.com/dubzzz/fast-...
github.com
111
fast-check @fast-check.dev · 19/02/2026
🔑 We've just reworked our template for pull requests on @fast-check.dev With the rise of vibe-coding we wanted to take into account this new trend in our checklist that must be completed before opening a PR: github.com/dubzzz/fast-...
github.com
060
Reposted by fast-check
danielroe @danielroe.dev · 07/02/2026
🧪 `@nuxt/test-utils` v4 is out 🚀 👺 mocking is much more reliable ⚡ works with vitest v4 + Vite's native Module Runner ⚗️ registerEndpoint improvements much thanks to github.com/yamachi4416 and @adamdehaven.com ❤️ 👉 github.com/nuxt/test-u... let me know how it goes! 🙏
github.com
Release v4.0.0 · nuxt/test-utils
4.0.0 is the next major release. 👀 Highlights We're releasing Nuxt Test Utils v4, with support for Vitest v4. 🚀 Better mocking support The biggest improvement in this release is how mocking wo...
16910
fast-check @fast-check.dev · 04/02/2026
We are currently deeply reworking our JavaScript testing expert to make it able to deal with a larger variety of tests 🤞 Several new guidelines will be added to help AI agents into proofreading the test they wrote to be critical of themselves before giving you the test.
070
fast-check @fast-check.dev · 04/02/2026
Spread love 💕 Like us on @npmx.dev, npmx.dev/package/fast...
npmx.dev
npmx
051
fast-check @fast-check.dev · 03/02/2026
We are now part of @npmx.dev testing tool-chain. More tests to come.
0191
Reposted by fast-check
Nicolas Dubien @nicolas.dubien.me · 02/02/2026
Am I the only one or is Claude Code from @anthropic.com automatically setting up @fast-check.dev along @vitest.dev when asked to add tests to a project? The prompt was: > add test coverage to this repository, feel free to add the packages you feel relevant to achieve that task No skill added
221
fast-check @fast-check.dev · 01/02/2026
👉 Our testing expert is there: skills.sh/dubzzz/fast-... We will restrict the scope to non-e2e but plan to cover testing-library and playwright. 🙏 Help welcomed ♥️ Share the word and feel free to contribute, the more contributors the better the rules
skills.sh
javascript-testing-expert by dubzzz/fast-check
Discover and install skills for AI agents.
152
fast-check @fast-check.dev · 01/02/2026
🚀 Here is a very first version of our "JavaScript testing expert". There are still a LOT of missing guidelines. We still want to cover basics of UI testing with testing-library and @vitest.dev with @playwright.dev but soon... First let's play with it 🤞
240
fast-check @fast-check.dev · 31/01/2026
🧙‍♂️ We are currently writing down some AI skills for testing in general and some for fast-check itself Hope it could lead to better tests and less bugs 👾
030
fast-check @fast-check.dev · 30/01/2026
🤫 We’re cleaning up our packages and going ESM-only. Reworking the entire build pipeline, moving from pure tsc to Rolldown. 😍 @rolldown.rs is so easy to connect. Amazing how quickly you can get what you need with just a few lines.
010
fast-check @fast-check.dev · 26/01/2026
We’re excited to welcome Mercedes-Benz as a new sponsor of fast-check! 🚀
160
fast-check @fast-check.dev · 23/01/2026
copy and paste the bunny and then put something else in his hand (\_/) (°-°) />🐒>
010
fast-check @fast-check.dev · 22/01/2026
👀 getSeed is probably something we can use to seed fast-check in Vitest context 🤔 vitest.dev/api/advanced...
vitest.dev
Vitest
Next generation testing framework powered by Vite
020
fast-check @fast-check.dev · 18/01/2026
Currently in fast-check, when you check a synchronous predicate the assertion is synchronous but when checking an asynchronous one it becomes asynchronous and requires another helper to be called. What if it was always asynchronous? But with the benefit of always calling fc.property 🤔
132