fast-check
@fast-check.dev
π² Property-based testing for JavaScript and TypeScript compatible with Vitest, Jest and others Β· Official website at https://fast-check.dev Β· Made with β₯οΈ by @nicolas.dubien.me
π fast-check 4.5.0 just got released
ποΈ It adds support for relational structures via a new arbitrary called entityGraph. Give it an erzat of your db schema, it will came up with entities marching it.
π Still more to come for entityGraph, mostly around shrink.
π Next minor might address fuzzing.
ποΈ It adds support for relational structures via a new arbitrary called entityGraph. Give it an erzat of your db schema, it will came up with entities marching it.
π Still more to come for entityGraph, mostly around shrink.
π Next minor might address fuzzing.
December 20, 2025 at 8:42 AM
π fast-check 4.5.0 just got released
ποΈ It adds support for relational structures via a new arbitrary called entityGraph. Give it an erzat of your db schema, it will came up with entities marching it.
π Still more to come for entityGraph, mostly around shrink.
π Next minor might address fuzzing.
ποΈ It adds support for relational structures via a new arbitrary called entityGraph. Give it an erzat of your db schema, it will came up with entities marching it.
π Still more to come for entityGraph, mostly around shrink.
π Next minor might address fuzzing.
Quick release note for 4.4.0 π
fast-check.dev/blog/2025/12...
fast-check.dev/blog/2025/12...
What's new in fast-check 4.4.0? | fast-check
We expand fast-check's collection of arbitraries with two data structures: Map and Set. These native collections are now first-class citizens in fast-check, making it easier to test code that relies o...
fast-check.dev
December 15, 2025 at 2:27 PM
Quick release note for 4.4.0 π
fast-check.dev/blog/2025/12...
fast-check.dev/blog/2025/12...
π Yesterday, we released our new minor, version 4.4.0. It includes a few new arbitraries: for set and map.
The next minor will add support for recursive structures having reused references. We had to drop it at the last minute due to unfixable flows in the original design.
The next minor will add support for recursive structures having reused references. We had to drop it at the last minute due to unfixable flows in the original design.
December 7, 2025 at 8:42 PM
π Yesterday, we released our new minor, version 4.4.0. It includes a few new arbitraries: for set and map.
The next minor will add support for recursive structures having reused references. We had to drop it at the last minute due to unfixable flows in the original design.
The next minor will add support for recursive structures having reused references. We had to drop it at the last minute due to unfixable flows in the original design.
Reposted by fast-check
I'm working on a new built-in arbitrary for @fast-check.dev but so far I'm stuck on typings. I want to be sure I can come up with appropriate typings before moving on with the implementation...
My current version is available at gist.github.com/dubzzz/20452..., but ideally I'd like to...
My current version is available at gist.github.com/dubzzz/20452..., but ideally I'd like to...
Relationship builder in fast-check
Relationship builder in fast-check. GitHub Gist: instantly share code, notes, and snippets.
gist.github.com
December 3, 2025 at 3:51 PM
I'm working on a new built-in arbitrary for @fast-check.dev but so far I'm stuck on typings. I want to be sure I can come up with appropriate typings before moving on with the implementation...
My current version is available at gist.github.com/dubzzz/20452..., but ideally I'd like to...
My current version is available at gist.github.com/dubzzz/20452..., but ideally I'd like to...
Pretty cool feature. It should help us into measuring how costly @fast-check.dev is to load compared to others
Vitest 4.0.15 comes with a cool experimental feature: Imports Breakdown. Every module shows how long it took to load in UI and in the VSCode extension!
Pass down `--experimental.printImportBreakdown` to also see it in your terminal.
vitest.dev/guide/ui.htm...
Pass down `--experimental.printImportBreakdown` to also see it in your terminal.
vitest.dev/guide/ui.htm...
December 2, 2025 at 8:22 PM
Pretty cool feature. It should help us into measuring how costly @fast-check.dev is to load compared to others
π
Last year our second day was about finding duplicated gifts π
π If you haven't try it you can still give it a try this year
π If you haven't try it you can still give it a try this year
πβ¨ Day 2 of #AdventOfPBT 2024 is here! β¨π
Santaβs elves messed up again: duplicates in the gift list are causing chaos. Use fast-check to uncover the flaws and ensure everyone gets what they deserve? ππ΅οΈββοΈ
Dive into the challenge now! π
π fast-check.dev/blog/2024/12...
#Testing #Advent #JavaScript
Santaβs elves messed up again: duplicates in the gift list are causing chaos. Use fast-check to uncover the flaws and ensure everyone gets what they deserve? ππ΅οΈββοΈ
Dive into the challenge now! π
π fast-check.dev/blog/2024/12...
#Testing #Advent #JavaScript
Advent of PBT 2024 Β· Day 2 | fast-check
Christmas is at risk! In their rush to meet tight deadlines, Santaβs elves accidentally introduced bugs into critical algorithms. If these issues arenβt discovered in time, Christmas could be delayed ...
fast-check.dev
December 2, 2025 at 10:15 AM
π
Last year our second day was about finding duplicated gifts π
π If you haven't try it you can still give it a try this year
π If you haven't try it you can still give it a try this year
No new Advent for this year π
But if you're keen on learning Property Based Testing the one from last year is still relevant π
#Advent #Testing #JavaScript
But if you're keen on learning Property Based Testing the one from last year is still relevant π
#Advent #Testing #JavaScript
πβ¨ Advent of PBT 2024 starts today! β¨π
Santaβs elves messed up a sorting algorithm, and Christmas is at risk! Can you find the bugs using fast-check and save the day? π΅οΈββοΈπ§
Join the challenge now! π
π fast-check.dev/blog/2024/12...
#Testing #Advent #JavaScript
Santaβs elves messed up a sorting algorithm, and Christmas is at risk! Can you find the bugs using fast-check and save the day? π΅οΈββοΈπ§
Join the challenge now! π
π fast-check.dev/blog/2024/12...
#Testing #Advent #JavaScript
Advent of PBT 2024 Β· Day 1 | fast-check
Christmas is at risk! In their rush to meet tight deadlines, Santaβs elves accidentally introduced bugs into critical algorithms. If these issues arenβt discovered in time, Christmas could be delayed ...
fast-check.dev
December 1, 2025 at 6:37 AM
No new Advent for this year π
But if you're keen on learning Property Based Testing the one from last year is still relevant π
#Advent #Testing #JavaScript
But if you're keen on learning Property Based Testing the one from last year is still relevant π
#Advent #Testing #JavaScript
A huge thanks from us π
I'm signing the @opensourcepledge.com, it's time to give back to the maintainers of the projects @nuqs.dev depends on.
I just gave 2700β¬ ($3,212) to 18 maintainers & projects I use, love, and want to support.
Happy Thanksgiving! π
nuqs.dev/blog/open-so...
I just gave 2700β¬ ($3,212) to 18 maintainers & projects I use, love, and want to support.
Happy Thanksgiving! π
nuqs.dev/blog/open-so...
Signing the Open Source Pledge | nuqs
Giving back to maintainers of the OSS projects nuqs depends on.
nuqs.dev
November 28, 2025 at 7:28 AM
A huge thanks from us π
Time to answer the survey. If you use fast-check don't forget to put us as a testing tool π
The State of React survey is out!
π survey.devographics.com/en-US/survey...
You know what to do π
π survey.devographics.com/en-US/survey...
You know what to do π
November 19, 2025 at 10:52 PM
Time to answer the survey. If you use fast-check don't forget to put us as a testing tool π
π€Ά No Advent of PBT for this year, but if you have not tried the one of last year probably a good one to do π
πβ¨ Advent of PBT 2024 starts today! β¨π
Santaβs elves messed up a sorting algorithm, and Christmas is at risk! Can you find the bugs using fast-check and save the day? π΅οΈββοΈπ§
Join the challenge now! π
π fast-check.dev/blog/2024/12...
#Testing #Advent #JavaScript
Santaβs elves messed up a sorting algorithm, and Christmas is at risk! Can you find the bugs using fast-check and save the day? π΅οΈββοΈπ§
Join the challenge now! π
π fast-check.dev/blog/2024/12...
#Testing #Advent #JavaScript
Advent of PBT 2024 Β· Day 1 | fast-check
Christmas is at risk! In their rush to meet tight deadlines, Santaβs elves accidentally introduced bugs into critical algorithms. If these issues arenβt discovered in time, Christmas could be delayed ...
fast-check.dev
November 12, 2025 at 9:47 PM
π€Ά No Advent of PBT for this year, but if you have not tried the one of last year probably a good one to do π
If you're ok with it, we can have a room for it on fast-check.dev/docs/ecosyst...
π± Ecosystem | fast-check
Bring additional capabilities to fast-check by leveraging its rich ecosystem of extensions and plugins
fast-check.dev
September 20, 2025 at 2:04 PM
If you're ok with it, we can have a room for it on fast-check.dev/docs/ecosyst...
Reposted by fast-check
Writing tests is hard, and I'm lazy. I'd rather write a few invariants, and let fast-check fuzz test the rest.
That's why I built @βtraversable/valibot-test.
Here it is in action:
That's why I built @βtraversable/valibot-test.
Here it is in action:
September 19, 2025 at 10:09 PM
Writing tests is hard, and I'm lazy. I'd rather write a few invariants, and let fast-check fuzz test the rest.
That's why I built @βtraversable/valibot-test.
Here it is in action:
That's why I built @βtraversable/valibot-test.
Here it is in action:
β¨ Weβre thrilled to welcome our new Gold Sponsor: LambdaTest! π
Your support helps us keep improving fast-check for the whole community π
More about them at www.lambdatest.com
Your support helps us keep improving fast-check for the whole community π
More about them at www.lambdatest.com
September 18, 2025 at 7:49 AM
β¨ Weβre thrilled to welcome our new Gold Sponsor: LambdaTest! π
Your support helps us keep improving fast-check for the whole community π
More about them at www.lambdatest.com
Your support helps us keep improving fast-check for the whole community π
More about them at www.lambdatest.com
We are part of the trusted list π
All the packages affected by this attack had not enabled trusted publishing and provenance.
- The top four packages were all impacted.
- More than half of the top ten packages were affected.
github.com/sxzz/npm-top...
- The top four packages were all impacted.
- More than half of the top ten packages were affected.
github.com/sxzz/npm-top...
September 8, 2025 at 8:18 PM
We are part of the trusted list π
And here is the associated release note: fast-check.dev/blog/2025/09...
September 5, 2025 at 5:49 PM
And here is the associated release note: fast-check.dev/blog/2025/09...
Reposted by fast-check
We also recently moved @fast-check.dev and all associated packages to Trusted Publishing to ensure a safer publication flow π€
The Nx teamβs investigation into last weekβs supply chain attack found the compromise came from a GitHub Actions workflow injection on an outdated branch, exposing the npm token and enabling malicious publishes. All Nx packages now use Trusted Publishing. π
socket.dev/blog/nx-supp...
socket.dev/blog/nx-supp...
Nx Investigation Reveals GitHub Actions Workflow Exploit Led...
Following last weekβs supply chain attack, Nx published findings on the GitHub Actions exploit and moved npm publishing to Trusted Publishers.
socket.dev
September 3, 2025 at 8:52 PM
We also recently moved @fast-check.dev and all associated packages to Trusted Publishing to ensure a safer publication flow π€
New version of fast-check released π
August 29, 2025 at 7:22 PM
New version of fast-check released π
Reposted by fast-check
Did you know that @rolldown.rs supports converting your top-level variables to var?
It seems weird at first, but is actually helpful - and your output is still ESM and modern code!
The transform can improve perf due to avoiding "temporal dead zone" checks of VMs that can cause slowdowns up to 1000%
It seems weird at first, but is actually helpful - and your output is still ESM and modern code!
The transform can improve perf due to avoiding "temporal dead zone" checks of VMs that can cause slowdowns up to 1000%
July 24, 2025 at 3:34 PM
Did you know that @rolldown.rs supports converting your top-level variables to var?
It seems weird at first, but is actually helpful - and your output is still ESM and modern code!
The transform can improve perf due to avoiding "temporal dead zone" checks of VMs that can cause slowdowns up to 1000%
It seems weird at first, but is actually helpful - and your output is still ESM and modern code!
The transform can improve perf due to avoiding "temporal dead zone" checks of VMs that can cause slowdowns up to 1000%
July 18, 2025 at 7:35 PM
I'm pretty sure we could easily adapt the code from github.com/CanadaHonk/p... into an arbitrary in fast-check. It would be awesome π
As it will not only generate code but also reduce it in case of failure.
As it will not only generate code but also reduce it in case of failure.
github.com
July 17, 2025 at 8:40 PM
I'm pretty sure we could easily adapt the code from github.com/CanadaHonk/p... into an arbitrary in fast-check. It would be awesome π
As it will not only generate code but also reduce it in case of failure.
As it will not only generate code but also reduce it in case of failure.
π fast-check 4.2.0 just got released
It offers some new helpers to deal with race condition detection.
It offers some new helpers to deal with race condition detection.
July 5, 2025 at 7:32 AM
π fast-check 4.2.0 just got released
It offers some new helpers to deal with race condition detection.
It offers some new helpers to deal with race condition detection.
πΏ @fast-check.dev just got leveraged by our community to uncover two prototype pollutions in #Zod
π Let's make the ecosystem safer with property based testing π€
π Let's make the ecosystem safer with property based testing π€
May 13, 2025 at 7:03 AM
πΏ @fast-check.dev just got leveraged by our community to uncover two prototype pollutions in #Zod
π Let's make the ecosystem safer with property based testing π€
π Let's make the ecosystem safer with property based testing π€
πΌοΈ Lately we breached several months in a row the quotas of Git LFS on GitHub. It totally blocked our CI until we paid for extra quotas.
Yesterday, we dropped Git LFS from our repository and outsourced heavy assets to another repository that we could fetch from when needed (bundling of the blog).
Yesterday, we dropped Git LFS from our repository and outsourced heavy assets to another repository that we could fetch from when needed (bundling of the blog).
April 27, 2025 at 1:27 PM
πΌοΈ Lately we breached several months in a row the quotas of Git LFS on GitHub. It totally blocked our CI until we paid for extra quotas.
Yesterday, we dropped Git LFS from our repository and outsourced heavy assets to another repository that we could fetch from when needed (bundling of the blog).
Yesterday, we dropped Git LFS from our repository and outsourced heavy assets to another repository that we could fetch from when needed (bundling of the blog).