fast-check official documentation

Testing made easy

Finding bugs has never been so easy! From classical edge cases to very complex combinations of inputs, fast-check is able to detect any class of bug.

Test runner agnostic

fast-check can be used within any test runner without any specific integration needed. It works well with Jest, Mocha, Vitest, and others.

Next level testing

Let fuzzing and generative testing help you into uncovering the most challenging bugs: race conditions, prototype poisoning, zero-days…

test('validates substring presence in concatenated string', () => {
  fc.assert(
    fc.property(fc.string(), fc.string(), fc.string(), (a, b, c) => {
      expect(isSubstring(`${a}${b}${c}`, b)).toBe(true);
    })
  );
});

They trust us…

These projects have been using fast-check for some time now and have found some issues thanks to it!

They spread their love…

Kind messages spreading love around fast-check

fast-check is too good!

Tomer Aberbach

Working on @Google Docs

Can attest, it is awesome!🔥

David Blass

Full-time open source dev and author of @arktypeio, TypeScript's 1:1 validator optimized from editor to runtime⛵

Wrote one property based test with @ndubien's fast check and immediately found & fixed 3 bugs. How is generative testing not mainstream yet?

Adam Berger

♥️ Helping product teams build amazing products with Team Pando: your collaborative space for product requierments

@ndubien's fast-check is unit testing on steroids.

Emilian Bold

Software engineer

So, TypeScript has had a small epidemic of crashes (both my fault 😅), both were very annoying to find and minimize.

I added a fast-check unittest to fuzz the parser and in seconds it found the same bug.

Jake Bailey

Senior Software Engineer at Microsoft working on @typescript

Looks awesome, i need to finally try this out in practice

Mateusz Burzyński

programmer but also a little bit of code-poet wannabe, maintaining XState, Emotion, redux-saga & more, OSS enthusiast, working at @statelyai

They contribute to the project…

People involved at some point in the development of fast-check

They sponsor us…

They financially contribute to the fast-check

You can also become one of them by contributing via GitHub Sponsors or OpenCollective.