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The pages in this section assume you are already comfortable writing a property and running it with fc.assert. They show what happens when you want fast-check to do more than check a single invariant on a single call.

Each page solves a different class of problem that cannot be expressed cleanly as a one-shot property:

  • Model-based testing — when the system under test has state and a bug only shows up after a specific sequence of operations. You describe the legal operations as commands and let fast-check search the space of sequences.
  • Race conditions — when the bug is not in what your async code does but in which order its callbacks resolve. fast-check's scheduler lets you deterministically explore those interleavings.
  • Fuzzing — when you want to keep hunting for counterexamples across runs or beyond the default budget, turning fast-check into a continuous fuzz loop rather than a CI gate.
  • Fake data — when you need large volumes of realistic-looking values outside the property-test context, for seeding environments or staging datasets.

:::tip Want a hands-on walkthrough on race conditions? Race conditions is the reference. If you would rather learn by writing a failing test step by step, the Detect race conditions tutorial covers the same ground interactively. :::

Last updated on by Nicolas DUBIEN