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Core Blocks

Every fast-check test is built from the same four pieces:

  1. Arbitraries describe what values to generate. They pair a random generator with a shrinker so that failing inputs collapse back to readable counterexamples.
  2. Properties describe what must hold for those values. A property takes one or more arbitraries and a predicate. It asserts that for any input the predicate stays valid.
  3. Runners describe how to execute the property: how many runs, with what seed, how to report failures, whether to throw or return details.
  4. Plugins describe how to extend runners to make them even more tailored to your needs.

The children below are the reference pages for each block: start with Properties if you have never written one, jump to Arbitraries when you need the right generator and come back to Plugins and Runners when you need to tune execution.

Reference, not tutorial

The Core Blocks pages are the exhaustive reference. If you are looking for a guided, hands-on walkthrough instead, start with the Quick Start tutorial.

Last updated on by Nicolas DUBIEN