CtrlK
BlogDocsLog inGet started
Tessl Logo
PluginPublic

testland/fast-check-testing

Use whenever the task mentions property-based, generative or invariant tests in JavaScript or TypeScript (fast-check): fc.assert and fc.property, arbitraries and composite inputs, map, chain and filter, shrinking and seeds, with Jest, Vitest or Mocha. Has a worked example to start from.

0.96x
Quality

95%

Does it follow best practices?

Impact

94%

0.96x

Average score across 3 eval scenarios

SecuritybySnyk

Passed

No findings from the security scan

Overview
Quality
Evals
Security
Files

shrinking-and-reproducibility.mdreferences/

fast-check shrinking and reproducibility

When a property fails, fast-check prints the falsifying input + a shrunk minimal version + a seed:

Property failed after 47 tests
{ seed: 1234567890, path: "12:1:0", endOnFailure: true }
Counterexample: [{"id": "abc", "age": -1}]
Shrunk 8 time(s)
Got error: Expected age to be >= 18, got -1

To reproduce, replay with the seed:

fc.assert(
  fc.property(...),
  { seed: 1234567890, path: "12:1:0", endOnFailure: true }
);

The seed/path is the deterministic recipe to re-derive the failure.

For CI, set a fixed seed:

import fc from 'fast-check';
fc.configureGlobal({ seed: process.env.CI ? 42 : Date.now() });

references

arbitraries.md

shrinking-and-reproducibility.md

stateful-and-async.md

SKILL.md

tile.json