@systemfsoftware/oxlint-plugin-property-testing

Enforce the property-testing contract: it.prop / it.effect.prop predicates return a boolean on every path, never call expect/assert, live only in *.property.test.ts files, and import FastCheck only from effect.

fast-check counts undefined as success — a bare return;, a non-boolean return, or falling off the end of a predicate is a silent pass wearing a green checkmark. These rules make the silent failure modes loud.

Rules

| Rule | What it enforces | | -------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | no-silent-return | Every code path of an it.prop / it.effect.prop predicate (including Effect.gen generator bodies) ends in return <boolean>. Flags bare return;, missing returns, and provably non-boolean returns. | | no-assert-in-property | No expect(...), assert*(...), or raw fc.assert/fc.check inside a property predicate. The boolean return IS the verdict. assert* stays correct in normal tests. | | property-file-purity | Property tests live ONLY in *.property.test.ts files (no plain it()/it.effect() or raw fc.assert there), and every other test file contains no FastCheck imports and no it.prop / it.effect.prop calls. The two never mix. | | require-effect-fastcheck | FastCheck is imported as import { FastCheck as fc } from 'effect' — never from the fast-check package, never under another alias (type-only imports exempt). | | no-unbounded-fanout | A collection arbitrary (S.Array, S.Record, fc.array) with no numeric maxLength/maxKeys that reaches a property generator through an exported recipe (a builder invocation such as boundedUnion(...)) is unbounded fan-out — a maxDepth cap bounds depth only. Bounded collections and files listed in the exempt option (basenames) stay silent. | | no-nested-quantification | A property predicate must not quantify over its own generated value and call out again inside that loop — per-case cost then scales with the drawn size rather than the draw count, and a budget tuned on small draws times out on large ones. Iteration over a bound the generator does not control, and a fold whose body calls nothing, stay silent, as do basenames in the exempt option. |

Install

pnpm add -D @systemfsoftware/oxlint-plugin-property-testing

// oxlint.config.ts
import { defineConfig } from 'oxlint'

export default defineConfig({
  jsPlugins: ['@systemfsoftware/oxlint-plugin-property-testing'],
  rules: {
    '@systemfsoftware/oxlint-plugin-property-testing/no-silent-return': 'error',
    '@systemfsoftware/oxlint-plugin-property-testing/no-assert-in-property': 'error',
    '@systemfsoftware/oxlint-plugin-property-testing/property-file-purity': 'error',
    '@systemfsoftware/oxlint-plugin-property-testing/require-effect-fastcheck': 'error',
    '@systemfsoftware/oxlint-plugin-property-testing/no-unbounded-fanout': 'error',
    '@systemfsoftware/oxlint-plugin-property-testing/no-nested-quantification': 'error',
  },
})

Or spread the recommended preset:

import propertyTestingPlugin from '@systemfsoftware/oxlint-plugin-property-testing'
import { defineConfig } from 'oxlint'

export default defineConfig({
  jsPlugins: ['@systemfsoftware/oxlint-plugin-property-testing'],
  rules: {
    ...propertyTestingPlugin.configs.recommended.rules,
  },
})