README.md

@ark/fast-check

Generate fast-check arbitraries from ArkType schemas.

Install

Install it alongside fast-check:

pnpm add arktype @ark/fast-check fast-check

Usage

arkToArbitrary accepts an ArkType Type and returns a fast-check Arbitrary that generates values matching that schema:

import { arkToArbitrary } from "@ark/fast-check"
import { type } from "arktype"
import { assert, property } from "fast-check"

const User = type({
	name: "string",
	"age?": "number.integer >= 0"
})

assert(
	property(arkToArbitrary(User), value => {
		const user = User.assert(value)
		return user.age === undefined || user.age >= 0
	})
)

This is useful when you want property-based tests to cover the same input space that your runtime validators accept.

Supported Schemas

@ark/fast-check supports common ArkType definitions including:

• primitive domains like string, number, bigint, boolean, symbol and unknown
• unions and literals
• numeric, string, array and date constraints
• arrays, tuples and variadic tuples
• object structures, optional properties and index signatures
• finite aliases and morph inputs

Unsupported schema combinations throw when creating the arbitrary, so test failures point to the unsupported definition before the property runs.