test: Add property-based testing with fast-check

packages/nuqs/package.json

@@ -167,6 +167,7 @@
     "@types/react-dom": "catalog:react19",
     "@vitejs/plugin-react": "^4.3.4",
     "@vitest/coverage-v8": "^3.0.9",
+    "fast-check": "^4.0.1",
     "jsdom": "^26.0.0",
     "next": "15.2.4",
     "react": "catalog:react19",

packages/nuqs/src/url-encoding.test.ts

@@ -1,3 +1,4 @@
+import fc from 'fast-check'
 import { describe, expect, test, vi } from 'vitest'
 import { encodeQueryValue, renderQueryString } from './url-encoding'
 
@@ -47,6 +48,24 @@ describe('url-encoding/encodeQueryValue', () => {
     expect(e('kool&thegang')).toBe('kool%26thegang')
     expect(e('a&b=c')).toBe('a%26b=c')
   })
+
+  test.each([
+    { label: 'ASCII', unit: 'binary-ascii' },
+    { label: 'Printable characters', unit: 'grapheme' },
+    { label: 'Full Unicode range', unit: 'binary' },
+    {
+      label: 'Special ASCII characters',
+      unit: fc.constantFrom(...'-._~!$()*,;=:@/?[]{}\\|^')
+    }
+  ] as const)('Property-based fuzzy testing - $label', ({ unit }) => {
+    fc.assert(
+      fc.property(fc.string({ unit }), str => {
+        const search = `?key=${encodeQueryValue(str)}`
+        const expected = new URLSearchParams(search).get('key')
+        expect(expected).toBe(str)
+      })
+    )
+  })
 })
 
 describe('url-encoding/renderQueryString', () => {

packages/nuqs/vitest.setup.ts

@@ -1,8 +1,15 @@
 import * as matchers from '@testing-library/jest-dom/matchers'
 import { cleanup } from '@testing-library/react'
+import fc, { VerbosityLevel } from 'fast-check'
 import { afterEach, expect } from 'vitest'
 
 expect.extend(matchers)
 
 // https://testing-library.com/docs/react-testing-library/api/#cleanup
 afterEach(cleanup)
+
+fc.configureGlobal({
+  numRuns: 1000,
+  verbose: process.env.CI ? VerbosityLevel.None : VerbosityLevel.VeryVerbose,
+  interruptAfterTimeLimit: 5000
+})