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Since nuqs 2, you can unit-test components that use useQueryState(s){:ts} hooks without needing to mock anything, by using a dedicated testing adapter that will facilitate setting up your tests (with initial search params) and asserting on URL changes when acting on your components.

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NuqsTestingAdapter

The NuqsTestingAdapter{:ts} component provides a test environment for components using nuqs hooks. It simulates the URL state management without requiring a real router.

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Basic setup

Wrap your component under test with the NuqsTestingAdapter{:ts}: 
import { NuqsTestingAdapter } from 'nuqs/adapters/testing'
import { render } from '@testing-library/react'

render(
  <NuqsTestingAdapter searchParams="?count=42">
    <YourComponent />
  </NuqsTestingAdapter>
)

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Using withNuqsTestingAdapter

For testing libraries that support wrapper functions, use withNuqsTestingAdapter{:ts}: 
import { withNuqsTestingAdapter } from 'nuqs/adapters/testing'
import { renderHook } from '@testing-library/react'

const { result } = renderHook(() => useTheHookToTest(), {
  wrapper: withNuqsTestingAdapter({
    searchParams: { count: "42" },
  }),
})

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Testing with Vitest

Here is a complete example using Vitest and Testing Library:
counter-button.test.tsx
import { render, screen } from '@testing-library/react'
import userEvent from '@testing-library/user-event'
import { withNuqsTestingAdapter, type OnUrlUpdateFunction } from 'nuqs/adapters/testing'
import { describe, expect, it, vi } from 'vitest'
import { CounterButton } from './counter-button'

it('should increment the count when clicked', async () => {
  const user = userEvent.setup()
  const onUrlUpdate = vi.fn<OnUrlUpdateFunction>()
  render(<CounterButton />, {
    // 1. Setup the test by passing initial search params / querystring:
    wrapper: withNuqsTestingAdapter({ searchParams: '?count=42', onUrlUpdate })
  })
  // 2. Act
  const button = screen.getByRole('button')
  await user.click(button)
  // 3. Assert changes in the state and in the (mocked) URL
  expect(button).toHaveTextContent('count is 43')
  expect(onUrlUpdate).toHaveBeenCalledOnce()
  const event = onUrlUpdate.mock.calls[0]![0]!
  expect(event.queryString).toBe('?count=43')
  expect(event.searchParams.get('count')).toBe('43')
  expect(event.options.history).toBe('push')
})

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Testing with Jest

Since nuqs 2 is an ESM-only package, there are a few hoops you need to jump through to make it work with Jest. This is extracted from the Jest ESM guide.
  1. Add the following options to your jest.config.ts file:
jest.config.ts
const config: Config = {
  // <Other options here>
  extensionsToTreatAsEsm: [".ts", ".tsx"],
  transform: {}
};
  1. Change your test command to include the --experimental-vm-modules flag:
package.json
{
  "scripts": {
    "test": "NODE_OPTIONS=\"$NODE_OPTIONS --experimental-vm-modules\" jest"
  }
}
Adapt accordingly for Windows with cross-env.

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API Reference

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searchParams

The initial search params to use for the test. These can be a query string, a URLSearchParams object or a record object with string values. 
// As a query string
withNuqsTestingAdapter({
  searchParams: '?q=hello&limit=10'
})

// As URLSearchParams
withNuqsTestingAdapter({
  searchParams: new URLSearchParams('?q=hello&limit=10')
})

// As an object
withNuqsTestingAdapter({
  searchParams: {
    q: 'hello',
    limit: '10' // Values are serialized strings
  }
})

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onUrlUpdate

A function that will be called when the URL is updated by the component. It receives an object with:
  • searchParams{:ts}: the new search params as an instance of URLSearchParams{:ts}
  • queryString{:ts}: the new rendered query string (for convenience)
  • options{:ts}: the options used to update the URL
import { type UrlUpdateEvent } from 'nuqs/adapters/testing'

const onUrlUpdate = (event: UrlUpdateEvent) => {
  console.log(event.queryString) // '?count=43'
  console.log(event.searchParams.get('count')) // '43'
  console.log(event.options.history) // 'push' | 'replace'
}

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hasMemory

By default, the testing adapter is immutable, meaning it will always use the initial search params as a base for URL updates. This encourages testing units of behaviour in a single test. To make it behave like framework adapters (which do store the updates in the URL), set hasMemory: true{:ts}, so subsequent updates build up on the previous state: 
withNuqsTestingAdapter({
  searchParams: '?count=0',
  hasMemory: true
})
This memory is per-adapter instance, and so is isolated between tests, but shared for components under the same adapter.

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Advanced options

  • rateLimitFactor{:ts}: By default, rate limiting is disabled when testing, as it can lead to unexpected behaviours. Setting this to 1 will enable rate limiting with the same factor as in production.
  • resetUrlUpdateQueueOnMount{:ts}: clear the URL update queue before running the test. This is true{:ts} by default to isolate tests, but you can set it to false{:ts} to keep the URL update queue between renders and match the production behaviour more closely.
  • autoResetQueueOnUpdate{:ts}: automatically reset the update queue after each URL update. Defaults to true{:ts}.

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Testing custom parsers

If you create custom parsers with createParser{:ts}, you will likely want to test them. Parsers should:
  1. Define pure functions for parse{:ts}, serialize{:ts}, and eq{:ts}.
  2. Be bijective: parse(serialize(x)) === x{:ts} and serialize(parse(x)) === x{:ts}.
To help test bijectivity, you can use helpers defined in nuqs/testing: 
import {
  isParserBijective,
  testParseThenSerialize,
  testSerializeThenParse
} from 'nuqs/testing'

it('is bijective', () => {
  // Passing tests return true
  expect(isParserBijective(parseAsInteger, '42', 42)).toBe(true)
  // Failing test throws an error
  expect(() => isParserBijective(parseAsInteger, '42', 47)).toThrowError()

  // You can also test either side separately:
  expect(testParseThenSerialize(parseAsInteger, '42')).toBe(true)
  expect(testSerializeThenParse(parseAsInteger, 42)).toBe(true)
  // Those will also throw an error if the test fails,
  // which makes it easier to isolate which side failed:
  expect(() => testParseThenSerialize(parseAsInteger, 'not a number')).toThrowError()
  expect(() => testSerializeThenParse(parseAsInteger, NaN)).toThrowError()
})

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Testing parser functions

The helper functions perform the following checks: isParserBijective(parser, serialized, input){:ts} Tests that a parser is bijective by:
  • Serializing the input and comparing to expected serialized value
  • Parsing the serialized value and comparing to expected input value
  • Using the parser’s eq{:ts} function (if provided) for value comparison
testSerializeThenParse(parser, input){:ts} Tests one direction: serialize the input, then parse it back and verify it matches the original input. testParseThenSerialize(parser, serialized){:ts} Tests the other direction: parse the serialized string, then serialize it back and verify it matches the original string.

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Example: Testing a custom hex parser

hex-color.test.ts
import { describe, expect, it } from 'vitest'
import { createParser, parseAsHex } from 'nuqs'
import { isParserBijective } from 'nuqs/testing'

const hexColorParser = createParser({
  parse(query) {
    if (query.length !== 6) return null
    return {
      r: parseAsHex.parse(query.slice(0, 2)) ?? 0x00,
      g: parseAsHex.parse(query.slice(2, 4)) ?? 0x00,
      b: parseAsHex.parse(query.slice(4)) ?? 0x00
    }
  },
  serialize({ r, g, b }) {
    return (
      parseAsHex.serialize(r) +
      parseAsHex.serialize(g) +
      parseAsHex.serialize(b)
    )
  },
  eq(a, b) {
    return a.r === b.r && a.g === b.g && a.b === b.b
  }
})

describe('hexColorParser', () => {
  it('should parse and serialize hex colors', () => {
    const color = { r: 0x66, g: 0x33, b: 0x99 }
    expect(isParserBijective(hexColorParser, '663399', color)).toBe(true)
  })

  it('should return null for invalid input', () => {
    expect(hexColorParser.parse('invalid')).toBe(null)
    expect(hexColorParser.parse('12345')).toBe(null) // too short
    expect(hexColorParser.parse('1234567')).toBe(null) // too long
  })
})
See issue #259 for more testing-related discussions.