# Testing

URL (HTML): /docs/testing
URL (LLMs): /docs/testing.md
Source: https://raw.githubusercontent.com/47ng/nuqs/refs/heads/next/packages/docs/content/docs/testing.mdx

Some tips on testing components that use `nuqs`


Since nuqs 2, you can unit-test components that use `useQueryState(s)` 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.

## Testing hooks with React Testing Library

When testing hooks that rely on nuqs’ `useQueryState(s)` with React Testing Library’s
[`renderHook`](https://testing-library.com/docs/react-testing-library/api/#renderhook) function,
you can use `withNuqsTestingAdapter` to get a wrapper component to pass to the
`renderHook` call:

```tsx
import { withNuqsTestingAdapter } from 'nuqs/adapters/testing'

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

Available since `nuqs@2.2.0`.

## Testing components with Vitest

Here is an example for Vitest and Testing Library to test a button rendering
a counter:

### Vitest v1

```tsx title="counter-button.test.tsx"
// [!code word:withNuqsTestingAdapter]
import { render, screen } from '@testing-library/react'
import userEvent from '@testing-library/user-event'
import { withNuqsTestingAdapter, type UrlUpdateEvent } 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<[UrlUpdateEvent]>()
  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')
})
```

### Vitest v2

```tsx title="counter-button.test.tsx"
// [!code word:withNuqsTestingAdapter]
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')
})
```

See issue [#259](https://github.com/47ng/nuqs/issues/259) for more testing-related discussions.

## Jest and ESM

Since nuqs 2 is an [ESM-only package](https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c),
there are a few hoops you need to jump through to make it work with Jest.
This is extracted from the [Jest ESM guide](https://jestjs.io/docs/ecmascript-modules).

1. Add the following options to your jest.config.ts file:

```ts title="jest.config.ts"
const config: Config = {
  // <Other options here>
  // [!code highlight:2]
  extensionsToTreatAsEsm: [".ts", ".tsx"],
  transform: {}
};
```

2. Change your test command to include the `--experimental-vm-modules` flag:

```json title="package.json"
// [!code word:--experimental-vm-modules]
{
  "scripts": {
    "test": "NODE_OPTIONS=\"$NODE_OPTIONS --experimental-vm-modules\" jest"
  }
}
```

<Callout>
  Adapt accordingly for Windows with [`cross-env`](https://www.npmjs.com/package/cross-env).
</Callout>

## API

`withNuqsTestingAdapter` accepts the following arguments:

* `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.

```tsx
withNuqsTestingAdapter({
  searchParams: '?q=hello&limit=10'
})

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

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

* `onUrlUpdate`: a function that will be called when the URL is updated
  by the component. It receives an object with:
  * the new search params as an instance of `URLSearchParams`
  * the new rendered query string (for convenience)
  * the options used to update the URL.

* `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`, so subsequent updates
build up on the previous state. This memory is per-adapter instance,
and so is isolated between tests, but shared for components under the same
adapter.

### Internal/advanced options

* `rateLimitFactor`: By default, rate limiting is disabled when testing, as it can lead to unexpected behaviours. Setting this to `1` enables rate limiting with the same factor as in production.
* `resetUrlUpdateQueueOnMount`: clears the URL update queue before running the test. This is `true` by default to isolate tests, but you can set it to `false` to keep the URL update queue between renders and match production behaviour more closely.

## NuqsTestingAdapter

The `withNuqsTestingAdapter` function is a wrapper component factory function
wraps children with a `NuqsTestingAdapter`, but you can also use
it directly:

```tsx
// [!code word:NuqsTestingAdapter]
import { NuqsTestingAdapter } from 'nuqs/adapters/testing'

<NuqsTestingAdapter>
  <ComponentsUsingNuqs/>
</NuqsTestingAdapter>
```

It takes the same props as the arguments you can pass to `withNuqsTestingAdapter`.

## Testing custom parsers

If you create custom parsers with `createParser`, you will likely want to
test them.

Parsers should:

1. Define pure functions for `parse`, `serialize`, and `eq`.
2. Be bijective: `parse(serialize(x)) === x` and `serialize(parse(x)) === x`.

To help test bijectivity, you can use helpers defined in `nuqs/testing`:

```ts
// [!code word:isParserBijective]
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()
})
```

Available since `nuqs@2.4.0`.

---

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