`next-router-mock`

An implementation of the Next.js Router that keeps the state of the "URL" in memory (does not read or write to the address bar). Useful in tests and Storybook. Inspired by react-router > MemoryRouter.

Works with NextJS v10, v11, and v12.

Install via NPM: npm install --save-dev next-router-mock

Table of Contents generated with DocToc

Usage with Jest
- A fully working Jest example
Usage with Storybook
- A fully working Storybook example
Dynamic Routes
Sync vs Async
Supported Features
- Not yet supported

Usage with Jest

For unit tests, the next-router-mock module can be used as a drop-in replacement for next/router:

jest.mock('next/router', () => require('next-router-mock'));

If you want to mock next/link, you should also include this mock:

jest.mock('next/dist/client/router', () => require('next-router-mock'));

A fully working Jest example

import singletonRouter, { useRouter } from 'next/router';
import NextLink from 'next/link';
import { render, act, fireEvent, screen, waitFor } from '@testing-library/react';
import { renderHook } from '@testing-library/react-hooks';

import mockRouter from 'next-router-mock';


jest.mock('next/router', () => require('next-router-mock'));
// This is needed for mocking 'next/link':
jest.mock('next/dist/client/router', () => require('next-router-mock'));

describe('next-router-mock', () => {
  beforeEach(() => {
    mockRouter.setCurrentUrl("/initial");
  });

  it('supports `push` and `replace` methods', () => {
    singletonRouter.push('/foo?bar=baz');
    expect(singletonRouter).toMatchObject({
      asPath: '/foo?bar=baz',
      pathname: '/foo',
      query: { bar: 'baz' },
    });
  });

  it('supports URL objects with templates', () => {
    singletonRouter.push({
      pathname: '/[id]/foo',
      query: { id: '123', bar: 'baz' },
    });
    expect(singletonRouter).toMatchObject({
      asPath: '/123/foo?bar=baz',
      pathname: '/[id]/foo',
      query: { bar: 'baz' },
    });
  });

  it('mocks useRouter', () => {
    const { result } = renderHook(() => {
      return useRouter();
    });
    expect(result.current).toMatchObject({ asPath: "/initial" });
    act(() => {
      result.current.push("/example");
    });
    expect(result.current).toMatchObject({ asPath: "/example" })
  });

  it('works with next/link', () => {
    render(
      <NextLink href="/example?foo=bar"><a>Example Link</a></NextLink>
    );
    fireEvent.click(screen.getByText('Example Link'));
    expect(singletonRouter).toMatchObject({ asPath: '/example?foo=bar' });
  });
});

Usage with Storybook

For Storybook, you can use <MemoryRouterProvider> to wrap your stories. You can globally wrap all stories by adding this to storybook/preview.js:

import { addDecorator } from "@storybook/react";
import { MemoryRouterProvider } from 'next-router-mock/MemoryRouterProvider';

addDecorator((Story) => <MemoryRouterProvider><Story/></MemoryRouterProvider>);

You can also wrap individual stories with the <MemoryRouterProvider>, allowing you to customize the properties:

export const ExampleStory = () => (
  <MemoryRouterProvider url="/initial-url">
    <NextLink href="/example"><a>Example Link</a></NextLink>
  </MemoryRouterProvider>
);

The MemoryRouterProvider has the following optional properties:

url (string or object) sets the current route's URL to a string or URL object
async enables async mode, if necessary (see section below for details)
Events:
- onPush(url, { shallow })
- onReplace(url, { shallow })
- onRouteChangeStart(url, { shallow })
- onRouteChangeComplete(url, { shallow })

A fully working Storybook example

// example.story.jsx
import NextLink from 'next/link';
import { action } from '@storybook/addon-actions';

import { MemoryRouterProvider } from 'next-router-mock/MemoryRouterProvider';

export const ExampleStory = () => (
  <MemoryRouterProvider
    url="/initial"
    async
    onPush={action('push')}
    onReplace={action('replace')}
    onRouteChangeStart={action('routeChangeStart')}
    onRouteChangeComplete={action('routeChangeComplete')}
  >
    <NextLink href="/example"><a>Example Link</a></NextLink>
  </MemoryRouterProvider>
);

Dynamic Routes

By default, next-router-mock does not know about your dynamic routes (eg. files like /pages/[id].js). To test code that uses dynamic routes, you must add the routes manually, like so:

import mockRouter from "next-router-mock";
import { createDynamicRouteParser } from "next-router-mock/dynamic-routes";

mockRouter.useParser(createDynamicRouteParser([
  // These paths should match those found in the `/pages` folder:
  "/[id]",
  "/static/path",
  "/[dynamic]/path",
  "/[...catchAll]/path"
]));

// Example test:
it('should parse dynamic routes', () => {
  mockRouter.push('/FOO');
  expect(mockRouter).toMatchObject({
    pathname: '/[id]',
    query: { id: 'FOO' }
  });
})

Sync vs Async

By default, next-router-mock handles route changes synchronously. This is convenient for testing, and works for most use-cases.
However, Next normally handles route changes asynchronously, and in certain cases you might actually rely on that behavior. If that's the case, you can use next-router-mock/async. Tests will need to account for the async behavior too; for example:

it('next/link can be tested too', async () => {
  render(<NextLink href="/example?foo=bar"><a>Example Link</a></NextLink>);
  fireEvent.click(screen.getByText('Example Link'));
  await waitFor(() => {
    expect(singletonRouter).toMatchObject({
      asPath: '/example?foo=bar',
      pathname: '/example',
      query: { foo: 'bar' },
    });
  });
});

Supported Features

useRouter()
withRouter(Component)
router.push(url, as, options)
router.replace(url, as, options)
router.pathname
router.asPath
router.query
Works with next/link (see Jest notes)
router.events supports:
- routeChangeStart(url, { shallow })
- routeChangeComplete(url, { shallow })
- hashChangeStart(url, { shallow })
- hashChangeComplete(url, { shallow })

Not yet supported

PRs welcome!
These fields just have default values; these methods do nothing.

router.isReady
router.route
router.basePath
router.isFallback
router.isLocaleDomain
router.locale
router.locales
router.defaultLocale
router.domainLocales
router.prefetch()
router.back()
router.beforePopState(cb)
router.reload()
router.events not implemented:
- routeChangeError
- beforeHistoryChange

mymactive / next-router-mock