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.

Tested with NextJS v13, v12, v11, and v10.

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

Table of Contents generated with DocToc

• Usage with Jest
  • Jest Configuration
  • Jest Example
• Usage with Storybook
  • Storybook Configuration
  • Storybook Example
• Compatibility with next/link
  • Example: next/link with React Testing Library
  • Example: next/link with Enzyme
  • Example: next/link with Storybook
• Dynamic Routes
• Sync vs Async
• Supported Features
  • Not yet supported

Usage with Jest

Jest Configuration

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'));

You can do this once per spec file, or you can do this globally using setupFilesAfterEnv.

Jest Example

In your tests, use the router from next-router-mock to set the current URL and to make assertions.

import { useRouter } from 'next/router';
import { render, screen, fireEvent } from '@testing-library/react';
import mockRouter from 'next-router-mock';

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

const ExampleComponent = ({ href = '' }) => {
  const router = useRouter();
  return (
    <button onClick={() => router.push(href)}>
      The current route is: "{router.asPath}"
    </button>
  );
}

describe('next-router-mock', () => {
  it('mocks the useRouter hook', () => {
    // Set the initial url:
    mockRouter.push("/initial-path");
    
    // Render the component:
    render(<ExampleComponent href="/foo?bar=baz" />);
    expect(screen.getByRole('button')).toHaveText(
      'The current route is: "/initial-path"'
    );

    // Click the button:
    fireEvent.click(screen.getByRole('button'));
    
    // Ensure the router was updated:
    expect(mockRouter).toMatchObject({ 
      asPath: "/foo?bar=baz",
      pathname: "/foo",
      query: { bar: "baz" },
    });
  });
});

Usage with Storybook

Storybook Configuration

Globally enable next-router-mock by adding the following webpack alias to your Storybook configuration.

In .storybook/main.js add:

module.exports = {
  webpackFinal: async (config, { configType }) => {
    config.resolve.alias = {
      ...config.resolve.alias,
      "next/router": "next-router-mock",
    };
    return config;
  },
};

This ensures that all your components that use useRouter will just work in Storybook.

Storybook Example

In your individual stories, you might want to mock the current URL (eg. for testing an "ActiveLink" component), or you might want to log push/replace actions. You can do this by wrapping your stories with the <MemoryRouterProvider> component like so:

// ActiveLink.story.jsx
import { action } from '@storybook/addon-actions';
import { MemoryRouterProvider } from 'next-router-mock/MemoryRouterProvider';
import { ActiveLink } from './active-link';

export const ExampleStory = () => (
  <MemoryRouterProvider url="/active" onPush={action("router.push")}>
    <ActiveLink href="/example">Not Active</ActiveLink>
    <ActiveLink href="/active">Active</ActiveLink>
  </MemoryRouterProvider>
);

The MemoryRouterProvider has the following optional properties:

• url (string or object) sets the current route's URL
• async enables async mode, if necessary (see "Sync vs Async" for details)
• Events:
  • onPush(url, { shallow })
  • onReplace(url, { shallow })
  • onRouteChangeStart(url, { shallow })
  • onRouteChangeComplete(url, { shallow })

Compatibility with next/link

To use next-router-mock with next/link, you must use a <MemoryRouterProvider> to wrap the test component.

Example: next/link with React Testing Library

When rendering, simply supply the option { wrapper: MemoryRouterProvider }

import { render } from '@testing-library/react';
import NextLink from 'next/link';

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

it('NextLink can be rendered', () => {
  render(
    <NextLink href="/example">Example Link</NextLink>, 
    { wrapper: MemoryRouterProvider }
  );
  fireEvent.click(screen.getByText('Example Link'));
  expect(mockRouter.asPath).toEqual('/example')
});

Example: next/link with Enzyme

When rendering, simply supply the option { wrapperComponent: MemoryRouterProvider }

import { shallow } from 'enzyme';
import NextLink from 'next/link';

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

it('NextLink can be rendered', () => {
  const wrapper = shallow(
    <NextLink href="/example">Example Link</NextLink>, 
    { wrapperComponent: MemoryRouterProvider }
  );
  
  wrapper.find('a').simulate('click');
  
  expect(mockRouter.asPath).to.equal('/example')
});

Example: next/link with Storybook

In Storybook, you must wrap your component with the <MemoryRouterProvider> component (with optional url set).

// 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">
    <NextLink href="/example">Example Link</NextLink>
  </MemoryRouterProvider>
);

This can be done inline (as above).
It can also be implemented as a decorator, which can be per-Story, per-Component, or Global (see Storybook Decorators Documentation for details).
Global example:

// .storybook/preview.js
import { MemoryRouterProvider } from 'next-router-mock/MemoryRouterProvider';

export const decorators = [
  (Story) => <MemoryRouterProvider><Story /></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.route
• 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.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