react-router-enzyme-context

A helper for mocking react router v4 context and childContextTypes when testing components with Enzyme mount() and shallow().

This package uses React-Router's history module to mock the history. Specifically, we use their memoryHistory module which was designed for use in testing environments.

It creates a context option and a contextChildTypes option that can be used by Enzyme's mount() and shallow() API's to ensure that all descendants of the component being tested have the correct react-router context.

Install

npm install --save-dev react-router-enzyme-context

Quick Usage Example

  const options = new ReactRouterEnzymeContext();
  const wrapper = mount(
    <ClickMe destination="/somehwere/someplace" />,
    options.get()
  );
});

Or...

const options = new ReactRouterEnzymeContext();
const wrapper = mount(
  <ClickMe destination="/somehwere/someplace" />,
  {
    context: options.getContext(),
    childContextTypes: options.getChildContextTypes(),
  }
);

Problem

Let's say you are performing a unit test on a component that uses react-router v4's Link component. When you click on the link, a react-router executes a route, and the component increments a counter that is stored in it's state.

Here is our simple example of a "dumb component" that would be placed within a "container component" that, in turn, is part of a react router route.

import React from 'react';
import PropTypes from 'prop-types';
import { Link } from 'react-router-dom';
import scss from './MyExample.scss';

export default class ClickMe extends React.Component {
  static propTypes = {
    destination: PropTypes.string.isRequired,
  }

  constructor() {
    super();
    this.state = {
      count: 0,
    };

    this.onClick = this.onClick.bind(this);
  }

  onClick() {
    this.setState({
      count: this.state.count += 1,
    });
  }

  render () {
    return (
      <div className={scss.linkWrapper}>
        <Link
          className={scss.link}
          to={this.props.destination}
          onClick={this.onClick}
        >
          Clicked
          <span className={scss.count}>{this.state.count}<span> Times!<span>
        </Link>
      </div>
    )
  }
}

Here is an integration test using jest and enzyme to see if the counter increments.

import React from 'react';
import { mount, configure } from 'enzyme';
import Adapter from 'enzyme-adapter-react-16';

import ClickMe from './ClickMe';

configure({ adapter: new Adapter() });

describe('<ClickMe />', () => {
  it('should increment when clicked', () => {
    const wrapper = mount(<ClickMe destination="/somehwere/someplace" />);
    wrapper.find('.link').simulate('click');
    expect(wrapper.state('count')).toBe(1);
  });  
})

The test above will crash because Enzyme will complain that the Link component must be a descendant of a Router compnent. The react-router library uses React's context feature to pass data between other react-router components. Many React component libraries use context to communicate.

● <Click Me /> › should increment when clicked

   Invariant Violation: You should not use <Link> outside a <Router>

You can go through the trouble of wrapping your <ClickMe> component inside of a <Router>. However, enzyme can only find the state of the root component.

<Router>  // <--- I am now the root
  <ClickMe> // <--- Enzyme can't test my state or props because I'm not the root!
</Router>

Solution

Enzyme lets you specify the context directly when you call mount or shallow. Both mount and shallow have a second optional argument where you can supply context and other things.

Here is an excerpt from the Enzyme documentation:

---

mount(node[, options]) => ReactWrapper

Arguments

1. node (ReactElement): The node to render
2. options (Object [optional]):
3. options.context: (Object [optional]): Context to be passed into the 4. component
4. options.attachTo: (DOMElement [optional]): DOM Element to attach the component to.
5. options.childContextTypes: (Object [optional]): Merged contextTypes for all children of the wrapper.

Returns

• ReactWrapper: The wrapper instance around the rendered output.

---

When you supply the context in this manner, your <ClickMe /> component is still the root! So you can test state and props.

Here is an example using our react-router-enzyme-context module.

import React from 'react';
import { mount, configure } from 'enzyme';
import Adapter from 'enzyme-adapter-react-16';
import ReactRouterEnzymeContext from 'react-router-enzyme-context';

import ClickMe from './ClickMe';

configure({ adapter: new Adapter() });

describe('<ClickMe />', () => {
  it('should increment when clicked', () => {
    const options = new ReactRouterEnzymeContext();
    const wrapper = mount(
      <ClickMe destination="/somehwere/someplace" />,
      options.get()
    );
    wrapper.find('.link').simulate('click');
    expect(wrapper.state('count')).toBe(1);
  });  
})

Simulating props passed via withRouter() HOC

If the component you are testing is directly wrapped by react-router's withRouter() higher order component, you may want to insert the history and location props into your component.

Currently, match is not supported. You'll have to insert those manually.

  import React from 'react';
  import { withRouter } from 'react-router';

  export default withRouter((props) => {
    const location = { props };
    return (
      <div>
        <h1>My Location:</h1>
        <p>{location.pathName}</p>
      </div>
    )
  });

import React from 'react';
import { mount, configure } from 'enzyme';
import Adapter from 'enzyme-adapter-react-16';
import ReactRouterEnzymeContext from 'react-router-enzyme-context';

import WhereAmI from './WhereAmI';

configure({ adapter: new Adapter() });

describe('<WhereAmiI />', () => {
  it('should tell me my current location', () => {
    const mockRouter = new ReactRouterEnzymeContext();
    mockRouter.props().history.go('/new/location');
    const wrapper = mount(
      <WhereAmI {...mockRouter.props()} />
    );
    expect(wrapper.find('p').text()).toBe('/new/location');
  });  
})