relay modern: how to mock relay for unit testing

Question

Am trying to test react relay modern container, but am having this issue.

TypeError: Cannot read property 'environment' of undefined

Here is the test code:

test('render component', () => {
  const tree = renderer.create(
    <User />,
  ).toJSON();

  expect(tree).toMatchSnapshot();
});

Answer 1

Add the below to __mocks__ folder. Then in the test add jest.mock('react-relay'); to the unit test that needs relay. This will mock out relay and leave just the component to test.

 import React from 'react'; import PropTypes from 'prop-types'; const relayMock = jest.genMockFromModule('react-relay'); const relayChildContextTypes = { relay: PropTypes.object, }; const relayEnvironment = { lookup: jest.fn(), }; const relayContext = { relay: { environment: relayEnvironment, variables: {}, }, }; const relayFragmentProps = { relay: { environment: relayEnvironment, }, }; const relayRefetchProps = { relay: { environment: relayEnvironment, refetch: jest.fn(), }, }; const relayPaginationProps = { relay: { environment: relayEnvironment, hasMore: jest.fn(), loadMore: jest.fn(), isLoading: jest.fn(), }, }; relayMock.__relayEnvironment = relayEnvironment; relayMock.__relayFragmentProps = relayFragmentProps; relayMock.__relayRefetchProps = relayRefetchProps; relayMock.__relayPaginationProps = relayPaginationProps; const makeRelayWrapper = (relayProps) => ( (Comp) => { class HOC extends React.Component { getChildContext() { return relayContext; } render() { return <Comp {...this.props} {...relayProps}/>; } } HOC.childContextTypes = relayChildContextTypes; return HOC; } ); relayMock.QueryRenderer = jest.fn(() => React.createElement('div', null, 'Test')); relayMock.createFragmentContainer = makeRelayWrapper(relayFragmentProps); relayMock.createRefetchContainer = makeRelayWrapper(relayRefetchProps); relayMock.createPaginationContainer = makeRelayWrapper(relayPaginationProps); module.exports = relayMock;

Answer 2

You actually dont need to mock the environment variable at all. What I usually do is add:

export class User

to the classdeclaration of the class that I want to test. (Make sure to keep the export default on your connected version of the same class).

I can then test the component the preferred way by importing the component without the need for relay like so in my test:

 import { User } from '../User'

This removes the need for mocking relay and you can pass in the props cleanly to the component.