jest-setup-tests.js

import React from 'react';
import Enzyme, { shallow } from 'enzyme';
import Adapter from 'enzyme-adapter-react-16';
import { createSerializer } from 'enzyme-to-json';

// Set the default serializer for Jest to be the from enzyme-to-json
// This produces an easier to read (for humans) serialized format.
expect.addSnapshotSerializer(createSerializer({ mode: 'deep' }));

// React 16 Enzyme adapter
Enzyme.configure({ adapter: new Adapter() });

// Define globals to cut down on imports in test files
global.React = React;
global.shallow = shallow;
global.localStorage = {
    getItem: () => false,
    setItem: () => true,
};
global.document = {
    getElementById: () => 0,
    body: {
        style: {
            marginTop: 0
        }
    }
};

// Use fake timers for async events
jest.useFakeTimers();