Testing Microcosm

We’ve put a lot of careful planning into making Microcosm easy to test. In this section, we’ll cover our basic testing setup. Additional sections touch on the individual pieces of Microcosm.


Let’s cover a couple of tools that we’ll use throughout the guides.

These are not mandatory. Examples should be easily translatable to your existing testing setup. However we’ve found these tools to be easy to work with and put them forth as recommendations.


Our testing setup centers around Jest, a testing framework by Facebook. We like Jest because it is fast, feature rich, and doesn’t require a lot of setup.

Jest leans on Jasmine, adding additional features and a custom test runner. A test may look something like:

describe('Suite name', function () {
  it("test name", function () {
    let answer = 2 + 2

    // This is an assertion. If the result here is not what we expect,
    // it will throw an error. Jest will tell us when this happens.

Get started with Jest using their installation guide


Enzyme is a testing utility for working with React. It makes it easy to create, manipulate, and traverse React component trees of any size.

A typical test using Enzyme involves setting up a React component, interacting with it, and then asserting some value:

import React from 'react'
import {mount} from 'enzyme'

import Hello from '../components/hello-world'

describe('<Hello />', function () {
  it('it greets a user at a given name', function () {
    let wrapper = mount(<Hello name="Bill" />)
    let text = wrapper.text()

    expect(text).toEqual('Hello, Bill!')

We won’t get into it, but Enzyme can do quite a bit more. It can also simulating events, find DOM elements by their component type, and much more. It has become an essential tool for writing concise UI tests with React.


Testing UI code often means we have to deal with the browser. This can be a frustrating experience. Browser testing takes time, can be flaky, and hog system resources.

To work around this, Jest provides first-class support for jsdom, a JavaScript implementation of the web browser’s Document Object Model (DOM). By using jsdom, we can write unit tests against an environment very similar to the browser without paying in execution time.

Chances are that you already have jsdom if you’ve set up Jest. All that’s required is to tell Jest that you would like to use it:

# Whenever you execute tests, add this flag:
jest --env jsdom

Jest will automatically setup and teardown jsdom for every one of your test suites.

Wrapping up

That’s it! Now that you are familiar with the tools we’ll use in the examples, check out the individual guides for more details.