The Many Ways to Test Your React App

The Many Ways to  
Test React
All Things Open 2016
#ATO2016
Van J. Wilson
@vanwilson

Who You Are
• Know Javascript
• Already familiar with React
• Know a little bit about testing (vanilla Javascript,
another Javascript library/framework, or even in
another language)
• Want to write better software

How most devs actually test
(Look closely; she’s hitting CTRL-R over and over again.)

Why Write Automated Tests?
https://twitter.com/housecor/status/714430381680775168

Why Write Automated Tests?
https://twitter.com/jjafuller/status/714595373059166208

Beneﬁts of Testing
Testing does …
➡ … help you focus on what’s important in the code
➡ … give you conﬁdence that—if you change
something about the code—it still does the same
stuff it did before
Testing doesn’t …
➡ … prove that your code is “correct”
➡ … guarantee the absence of bugs.

Beneﬁts of Testing
• Defensive driving doesn’t guarantee that you won’t
get in an accident.
• Wearing a seat belt doesn’t guarantee that you
won’t get hurt if you do have an accident.
That doesn’t mean you should not wear a seatbelt
or drive defensively.

“It is a profoundly erroneous truism, repeated
by all copy-books and by eminent people when
they are making speeches, that we should
cultivate the habit of thinking of what we are
doing. The precise opposite is the case.
Civilization advances by extending the number
of important operations which we can perform
without thinking about them. Operations of
thought are like cavalry charges in a battle —
they are strictly limited in number, they require
fresh horses, and must only be made at
decisive moments.”
–Alfred North Whitehead, An Introduction to Mathematics

Test-Driven Development
FAIL
PASSREFACTOR
1. Write Tests
2. Run Tests (TESTS FAIL)
3. Write Code to Make
Tests Pass
4. Run Tests (TESTS PASS) 
5. Refactor (repeat until
you can’t think of
anything else to test)

Test-During Development
CODE
FAILPASS
1. Write Some Code 
2. Write Some Tests
3. Run Tests (TESTS FAIL)
4. Write More Code
5. Run Tests (TESTS PASS) 
6. Refactor (repeat until all
the features and tests
are done)

Kinds of automated testing
• Unit Testing
• Integration Testing
• Functional / Acceptance Testing

Kinds of automated testing
Unit
Integration
Functional
xUnit
Test Harness
Selenium

Why testing React is easy
React apps are meant to be
predictable, 
and consequently they are eminently
testable.

React components ==  
mathematical functions
y = mx +b
where
m is the slope of the line,
x is the x-coordinate,
b is the y-intercept

React Components
• Hierarchical
• Encourage one-way data ﬂow
• Ultimately, just Javascript functions

JSX is functions
const element = (
<h1 className="greeting">
Hello, world!
</h1>
);
const element = React.createElement(
'h1',
{className: 'greeting'},
'Hello, world!'
);

Required ﬁles
"devDependencies": {
"babel": "^6.5.2",
"babel-core": "6.11.4",
"babel-loader": "^6.2.4",
"babel-polyfill": "^6.13.0",
"babel-preset-es2015": "6.9.0",
"babel-preset-react": "6.11.1",
"babel-register": "^6.14.0",
"chai": "^3.5.0",
"chai-enzyme": "^0.5.1",
"chalk": "1.1.3",
"enzyme": "^2.4.1",
"eslint": "3.1.1",
"eslint-loader": "1.4.1",
"expect": "^1.20.2",
"istanbul": "^0.4.5",
"istanbul-instrumenter-loader":
"^0.2.0",
"karma": "^1.2.0",
"karma-chai": "^0.1.0",
"karma-chai-plugins": "^0.7.0",
"karma-chrome-launcher": "^2.0.0",
"karma-cli": "^1.0.1",
"karma-coverage": "^1.1.1",
"karma-firefox-launcher": "^1.0.0",
"karma-junit-reporter": "^1.1.0",
"karma-mocha": "^1.1.1",
"karma-mocha-reporter": "^2.1.0",
"karma-phantomjs-launcher": "^1.0.1",
"karma-sourcemap-loader": "^0.3.7",
"karma-spec-reporter": "0.0.26",
"karma-webpack": "^1.8.0",
"mocha": "^3.0.2",
"nock": "^8.0.0",
"phantomjs-polyfill": "0.0.2",
"phantomjs-prebuilt": "^2.1.12",
"react-addons-test-utils": "^15.3.1",
"redux-mock-store": "^1.1.4",
"sass-loader": "^3.1.2",
"sinon": "^1.17.5",
"webpack": "1.13.1"
}

The real minimum
requirements
• Test Framework
• A DOM
• A test utility library that “speaks React”

An aside: It’s still React,
though
So, we’re going to need a few basic building blocks
in order to:
• Compile JSX
• Transpile ES6 (if you want to use it)
• Bundle the libraries with your code
• Include React and ReactDOM (duh)

Bare-bones React setup
"dependencies": {
"react": "^15.3.1",
"react-dom": "^15.3.1"
},
"babel-core": "^6.14.0",
"babel-loader": "^6.2.5",
"babel-polyfill": "^6.13.0",
"babel-preset-es2015": "^6.14.0",
"babel-preset-react": "^6.11.1",
"live-server": "^1.1.0",
"npm-run-all": "^3.1.0",
"webpack": "^1.13.2"
}
Get it all at:
https://gist.github.com/vjwilson/a040c234c0d6683c1341331f57a81e77

Test Frameworks
• Jasmine - mature, built-in assertions and spies
• Jest - wrapper around Jasmine for React
• Tape - straightforward, traditional paradigm
• Ava - built-in ES2015, concurrent test running
• Mocha - modular, allows (requires) separate
assertion and spy libraries

How to decide? Just ask?

Test Frameworks
• Jasmine - mature, built-in assertions and spies
• Jest
• Tape - straightforward, traditional paradigm
• Ava - built-in ES2015, concurrent test running
• Mocha
npm install —save-dev mocha #(or) jest

A little bait-and-switch
Mocha requires you to choose a separate assertion library

Assertion Libraries
• Assert - built into Node, just require/import
• Expect - basic BDD style, similar to Jasmine
• Should - uber BDD style, bleeding edge
• Chai - can mimic any of the three libraries
• Power-Assert - concentrates on “truthy” values
• UnitJS - similar to Chai

Assertion Libraries
• Assert - built into Node, just require/import
• Expect - basic BDD style, similar to Jasmine
• Should - uber BDD style, bleeding edge
• Chai
• Power-Assert - concentrates on “truthy” values
• UnitJS - similar to Chai
npm install —save-dev chai

Options for a test DOM
• A real browser (Chrome, Firefox, Safari etc)
• PhantomJS (a “headless” browser)
• JSDom
Real browsers or PhantomJS will require some “glue”
in the form of something like Karma.

Options for a test DOM
• A real browser (Chrome, Firefox, Safari etc)
• PhantomJS (a “headless” browser)
• JSDom
npm install —save-dev jsdom

Helper Libraries
• React Test Utils - from Facebook, bare-bones
• React Shallow Testutils - some helper wrappers
• Enzyme - like jQuery, but for tests
• Sinon - spies, mocks, and stubs

Helper Libraries
• React Test Utils
• React Shallow Testutils
• Enzyme
• Sinon
npm install —save-dev react-test-utils react-
shallow-testutils enzyme simon

One more thing… spies
Mocha doesn’t come with a mocking library, so to test
the behavior of functions thoroughly, you’ll need a
mocking library.

One more thing… spies
Sinon is the most popular mocking library for Mocha.
npm install —save-dev sinon

Where Do Tests Go?
In their own folder With the code they are testing

Enough setup…
Let’s run some tests!

The Example App
https://github.com/vjwilson/many-ways-to-test-react

Ex1: ES5
• React.createClass (ES5) style components
• Webpack/Babel compiles JSX to a static bundle
• Live Server serves and auto-refreshes the page
• No tests yet (Test-During Development)

Ex1: The App component
var App = React.createClass({
getInitialState: function() {
return {
castMembers: this.props.initialCastMembers,
user: this.props.initialUser
};
},
loginAction: function() {
this.setState({ user: this.props.initialUser });;
},
logoutAction: function() {
this.setState({ user: null });;
},
ex1-react-es5/src/App.js (excerpt)

Ex1: App (cont.)
render: function() {
return (
<div className="container">
<Header user={this.state.user} login={this.loginAction} 
logout={this.logoutAction} />
<Jumbotron />
<div className="panel panel-default">
<div className="panel-heading">
<h2 className="panel-title">Top-Billed Cast</h2>
</div>
<div className="panel-body">
<CastMemberList members = {this.state.castMembers} />
</div>
</div>
</div>
);
}
});

Ex2: Mocha and  
React Test Utils
• Mocha test framework
• JSDom
• React Test Utils (and a little Shallow Tests Utils)
• Chai’s expect function
• Sinon for function spies

Ex2: What changed in
the tooling
"scripts": {
// build stuff …
"test": "mocha --reporter spec test/helpers/testSetup.js  
"test/**/*.test.js"",
"test:watch": "npm run test -- --watch"
},
// other dependencies …
"chai": "^3.5.0",
"jsdom": "^9.5.0",
"mocha": "^3.0.2",
"react-addons-test-utils": "15.0.2",
"react-shallow-testutils": "^2.0.0",
"sinon": "^1.17.6",
}
ex2-mocha-react-test-utils/package.json (excerpt)

Ex2: Test Setup
require(‘babel-register')();
var jsdom = require('jsdom').jsdom;
var exposedProperties = ['window', 'navigator', 'document'];
global.document = jsdom('');
global.window = document.defaultView;
Object.keys(document.defaultView).forEach((property) => {
if (typeof global[property] === 'undefined') {
exposedProperties.push(property);
global[property] = document.defaultView[property];
}
});
global.navigator = {
userAgent: 'node.js'
};
documentRef = document;
ex2-mocha-react-test-utils/test/helpers/testSetup.js (excerpt)

Ex2: Test Setup (cont.)
{
"presets": [
"react",
"es2015"
]
}
ex2-mocha-react-test-utils/.babelrc (excerpt)

Ex2: Components and Tests
!"" src
#   !"" App.js
#   !"" CastMember.js
#   !"" CastMemberList.js
#   !"" Header.js
#   !"" Jumbotron.js
#   $"" index.js
!"" test
#   !"" helpers
#   #   $"" testSetup.js
#   !"" App.test.js
#   !"" CastMember.test.js
#   !"" CastMemberList.test.js
#   !"" Header.test.js
#   $"" Jumbotron.test.js

React Test Utils
• Replaces ReactDOM
• Can renderIntoDocument() or “shallow render”
• Functions to ﬁnd rendered nodes (e.g.):
• scryRenderedDOMComponentsWithClass()
• findRenderedDOMComponentWithClass()
• Simulate() to ﬁre DOM events
• Function to test nodes (e.g.):
• isElementOfType()
• isCompositeComponentWithType()

Ex2: What a Test Looks Like
var chai = require('chai');
var React= require('react');
var TestUtils = require('react-addons-test-utils');
var CastMember = require('../src/CastMember');
const expect = chai.expect;
function setup(props) {
let renderer = TestUtils.createRenderer();
renderer.render(<CastMember {...props}/>);
let output = renderer.getRenderOutput();
return {
props,
output,
renderer
};
}
ex2-mocha-react-test-utils/test/CastMember.test.js (part 1 of 3)

describe('CastMember component', () => {
let props = {
member: {
id: 3,
name: 'Testy McTestface',
imageUrl: 'test-image.jpg',
thumbnailUrl: 'test-image-small.jpg',
bio: 'This is a test.'
}
};
it('should render a div with correct class', () => {
const {output} = setup(props);
expect(output.type).to.equal('div');
expect(output.props.className).to.equal('media');
});

it('should contain two child divs with appropriate classes', () => {
const {output} = setup(props);
const firstChild = output.props.children[0];
const secondChild = output.props.children[1];
expect(firstChild.type).to.equal('div');
expect(firstChild.props.className).to.equal('media-left');
expect(secondChild.type).to.equal('div');
expect(secondChild.props.className).to.equal('media-body');
});
it('should contain a heading element', () => {
const output = TestUtils.renderIntoDocument(<CastMember 
{...props} />);
const titleElement = 
TestUtils.findRenderedDOMComponentWithClass(output, 'media-heading');
expect(TestUtils.isDOMComponent(titleElement)).to.be.true;
});
});

99 Problems with React Test Utils
• Limited API
• Verbose function names
• Too subtle and obtuse
• What is scrying, anyway?
• Brittle and hard to pinpoint elements
• var loginBlock = 
output.props.children.props.children[1] 
.props.children[2].props.children; 
// Wut?

Shallow Test Utils
// other imports…
var ShallowTestUtils = require('react-shallow-testutils');
var Header= require(‘../src/Header');
// other tests…
it('should render a nav with username and logout link if user 
logged in', () => {
props.user = user;
var output = setup(props);
var navbarText = ShallowTestUtils.findWithClass(output,  
'navbar-text');
var navbarLink = ShallowTestUtils.findWithClass(output, 
'navbar-link');
expect(navbarText.props.children).to.equal('Welcome, 
' + user.username);
expect(navbarLink.props.children).to.equal('Logout');
});
ex2-mocha-react-test-utils/test/Header.test.js (excerpt)

Enzyme
• Extends React Test Utils
• Can render a React DOM, shallow-render in
element, or render the ﬁnal HTML DOM
• Has a ton of jQuery-like selectors and helpers
• <renderedOutput>.find(selector)
• <renderedOutput>.findWhere(fn)
• <renderedOutput>.text()
• <renderedOutput>..prop(key)
• and many, many more…
• https://github.com/airbnb/enzyme

Ex3: Mocha and  
Enzyme
"scripts": {
// build stuff …
"test": "mocha --reporter spec test/helpers/testSetup.js  
"src/**/*.test.js"",
"test:watch": "npm run test -- --watch"
},
// other dependencies …
"chai": “^3.5.0",
"enzyme": "^2.4.1",
"jsdom": "^9.5.0",
"mocha": "^3.0.2",
"react-addons-test-utils": "15.0.2",
"react-shallow-testutils": "^2.0.0",
"sinon": "^1.17.6",
}
ex3-mocha-react-test-utils/package.json (excerpt)

Ex3: Components with Tests
!"" src
#   !"" App
#   #   !"" App.js
#   #   $"" App.test.js
#   !"" Cast
#   #   !"" tests
#   #   !"" CastMember.js
#   #   $"" CastMemberList.js
#   !"" Header
#   #   !"" Header.js
#   #   $"" Header.test.js
#   !"" Jumbotron
#   #   !"" Jumbotron.js
#   #   $"" Jumbotron.test.js
#   $"" index.js
!"" test
#   $"" helpers
#   $"" testSetup.js

import React from 'react';
import { expect } from 'chai';
import { shallow, mount, render } from 'enzyme';
import sinon from 'sinon';
import Header from './Header';
describe('Header component', function() {
let props;
beforeEach(function() {
props = {
user: null,
login: function() {},
logout: function() {}
};
});
ex3-mocha-enzyme/src/Header/Header.test.js (excerpts, 1 of 4)

it('should render the static component', function() {
// sanity-check test
// does it "render without exploding"?
// see: https://gist.github.com/thevangelist/ 
e2002bc6b9834def92d46e4d92f15874
const shallowOutput = shallow(<Header user={props.user} 
login={props.loginAction} logout={props.logoutAction} />);
expect(shallowOutput).to.have.length(1);
});
// more tests

describe('calling the appropriate action props', function() {
let loginAction;
let logoutAction;
loginAction = sinon.spy();
logoutAction = sinon.spy();
props.loginAction = loginAction;
props.logoutAction = logoutAction;
});

it('should call login function if no authenticated use', function() {
const shallowOutput = shallow(<Header user={props.user}
const authLink = shallowOutput.find('.login-block .navbar-link');
authLink.simulate('click');
expect(loginAction.calledOnce).to.be.true;
});
it('should call logout function when there is an authenticated user',
function() {
props.user = {
id: 3,
username: 'gmtester'
};
const shallowOutput = shallow(<Header user={props.user}
const authLink = shallowOutput.find('.login-block .navbar-link');
authLink.simulate('click')
expect(logoutAction.calledOnce).to.be.true;
});
});

Ex4: Mocha and  
Enzyme, but in ES6
module: {
loaders: [
{
test: /.js$/,
exclude: /node_modules/,
loader: 'babel-loader',
query: {
presets: ['react']
}
},
]
}
ex1-react-es5/webpack.conﬁg.js (excerpt)
module: {
loaders: [
{
test: /.js$/,
exclude: /node_modules/,
loader: 'babel-loader',
query: {
presets: ['es2015',
'react']
}
},
]
}
ex2-mocha-react-test-utils/webpack.conﬁg.js 
(excerpt)

Remember this poll?
9% usage?!?

Before / After  
Jest-pocalype
• Auto-mocking on by
default
• Optimized inside
Facebook, but not by
default in open source
setup
• Slow
< v15.0 v15.0+
• Auto-mocking off by
default
• New commitment to
community
• Snapshot testing (v14)
• Fast

Ex5: Mocha and  
Jest
• Jest test framework
• JSDom (included with Jest)
• expect function (included with Jasmine2, which is
included with Jest)
• Spies (that’s right, included with Jasmine2, which is
included with Jest)

Ex5: Tests in separate folder
!"" __tests__
#   !"" __snapshots__
#   #   !"" App.test.js.snap
#   #   !"" CastMember.test.js.snap
#   #   !"" CastMemberList.test.js.snap
#   #   !"" Header.test.js.snap
#   #   $"" Jumbotron.test.js.snap
#   !"" App.test.js
#   !"" CastMember.test.js
#   !"" CastMemberList.test.js
#   !"" Header.test.js
#   $"" Jumbotron.test.js
!"" src
#   !"" App
#   #   $"" App.js
#   !"" Cast
#   #   !"" CastMember.js
#   #   $"" CastMemberList.js
#   !"" Header
#   #   $"" Header.js
#   !"" Jumbotron
#   #   $"" Jumbotron.js
#   $"" index.js

import renderer from 'react-test-renderer';
import CastMember from '../src/Cast/CastMember';
test('CastMember rendered static HTML', () => {
const props = {
member: {
id: 3,
name: 'Testy McTestFace',
imageUrl: 'test-image.jpg',
thumbnailUrl: 'test-image-small.jpg',
bio: 'This is a test.'
}
};
ex5-jest/__tests__/CastMember.test.js (part 1 of 2)

const component = renderer.create(
<CastMember {...props} />
);
let tree = component.toJSON();
expect(tree).toMatchSnapshot();
});
ex5-jest/__tests__/CastMember.test.js (part 2 of 2)

One big advantage for Jest
Jest comes set up when you create a
React app with
create-react-app,
Facebook’s React generator

Ex6: Mocha Enzyme, ES6,
and React-Router
• JSDom
• Enzyme
• React-Router

Ex6: React-Router folder structure
!"" src
#   !"" App
#   !"" Cast
#   !"" Header
#   !"" Home
#   !"" Jumbotron
#   !"" Tickets
#   !"" castMemberData.js
#   !"" index.js
#   !"" initialUserData.js
#   !"" routes.js
#   !"" routes.test.js
#   $"" seatData.js
!"" test
#   !"" fixtures
#   $"" helpers

import { shallow, mount } from 'enzyme';
import sinon from 'sinon';
import BuyTicketsPage from './BuyTicketsPage';
import SeatingChart from './Seating/SeatingChart';
import TicketForm from './TicketForm';
import mockSeatData from '../../test/fixtures/mockSeatData';
describe('BuyTicketsPage component', function() {
let routeObject;
routeObject = {
initialSeatData: []
};
});
ex6-mocha-enzyme-es6-react-router/src/Tickets/BuyTicketsPage.test.js (excerpts, 1 of 6)

describe('rendering', function() {
it('should render the component (smoke test)', function() {
const shallowOutput = shallow(<BuyTicketsPage  
route={routeObject} />);
expect(shallowOutput).to.have.length(1);
});
it('should render an element with correct classes',  
function() {
const shallowOutput = shallow(<BuyTicketsPage  
expect(shallowOutput.hasClass('text-center')).to.be.true;
});
});
//…

describe('BuyTicketsPage component actions', function() {
it('should handle a form submission from its TicketForm  
component (manual test)', function() {
routeObject.initialSeatData =  
JSON.parse(JSON.stringify(mockSeatData));
const buyTicketsPage = mount(<BuyTicketsPage  
// manually set the state of selected seats and the  
package to buy
let seatsToSelect =  
routeObject.initialSeatData[2].slice(0, 2);
seatsToSelect[0].selected = true;
seatsToSelect[1].selected = true;

buyTicketsPage.setState({
ticketPackage: {
seats: seatsToSelect
}
});
const ticketForm = buyTicketsPage.find('.ticket-form');
ticketForm.simulate('submit');
const seatArray = buyTicketsPage.state('seatData');
const ticketPackage =  
buyTicketsPage.state('ticketPackage');
expect(seatArray[2][0].sold).to.be.true;
expect(ticketPackage.seats).to.have.lengthOf(0);
});

it('should handle a form submission from its TicketForm
component (automatic test)', function() {
routeObject.initialSeatData =
JSON.parse(JSON.stringify(mockSeatData));
const buyTicketsPage = mount(<BuyTicketsPage
// automatically set the state of selected seats and the  
package to buy
const pageInstance = buyTicketsPage.instance();
pageInstance.updateSeatStatus('C1');
pageInstance.updateSeatStatus('C2');

const ticketForm = buyTicketsPage.find('.ticket-form');
ticketForm.simulate('submit');
const seatArray = buyTicketsPage.state('seatData');
const ticketPackage =
buyTicketsPage.state('ticketPackage');
expect(ticketPackage.seats).to.have.lengthOf(0);
});

Ex7: Mocha Enzyme, ES6,
React-Router, and Redux
• JSDom
• Enzyme
• React-Router
• Redux

Ex7: Redux folder structure!"" src
#   !"" actions
#   #   !"" actionTypes.js
#   #   !"" castMemberActions.js
#   #   !"" seatActions.js
#   #   !"" seatActions.test.js
#   #   !"" userActions.js
#   #   $"" userActions.test.js
#   !"" components
#   !"" reducers
#   #   !"" castMembersReducer.js
#   #   !"" castMembersReducer.test.js
#   #   !"" index.js
#   #   !"" initialState.js
#   #   !"" initialState.test.js
#   #   !"" seatReducer.js
#   #   !"" seatReducer.test.js
#   #   !"" userReducer.js
#   #   $"" userReducer.test.js
#   !"" selectors
#   #   !"" selectors.js
#   #   $"" selectors.test.js
#   !"" store
#   #   $"" configureStore.js
!"" test
#   !"" fixtures
#   #   !"" mockCastMemberData.js
#   #   $"" mockSeatData.js

import seatReducer from './seatReducer';
import * as actions from '../actions/seatActions';
import mockSeatData from '../../test/fixtures/mockSeatData';
import * as types from '../actions/actionTypes';
describe('Seat reducer', function() {
let seats;
seats = JSON.parse(JSON.stringify(mockSeatData));
});
it('should load seats', function() {
const initialState = [];
const action = actions.loadSeats(seats);
const newState = seatReducer(initialState, action);
const expectedSeats = JSON.parse(JSON.stringify(mockSeatData));
expect(newState).to.equal(seats);
});
ex7-mocha-enzyme-es6-react-router-redux/src/reducers/seatReducer.test.js (part 1 of 3)

it('should mark a seat as selected', function() {
const initialState = seats;
const seat = initialState[0][2]; // mock seat A3
const expectedState =  
JSON.parse(JSON.stringify(initialState));
expectedState[0][2].selected = true;
const action = actions.toggleSeatSelected(seat);
// .eql instead of .equal,
// to compare the contents, instead of the reference
expect(newState).to.eql(expectedState);
});

it('should mark a seat as sold', function() {
const initialState = seats;
const seat = seats[0][2]; // mock seat A3
seat.selected = true;
const expectedState = JSON.parse(JSON.stringify(seats));
expectedState[0][2].sold = true;
expectedState[0][2].selected = false;
const action = actions.markSeatSold(seat);
// .eql instead of .equal,
// to compare the contents, instead of the reference
expect(newState).to.eql(expectedState);
});
});

Ex7: The Code Under Test
import * as types from '../actions/actionTypes';
import initialState from './initialState';
export default function seatReducer(state = initialState.seats, 
action) {
let newState;
switch(action.type) {
case types.LOAD_SEATS:
return action.seats;
break;
ex7-mocha-enzyme-es6-react-router-redux/src/reducers/seatReducer.js (part 1 of 3)

case types.TOGGLE_SEAT_SELECTED:
newState = state.map((row) => {
return row.map((seat) => {
if (seat.seatNumber === action.seat.seatNumber) {
const updatedSeat = Object.assign({}, seat);
updatedSeat.selected = !updatedSeat.selected;
return updatedSeat;
} else {
return seat;
}
});
});
return newState;
break;

case types.MARK_SEAT_SOLD:
newState = state.map((row) => {
return row.map((seat) => {
if (seat.seatNumber === action.seat.seatNumber) {
const updatedSeat = Object.assign({}, seat);
updatedSeat.selected = false;
updatedSeat.sold = true;
return updatedSeat;
} else {
return seat;
}
});
});
return newState;
break;
default:
return state;
}
}

Resources
• https://facebook.github.io/react/docs/test-utils.html 🚫
• https://github.com/airbnb/enzyme
• https://semaphoreci.com/community/tutorials/testing-
react-components-with-enzyme-and-
mocha#comments
• https://facebook.github.io/jest/
• https://egghead.io/courses/react-testing-cookbook

Contact
• @vanwilson on Twitter
• van@vanwilson.info
• vanwilson.info (where I blog once or twice a year)

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