Testing JavaScript Applications

by Lucas da Costa

Overview

Testing JavaScript Applications teaches you how to implement an automated testing plan for JavaScript-based web applications.

Summary
Automated testing will help you write high-quality software in less time, with more confidence, fewer bugs, and without constant manual oversight. Testing JavaScript Applications is a guide to building a comprehensive and reliable JS application testing suite, covering both how to write tests and how JS testing tools work under the hood. You’ll learn from Lucas de Costa, a core contributor to popular JS testing libraries, as he shares a quality mindset for making testing decisions that deliver a real contribution to your business. You’ll benefit from informative explanations and diagrams, easily-transferable code samples, and useful tips on using the latest and most consolidated libraries and frameworks of the JavaScript ecosystem.

Purchase of the print book includes a free eBook in PDF, Kindle, and ePub formats from Manning Publications.

About the technology
Automated testing is essential to delivering good JavaScript applications every time. A complete testing strategy needs to cover functions in isolation, integration between different parts of your code, and correctness from the end user’s perspective. This book will teach you how to deliver reliable software quickly and confidently.

About the book
Testing JavaScript Applications teaches you how to implement an automated testing plan for JavaScript-based web applications. It describes practical testing strategies, covers useful tools and libraries, and explains how to foster a culture of quality. In this clearly-written, example-rich book, you’ll explore approaches for both backend and frontend applications and learn how to validate your software much more quickly and reliably.

What's inside

Unit, end-to-end, and integration testing
Managing test cost and complexity
Practicing test-driven development
Dealing with external dependencies
Tools like like Jest and Cypress

About the reader
For junior JavaScript developers.

About the author
Lucas da Costa is a core maintainer of Chai and Sinon.JS, two of the most popular testing tools in the JavaScript ecosystem, and contributed to numerous other open-source projects, including Jest.

Table of Contents

PART 1 - TESTING JAVASCRIPT APPLICATIONS

1 An introduction to automated testing

2 What to test and when?

Part 2 - WRITING TESTS

3 Testing techniques

4 Testing backend applications

5 Advanced backend testing techniques

6 Testing frontend applications

7 The React testing ecosystem

8 Testing React applications

9 Test-driven development

10 UI-based end-to-end testing

11 Writing UI-based end-to-end tests

PART 3 - BUSINESS IMPACT

12 Continuous integration and continuous delivery

13 A culture of quality

Product Details

ISBN-13:	9781617297915
Publisher:	Manning
Publication date:	04/13/2021
Pages:	512
Product dimensions:	7.38(w) x 9.25(h) x 1.10(d)

About the Author

Lucas da Costa is a core maintainer of Chai and Sinon.JS, two of the most popular testing tools in the JavaScript ecosystem. He has also contributed to Jest and other relevant open-source projects. Lucas is committed to a culture of sharing and has spoken at major software engineering conferences, including JSConf Colombia, FluentConf, HolyJS, CityJSConf London, and many others.

Table of Contents

Preface xiii

Acknowledgments xv

About this book xvii

About the author xxi

About the cover illustration xxii

Part 1 Testing JavaScript Applications 1

1 An introduction to automated testing 3

1.1 What is an automated test? 4

1.2 Why automated tests matter 9

Predictability 10

Reproducibility 12

Collaboration 13

Speed 15

2 What to test and when? 18

2.1 The testing pyramid 19

2.2 Unit tests 23

2.3 Integration tests 31

2.4 End-to-end tests 37

Testing HTTP APIs 39

Testing GUIs 43

Acceptance tests and end-to-end tests are not the same 44

2.5 Exploratory testing and the value of QA 45

2.6 Tests, cost, and revenue 47

Part 2 Writing Tests 57

3 Testing techniques 59

3.1 Organizing test suites 60

Breaking down tests 65

Parallelism 68

Global hooks 70

Atomicity 71

3.2 Writing good assertions 73

Assertion and error handling 73

Loose assertions 76

Using custom matchers 81

Circular assertions 83

3.3 Test doubles: Mocks, stubs, and spies 85

Mocking imports 96

3.4 Choosing what to test 100

Don't test third-party software 101

To mock, or not to mock: That's the question 102

When in doubt, choose integration tests 104

3.5 Code coverage 105

Automated coverage reports 107

Coverage types 107

What coverage is good for and what it isn't 108

4 Testing backend applications 112

4.1 Structuring a testing environment 113

End-to-end testing 115

Integration testing 119

Unit testing 124

4.2 Testing HTTP endpoints 126

Testing middleware 131

4.3 Dealing with external dependencies 140

Integrations with databases 140

Integrations with other APIs 152

5.1 Eliminating nondeterminism 162

Parallelism and shared resources 163

Dealing with time 167

5.2 Reducing costs while preserving quality 176

Reducing overlap between tests 177

Creating transitive guarantees 181

Turning assertions into preconditions 182

6 Testing frontend applications 185

6.1 Introducing JSDOM 187

6.2 Asserting on the DOM 194

Making it easier to find elements 201

Writing better assertions 204

6.3 Handling events 207

6.4 Testing and browser APIs 217

Testing a localStorage integration 217

Testing a History API integration 221

6.5 Dealing with WebSockets and HTTP requests 234

Tests involving HTTP requests 235

Tests involving WebSockets 240

7 The React testing ecosystem 249

7.1 Setting up a test environment for React 250

Setting up a React application 250

Setting up a testing environment 255

7.2 An overview of React testing libraries 258

Rendering components and the DOM 259

React Testing Library 264

Enzyme 277

The React test renderer 278

8 Testing React applications 281

8.1 Testing component integration 282

Stubbing components 291

8.2 Snapshot testing 295

Snapshots beyond components 305

Serializes 307

8.3 Testing styles 307

8.4 Component-level acceptance tests and component stories 317

Writing stories 318

Writing documentation 326

9 Test-driven development 330

9.1 The philosophy behind test-driven development 332

What test-driven development is 332

Adjusting the size of your iterations 339

Why adopt test-driven development? 342

When not to apply test-driven development 344

9.2 Writing a JavaScript module using TDD 345

9.3 Testing top-down versus testing bottom-up 355

What bottom-up and top-down testing mean 356

How top-down and bottom-up approaches impact a test-driven workflow 357

The pros and cons of bottom-up versus top-down approaches 359

9.4 Balancing maintenance costs, delivery' speed, and brittleness 364

Test-driven implementation 364

Test-driven maintenance 367

9.5 Setting up an environment for TDD to succeed 369

Teamwide adoption 370

Keeping distinct lanes 371

Pairing 373

Supplementary testing 374

9.6 TDD, BDD, validations, and specificationsBDD (behavior-driven development) 375

10 UI-based end to-end testing 380

10.1 What are UI-based end-to-end tests? 381

10.2 When to write each type of test 383

UI-based end-to-end tests 383

Pure end-to-end tests 384

Pure UI tests 385

A note on acceptance testing and this chapter's name 386

10.3 An overview of end-to-end testing tools 387

Selenium 387

Puppeteer 392

Cypress 393

When to choose Cypress 394

11 Writing UI-based end-to-end tests 397

11.1 Your first UI-based end-to-end tests 399

Setting up a test environment 399

Writing your first tests 401

Sending HTTP requests 411

Sequencing actions 413

11.2 Best practices for end-to-end-tests 417

Page objects 417

Application actions 425

11.3 Dealing with flakiness 429

Avoiding waiting for fixed amounts of time 430

Stubbing uncontrollable factors 433

Retrying tests 443

11.4 Running tests on multiple browsers 445

Using a testing framework to run tests within a browser 446

Running UI-based tests in multiple browsers 447

11.5 Visual regression tests 448

Part 3 Business Impact 453

12 Continuous integration and continuous delivery 455

12.1 What are continuous integration and continuous delivery? 457

Continuous integration 457

Continuous delivery 460

12.2 The role of automated tests in a CI/CD pipeline 463

12.3 Version-control checks 464

13 A culture of quality 468

13.1 Using type systems to make invalid states unrepresentable 469

13.2 Reviewing code to catch problems machines can't 474

13.3 Using linters and formatters to produce consistent code 476

13.4 Monitoring your systems to understand how they actually behave 478

13.5 Explaining your software with good documentation 479

Index 483