Book Image

Mastering React Test-Driven Development - Second Edition

By : Daniel Irvine
Book Image

Mastering React Test-Driven Development - Second Edition

By: Daniel Irvine

Overview of this book

Test-driven development (TDD) is a programming workflow that helps you build your apps by specifying behavior as automated tests. The TDD workflow future-proofs apps so that they can be modified without fear of breaking existing functionality. Another benefit of TDD is that it helps software development teams communicate their intentions more clearly, by way of test specifications. This book teaches you how to apply TDD when building React apps. You’ll create a sample app using the same React libraries and tools that professional React developers use, such as Jest, React Router, Redux, Relay (GraphQL), Cucumber, and Puppeteer. The TDD workflow is supported by various testing techniques and patterns, which are useful even if you’re not following the TDD process. This book covers these techniques by walking you through the creation of a component test framework. You’ll learn automated testing theory which will help you work with any of the test libraries that are in standard usage today, such as React Testing Library. This second edition has been revised with a stronger focus on concise code examples and has been fully updated for React 18. By the end of this TDD book, you’ll be able to use React, Redux, and GraphQL to develop robust web apps.
Table of Contents (26 chapters)
Part 1 – Exploring the TDD Workflow
Part 2 – Building Application Features
Part 3 – Interactivity
Part 4 – Behavior-Driven Development with Cucumber

Conventions used

There are a number of text conventions used throughout this book.

Code in text: Indicates code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles. Here is an example: “In the first test, change the word appendChild to replaceChildren.”

Bold: Indicates a new term, an important word, or words that you see onscreen. For instance, words in menus or dialog boxes appear in bold. Here is an example: “The presenter clicks the Start sharing button.”

Tips or important notes

Appear like this.

Code snippet conventions

A block of code is set as follows:

it("renders the customer first name", () => {  const customer = { firstName: "Ashley" };  render(<Appointment customer={customer} />);  expect(document.body.textContent).toContain("Ashley");});

There are two important things to know about the code snippets that appear in this book.

The first is that some code samples show modifications to existing sections of code. When this happens, the changed lines appear in bold, and the other lines are simply there to provide context:

export const Appointment = ({ customer }) => (  <div>{customer.firstName}</div>);

The second is that, often, some code samples will skip lines in order to keep the context clear. When this occurs, you’ll see this marked by a line with three dots:

if (!anyErrors(validationResult)) {
} else {

Sometimes, this happens for function parameters too:

if (!anyErrors(validationResult)) {
  const result = await window.fetch(...);

Any command-line input or output is written as follows:

npx relay-compiler

JavaScript conventions

The book almost exclusively uses arrow functions for defining functions. The only exceptions are when we write generator functions, which must use the standard function’s syntax. If you’re not familiar with arrow functions, they look like this, which defines a single-argument function named inc:

const inc = arg => arg + 1;

They can appear on one line or be broken into two:

const inc = arg =>
  arg + 1;

Functions that have more than one argument have the arguments wrapped in brackets:

const add = (a, b) => a + b;

If a function has multiple statements, then the body is wrapped in curly braces:

const dailyTimeSlots = (salonOpensAt, salonClosesAt) => {
  return timeIncrements(totalSlots, startTime, increment);};

If the function returns an object, then that object must be wrapped in brackets so that the runtime doesn’t think it’s executing a block:

setAppointment(appointment => ({  ...appointment,  [name]: value }); 

This book makes liberal use of destructuring techniques to keep the code base as concise as possible. As an example, object destructuring generally happens for function parameters:

const handleSelectBoxChange = (
  { target: { value, name } }
) => {

This is equivalent to saying this:

const handleSelectBoxChange = (event) => {
  const target =;
  const value = target.value;
  const name =;

Return values can also be destructured in the same way:

const [customer, setCustomer] = useState({});

This is equivalent to the following:

const customerState = useState({});
const customer = customerState[0];
const setCustomer = customerState[1];