Gain insights into writing automated tests for React apps with Jest and React Testing Library. Learn about simulating user interactions and testing asynchronous parts to enhance app reliability.

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Jest - lesson 2

Jest with run command

Jest verbose

Jest coverage

Jest snapshot update

Jest react

Jest react-npm start

Jest react-copy

Jest react-C4

Jest react-C6

Jest react start c6

Jest - lesson 2-copy

Jest sandbox

Jest coverage-copy

Jest react-C4-start

Jest react-C4-start-5000

Jest react-npm start-5000

Jest react start c6-5000

Jest react-C8

The skills acquired from this course will allow you to write automated tests on your React app using Jest and React Testing Library, which are the de-facto testing tools for React. These tests will allow you to ship new versions of your app with confidence. The tests will also allow you to increase your release frequency, allowing you to get features to your customers quicker.

You will learn how to write robust tests that are resilient to breaking when code is improved and refactored, reducing maintenance costs.
The course will teach you how to simulate a user interacting with the app. Beyond that, it will also teach you how to robustly test asynchronous parts of the app.

Regular quizzes and exercises will reinforce knowledge throughout the course.

Testing React Apps with Jest and React Testing Library

# Starter project

The project for this lesson is the completed project from the last lesson. In this lesson, we’ll refactor the test to use Jest’s `spyOn` function.

A copy of the project is in the code widget below. Clicking the **“Run”** button executes the tests.

module.exports = {
  presets: [
    ["@babel/preset-env", { targets: { node: "current" } }],
    ["@babel/preset-react", { runtime: "automatic" }],
  ],
};


React

Dart

GoJS React

Typescript React

Vue.js

# Jest's `spyOn` function

The [`jest.spyOn`](https://jestjs.io/docs/jest-object#jestspyonobject-methodname) function allows a method in an object to be mocked. The syntax is:

```javascript
jest.spyOn(object, methodName);
```

At first, this may not seem that useful for React apps consisting of functional code, but let’s go through the full example.

In the `Hello.test.js` file within the test, output `data` to the console. Add the following line at the start of the test:

```javascript
console.log(data);
```

Run the test and look at the console output:

Learn to use Jest’s spyOn function in this lesson.


Introduction

Getting Started with Jest

Using Matchers

Getting Started with React Testing Library

React Testing Library Queries

Firing Events

Mocking

Testing Different Types of Components

Appendix

Using Jest's spyOn Function

Starter project

Jest’s `spyOn` function