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.

Testing React Apps with Jest and React Testing Library_468 x 60 copy 3.png

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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 contains a `Hello` component that renders *“Hello”* and a user’s name. The user’s name is retrieved from a web API request. The project also contains a test to verify that the message includes the user’s name.

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

Run the test. 

Does the test pass or fail? Why?

The test fails because it encounters an error when the `fetch` function is called because it is `undefined`. The `fetch` function is `undefined` because it doesn’t exist in JSDOM, which is the implementation of the DOM that Jest uses. Even if `fetch` was implemented, the test would fail because `https://some-server` doesn’t exist.

In this lesson, we'll resolve the failing test by providing an alternate implementation of the `getUser` function.

# Manually mocking a function

Open the `Hello.test.js` file. The test is as follows:

```jsx
test("Should include users name when rendered", async () => {
  render(<Hello id={1} />);

  expect(await screen.findByText(/Bob/)).toBeInTheDocument();
});
```

We need to provide an alternate implementation of the `getUser` function before `render` is called. Before we can provide an alternate implementation of `getUser`, we need to import it into the test file. Add the following import statement to the test file under the existing import statements:

```javascript
import { getUser } from "./data";
```

Add the following alternate implementation of `getUser` in the test, before the call to `render`:

```javascript
getUser = (id) => {
  return new Promise((resolve) =>
    resolve({
      id,
      name: "Bob",
    })
  );
};
```

This function returns a user object in a resolved promise.

Run the test. Does the test pass?

Learn to manually mock a function without employing Jest’s mocking features. 

Mocking a Function without Jest

Learn to manually mock a function without employing Jest’s mocking features.

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

Mocking a Function without Jest

Starter project

Manually