Tutorials: Create React App tutorial

Wallaby.js runs your JavaScript tests immediately as you type and displays execution results in your code editor. Wallaby also provides beautiful test and code coverage reports updated in realtime.

In this tutorial we’re going to share how to configure Wallaby.js using create-react-app. We’ve structured this tutorial so you can follow along. If you don’t want to follow along then you may skip ahead and find the end result in this github repo.

Select your editor

The content of this page is adjusted based on your editor of choice. Please select your editor by clicking on your editor’s logo below before proceeding:

Install Dependencies

First, if you haven’t done so already, go ahead and download and install Wallaby.js.

Create a new React App

Now that we’re ready to start, open your terminal and change directory to where we will create our new react app. Run the following command:

npx create-react-app wallaby-create-react-app

At this point, the create-react-app tool has created a new folder for us named wallaby-create-react-app with our base application.

Start Wallaby.js

After Wallaby.js has started, navigate to your application and test files (App.js, App.test.js), you will see coverage indicators in the gutter of your code editor:

• Gray squares mean that the line contains code that was not run by any of your tests.
• Green squares mean that the line contains code that was run by at least one of your tests.
• Yellow squares mean that the line contains code that was only partially covered by your tests.
• Red squares mean that the line is the source of an error, a failed assertion, or is part of a stack trace for an error.
• Pink squares mean that the source line is on the execution path of a failing test.

Open up App.test.js to confirm that everything is working. It should look like this:

Write a test for the expected output

Let’s update App.test.js to perform a jest snapshot for the div output, by changing its content to:

import React from 'react';
 import ReactDOM from 'react-dom';
 import App from './App';

 it('renders without crashing', () => {
   const div = document.createElement('div');
   ReactDOM.render(<App />, div);

   expect(div).toMatchSnapshot() /* This is our snapshot */

   ReactDOM.unmountComponentAtNode(div);
 });

When Wallaby.js is running (as it should be now), a new snapshot is automatically created when you use jest’s toMatchSnapshot() method.

Breaking a test

Let’s break the snapshot test that we just created and see what happens. Go ahead and edit App.js hyperlink text and change it from Learn React to Learn React with Wallaby.js.

You’ll see the line marker in App.js has changed to pink, and your Wallaby.js Test output window shows you that the render function no longer matches the snapshot.

At this point, you might like to Toggle Wallaby’s Panel by launching the Command Palette and selecting Wallaby.js: Toggle Tests View.

Update our snapshot

After reviewing the difference in our snapshot, we’re happy with the change and we want to update our snapshot. Let’s do that.

Update the snapshot using Wallaby.js by launching your Command Palette and selecting the command Wallaby.js: Update Test Snapshots, or by using the link in the Wallaby Failing Tests Output Channel.

Update the snapshot using Wallaby.js by launching your Command Palette and selecting the command Wallaby.js: Run line tests.

Update the snapshot using Wallaby.js by launching Visual Studio quick actions (Ctrl+.) and select Update Test Snapshots.

Update the snapshot using Wallaby.js by launching JetBrains Intention Actions (Alt+Enter) and select Update Test Snapshots, or by using the link in the Wallaby Failing Tests Console.

Using different commands you may update a snapshot for a specific test, a test file, or all snapshots for your project.

You’ll see that the error has gone away, and our tests are passing again.

You’re now ready to use Wallaby to write your create react app tests. With Wallaby, you still write your tests the same way that you do today but now you get real-time in-editor feedback.

Debugging a test

Wallaby’s Time Travel Debugger allows you to move forward and backwards through your code to understand the conditions that led to a specific bug. The Time Travel Debugger accelerates your edit, compile and debug loop by allowing you to jump to a specific line of code, view runtime values, edit-and-continue and step into, over and out of your code.

Wallaby’s Time Travel Debugger allows you to move forward and backwards through your code to understand the conditions that led to a specific bug. The Time Travel Debugger accelerates your edit, compile and debug loop by allowing you to jump to a specific line of code, view runtime values, edit-and-continue and step into, over and out of your code.

Once Wallaby has started, the time-travel debugger is available at any time. The debugger can be started from any of your project’s tests. Navigate to the line of code where your test starts and run the command, Wallaby.js: Debug Test (Shift + F5).

In addition to being able to start the debugger on the line of code where your test starts, you may also start the debugger on any line of your code that is executed by your tests. When you start the debugger from a line other than the start of your test, the debugger will start and automatically progress to that line. If you start the debugger from a line of code that is covered by multiple tests, you will be prompted to select which test you want to debug.

Wallaby’s Test Story Viewer provides a unique and highly efficient way of debugging your code and inspecting what code your test is executing in a single logical view. The view is integrated with Wallaby’s Time Travel Debugger and Value Explorer.

Learn More…

We’ve only covered the very basics of configuring and using Wallaby.js but the tool is capable of a whole lot more. Read through our docs to learn more about Wallaby.js features. Some notable features include:

• Wallaby App updates in real-time and provides a strategic level view of coverage and test results.
• Advanced Logging allows you to quickly and easily debug at runtime with keyboard shortcuts, comments, and console log.
• Value Explorer provides the ability to explore runtime values right in your editor.

You may also learn about more Wallaby features in the VS Code tutorialJetBrains IDEs tutorialVisual Studio tutorialSublime Text tutorial.

Troubleshooting

If you get stuck or something isn’t working for you, you may find a similar solved issue in our github issues repository. If you can’t find a solution, create a new issue.