How to Debug Cross Browser Tests with Jest?

by Adnan Mujic
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Cross Browser Testing has grown to become an essential part of any application or website’s development. With the rise in the number of web browsers and their separate user bases, the importance of ensuring your website works on any web browser has increased drastically. It is so because not only is it essential for ensuring their browser compatibility but also to see if the functions embedded in their source code work and degrade as intended.

Although testing the entirety of web applications on multiple browsers manually is an exhausting task. Fortunately, testing frameworks like Jest enable conducting cross browser tests efficiently and effectively with the least time period possible. Moreover, this JavaScript open-source framework allows more than just writing cross browser tests, as its varying features also enable its users to debug their tests, which is as important as drafting the entire tests.

However, the process of embedding and running your code on the framework for the first time can be confusing. So, to put an end to this struggle, here is a thorough guide on how to debug your cross-browser tests using Jest.


What is Jest Framework?

Jest is among the most known names among the testing frameworks that allow for effective unit testing and cross browser testing. It is a JavaScript open-source framework that best works with react-native-based web applications to conduct testing.

But if it is just like every other testing framework, then how is it unique? Well, Jest:

  • Specializes in the creation of automated browser tests with its blended package of built-in mocking library, test runner, and an assertion library.
  • Hosts a user-friendly and feature-rich Application Programmable Interface (API), making it a greater option than others to write and debug tests.
  • Is a framework in itself and not a library. Hence, it is independent and can function without any reliance on third-party tools.

Features That Set Jest Apart from Its Competition

Jest is a highly efficient framework for creating tests, be it unit tests or cross browser tests. Created by Facebook initially, its features are all designed to be user-centric. Some of them are as follows:

  1. Snapshot Testing: Tracking changes in the working of any web application’s UI is essential, and this feature allows for it. It captures a component’s code at a specific time and keeps it alongside the test’s reference snapshot to track their differences.
  2. Interactive Mode: Git and Mercurial integrate with Jest, which is a normal perk. But Jest makes the feature unique by making only the changes-affected tests run, thereby allowing users to make more atomic commits.
  3. Easy Set Up: Just after installing Jest, the framework is good to run and use without first installing any additional plugins or libraries unless specifically required.
  4. VS Code extension: VS Code is among the most famous Integrated Development Environments, used by over 73% of developers worldwide. To make it a great environment for testing as well, Jest offers an efficient extension for VS Code.

Thus, Jest is undoubtedly one of the leading quality testing frameworks out there, and for good reasons.

You can now execute Jest automation testing using the LambdaTest platform – which is SOC2 Type2 certified and fully GDPR compliant. It is backed by over 2 million developers in 130+ countries and lets you run tests on reliable, scalable, and secure cloud-based infrastructure with instant on-demand access to 3000+ desktop and mobile browser environments.

How to Install Jest for Cross Browser Testing?

Jest is a full-fledged framework that doesn’t require downloading any libraries after the framework’s installation. However, the framework requires some prerequisites, including Libraries and Packages predefined to check specific test scripts installed in the computer beforehand.

The aforementioned prerequisites include:

  • Selenium Web Driver:It is the web framework that allows the user to utilize any programming language and create test scripts for Cross Browser Testing. Such an important ability of this driver makes Jest rely on it.

To download it on your PC, you can use the following command line:

$ npm install selenium-web driver,

Or use this command to install Jest using npm:

$ npm install –save-dev Jest.

  • Node Package Manager and NodeJS:NPM is the open-source software library that consists of numerous code packages, approximately 8 lakhs+, used for updating, installing, and uninstalling NodeJS-related packages in mobile or web-based apps. NodeJS, on the other hand, can be installed using the Windows Installer Binary with npm or the org website.

To initialize the installation of npm, all you need to do is apply this command:

$ npm init -y.

Ways to Setup for Cross Browser Testing

Web applications are complex structures and comprise a notable level of functions and modules that all need to go through Cross Browser Testing. These applications are the result of a bundle of units of codes that form all their modules and functions. Thus, to test the overall performance of any application, all these modules and functions need to be tested, which is done by the test of their codes.

To conduct each required test, following the predefined flow is essential. The said flow goes as follows:

  1. Importe the particular function for the required test
  2. Implement the necessary input
  3. Specify the function’s goal to produce the desired output
  4. Check whether or not the function is aptly working.

How to Debug Cross Browser Tests with Jest?

Jest tests are based on identifying what bugs exist in the already written code, which can potentially prevent the document from aptly working in various browsers. Though so, the test written to conduct the required automation testing of the source code often requires debugging in itself. The first resort to check for the required bugs and debug them is to use console.log. But sometimes, this option fails as it prints only plain objects when there are additional elements of objects and circular references as well.

Thus, to debug the required Jest script, there are three options that can produce the required result, all of which work as extensions in the VS Code. Being the most efficient IDE that offers the installation of the Jest extension, conducting Jest debugging in it with the help of additional breakpoints and statements.

To state there are three ways of debugging Jest tests:

  1. Using the In-Built Debugger

VS Code is a well-versed IDE and comprises an in-built debugging support feature for the runtime of Node.js. This feature enables the user to debug code written in any language by transpiling it into JavaScript. The steps to enable the debugger are:

  • Open the .vscode Folder
  • Locate the launch.json file and open it
  • Add the following input to it:


“version”: “1.0.0”,

“configurations”: [


“type”: “node”,

“request”: “launch”,

“name”: “Jest: current file”,

//”env”: { “NODE_ENV”: “test” },

“program”: “${workspaceFolder}/node_modules/.bin/jest”,

“args”: [“${fileBasenameNoExtension}”, “–config”, “jest.config.js”],

“console”: “integratedTerminal”,

“disableOptimisticBPs”: true,

“windows”: {

“program”: “${workspaceFolder}/node_modules/jest/bin/jest”






  • Open the cross browser test file that requires debugging.
  • Put the brakepoints/debugger statement on the point where you want to stop the test.
  • Click on the Debug icon located on the left panel, or press Ctrl+Shift+D.
  • Press on the Jest: Current File option open on the top panel.
  • Click on F5, and the debugging will start.
  1. Using the Node Environment’s Built-In Debugger

The Jest runs under the preset of the Node Environment in VS Code. Thus, its in-built debugger is helpful for connecting an external debugger and opening up the required process to run the cross browser test.

Thus, run the command:

  •        node –inspect-brk <node-args> <jest-cli-path> <jest-args>.

In case you have previously installed jest-cli in package.json, then you should run the command:

  •        node –nolazy –inspect-brk ./node_modules/jest-cli/bin/jest.js –runInBand –colors –verbose <path/to/file>.

Lastly, if you have Jest previously downloaded in your system, you can just change the path of the executable with the command:

  •        node –nolazy –inspect-brk ./node_modules/jest/bin/jest.js –runInBand –colors –verbose <path/to/file>.
  1. Using Chrome Debugger

In case the VS Code extension fails you in any way, you can use the previously stated command and register in package.json to run the Jest Debugger as an npm script with the command

  •        “jest:debug”: “node –nolazy –inspect-brk ./node_modules/jest/bin/jest.js –runInBand –colors –verbose”

Then, open Google Chrome or any related Chromium-base browser, and to debug the Jest, follow the given steps:

  • Embed the debugger statement in your test files.
  • Run the compilation command: npm run Jest:debug path/to/file
  • Then type chrome://sinpect,
  • And press on Open Dedicated DevTools for Node/ Select the Remote Target that you can connect with.
  • (Afterward, Chrome DevTools will start, and the code execution will pause.)
  • Click on the Resume Script Execution button.

With these methods, you will be able to debug your opted test and move on to conduct apt Cross Browser Testing, required to make the intended website fit for working on any required browsing platform.

How Important is Cross Browser Testing?

Cross Browser Testing holds an irreplaceable place in the quality testing world now. With more and more competition in the market, creating the best website and ensuring it works perfectly, despite the platform it is used in. Not going through the phase of Cross Browser Testing makes applications glitch through various platforms. Moreover, it makes all the functions and features programmed with time and effort go in vain and reduces the potential of your website application.

Such a phenomenon occurs because even though all the browser vendors follow the Open Web Standards to make their own distinct effects, they all interpret the OWS in their own ways. Thus, with every one of them rendering HTML, CSS, and JS differently, web browsers often interpret various codes and features differently and behave accordingly. Therefore, Cross Browser Testing contributes to pointing out the elements that are acting differently in different browsers and debugging the differences efficiently.


How to Select the Right Browsers for Cross Browser Testing?

Cross Browser Testing includes testing between some of the leading browsers only, as checking in the sheer number of varying browsers, devices, and operating systems present online is impossible. Therefore, it is more productive and realistic to conduct Cross Browser Testing among the leading browsing platforms. To choose such browsers, the best rule of hand is to consider these two elements:

  1. Popularity: Observe the 10-20 most popular browsers used in the most common operating systems, i.e., Android and iOS, and optimize the website for use in these.
  2. Targeted Audience: It is essential to include the browser preferences of the targeted audience of any web application.

Also, a great rule of thumb is to always consider the browsers that cover more than 5% of online traffic.


Cross Browser Testing is essential to conduct during the development of the pre-release stage of any web application. Jest makes conducting it notably efficient with its exemplary features and user-friendly UI. Furthermore, its VS Code extension minimizes user efforts and maximizes productivity while debugging the required cross-browsing tests. Therefore, debugging cross browser tests using Jest is an exemplary way of gaining the best results with minimal effort.


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