An Overview of JavaScript Testing in 2019

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An Overview of JavaScript Testing in 2019

With access to various resources, it has become easier as well as entertaining for the testers to test web apps — including JavaScript.

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The web has evolved a lot in the last few years, and we have observed this evolution with our eyes. From having limited programming languages to getting access to a hub of languages for testing, the web has come a long way.

Just a few years ago, the web app testing used to be slow, costly, complicated and was not fun at all for the testers. With access to various resources, it has become easier as well as entertaining for the testers to test web apps. And one language that has evolved with the web is JavaScript.

You may also like: JavaScript Testing and Debugging Tools

JavaScript is not only great for software developers, but testers are also happy with the process of JavaScript testing. Today, we have access to practical web app testing tools like LambdaTest, which is fast, informative, easy to use, which makes the testing and developing experience entertaining for us.

Another thing that has entered into the web app testing field in reference to AI is automation, which is making JavaScript testing more flexible and fun. There are multiple automation testing tools available in the market for JavaScript testing.

This article is written to provide you with the most important analysis, relations, tools, and techniques for JavaScript testing in 2019. Let’s have a look at the different aspects of JavaScript testing for 2019.

1. Types of Tests in JavaScript Testing

Every programming language involves different types of tests, and JavaScript is no different than other languages. There are various test types involved in JavaScript, the most important test types for a web app are:

Unit Tests

It involves testing individual units of a web app like functions, classes, etc. by providing the input and ensuring the output as expected:


Integration Tests

It is performed across specific units of a web app to achieve their primary goals, including side errors:



const flyDroneButton = document.getElementById('fly-drone-button')
//or even
.then(isFlying => assert(isFlying))

Functional Tests

Also known as the End-to-End test, it is executed to verify the functionality of a web app. It analyzes how web app elements perform on different platforms. The internal structure of the web app is not involved in end-to-end testing, as it is a type of black-box testing. We will discuss functional testing in detail at the end of the article.


2. Running the Tests

Running tests for JavaScript is not that complicated, you can run the tests by generating an HTML page included with test libraries and tests as JS files.

You can also choose to execute tests in Node.js by importing the tests and conditional libraries. Usually, jsdom is used in Node.js for replicating a browser-like environment with JavaScript. With Node.js, you get access to window, location, document, selectors, body, cookies, and whatever you need to execute your JS inside the browser. In reality, none of that is real. Also, it is not similar to headless mode, as you need a real browser for a headless mode.

In our opinion, we believe the combination of Node.js + jsdom is a better option to run tests because it provides better performance and speed as compared to running tests in a real browser.

3. Test Tools for JavaScript Testing

Every testing process requires testing tools to make the process faster and easier for the testers. However, there is not a single tool that can be used for JavaScript testing, it can be divided into multiple functionalities. Some of these tools provide us with one functionality; some offer a combination of functionalities.

Below, we have mentioned a combination of tools that you can use in different scenarios to achieve the desired functionality.

Test Launchers

Test launching tools are provided with a list of tests, which require various configuration and frameworks, such as browsers to run in, how to format output, plugins to use, etc. to run.

To launch your tests either in the browser or Node.js, you need user config with CLI or UI. It can also be achieved manually with tools like Karma, Jest, TestCafe, Jest.


Testing Structure

The testing structure is a collection of standardized tests that are usually arranged in a BDD structure, which supports behavior-driven development (BDD). An example of the test structure is given below:



describe('calculator', function() {
// describes a module with nested "describe" functions
describe('add', function() {
// specify the expected behavior
it('should add 2 numbers', function() {
//Use assertion functions to test the expected behavior

To arrange your test files in the testing structure, you can use Mocha, Jest, Cucumber, Jasmine, LambdaTest.

Assertion Functions

These functions help testers ensure that the tested variables encompass the expected value. Check out the below code to have a look at it:



// Chai expect (popular)
// Jasmine expect (popular)
// Chai assert
assert.typeOf(foo, 'string')
assert.equal(foo, 'bar')
// Unexpected expect
expect(foo, 'to be a', 'string')
expect(foo, 'to be', 'bar')

To ensure that executing tests return the same output as expected, use Chai, Jasmine, TestCafe.

Generate and Display Test Results

For generating and showing test progress and results, use Mocha, Jest, Jasmine, TestCafe.

Generate and Compare Screenshots

Screenshot testing is executed to analyze the data structures with the expected results. Here is an example from Jest documentation that displays a snapshot test of a particular link component.

To generate and compare screenshots of web pages to ensure changes from previous runs are implemented, use Jest, Ava. Generally, screenshots are created to analyze representation data, but they can also be used for examining other data types, such as the internal structure of different units in an application.

Browser Controllers

Browser behavior can be regulated with the help of drivers that are available within the browser. For example, you can use Selenium to control a browser behavior or with a script injection of a JS code that gives access to the entire application environment, such as DOM, cookies, network, etc.

To ensure functional testing of web apps across various browsers, use Selenium, TestNG, LambdaTest.

Creating Code Coverage

To generate code coverage reports for analyzing how much code is covered by tests, you can use Istanbul, Blanket, Jest.

Visual Regression Tools

Use visual regression tools like Wraith, LambdaTest, WebDriverCSS to compare your site to its previous versions with image compression techniques.

4. Keeping It All Together for Javascript Testing

We have discussed the components of JavaScript testing, now let’s put it all together to describe how to execute JavaScript testing.

Depending upon the above points, you can choose to begin with testing structure, assertion functions library, and decide how to execute tests. If you choose to run the tests with the frameworks, then some of them provide all these functionalities, such as Jest, Jasmine. Whereas, some tools only offer limited functionalities and libraries, such as chai, mocha, etc.

We believe, testers should have two different approaches for JavaScript testing – one should be focused on unit and integration tests, and another on functional testing. This is because functional testing is often complicated to execute, especially while running tests on different browsers.

5. Unit Testing and Integration Testing

While executing unit tests, you must every cover every unit of the application with simple and edge case inputs, and ensure that their outputs come as expected with the assertion function.

Earlier, most web app testing was focused on unit tests, which often resulted in the failure of web app working as a whole. Integration tests help in identifying the causes that are not factored by unit tests and then execute tests for those units.

6. Frameworks for Unit Testing and Integration Testing

The first thing that you need to execute unit and integration tests is a testing framework. Also, depending on the framework you use, it is advisable to use the tools that are available with the framework unless an external tool is required.

Let’s have a look at the most prominent Unit and Integration testing frameworks.


Jest is amongst one of the best testing frameworks for Unit and Integration testing; it is developed and maintained by Facebook with broad community support. Though it is based on Jasmine, most of its functionality and features are replaced by Facebook. It is included with various features, such as:

  • Speed — It is the first choice of testers for big projects that consist of multiple test files because it is integrated with a parallel testing mechanism.

  • Ready-to-go — It is included with mocks, assertions, spies that are similar to libraries like Sinon. However, you are still allowed to use libraries if required.

  • User Interface — Comes with a friendly and straightforward interface, which makes it easy to use for testers.

  • Enhanced Modules Mocking — It offers an easy way to mock heavy modules to enhance the testing speed.

  • Snapshot Testing — The snapshot testing feature can be used as a part of the framework integration with other frameworks as well.

  • Reliability  From the last two years, Jest has been recognized as a trusted and reliable framework.


Jasmine has been around the corner for a long time. In fact, the Jest framework is also based on this amazing framework. The reason we are mentioning Jasmine is that there are multiple articles, forums comments answered by trusted communities. Also, it provides some valuable features for Unit testing, such as:

  • Globals – It gives the essential testing features in the global scope.

  • Angular – It comes with massive Angular support for all its versions.

  • Ready-to-go – Consists of everything that you need to run your JavaScript testing.

  • Community – Have community support since its launch in 2009 with a variety of articles, forums, suggestions, tips that are entirely based on it.


Mocha is a library-based framework, which is used with third-party mocking, assertions, and spying tools like Chai. Also, it is a bit complicated to set up the framework and divide it into multiple libraries, but as compared to other frameworks, it is highly flexible and open to all extensions. The features offered by Mocha are as follows:

  • Extensibility – Mocha is extremely extensible to the point where you can run uniquely designed extensions, plugins, and libraries on top of it.

  • Community – Just like Jasmine, Mocha also has multiple plugins and extensions to run unique test scenarios.

  • Globals – By default, the test structure globals are automatically created in Mocha.

7. Functional Testing

As a tester, you might be aware of the fact that unit tests and integration tests are not enough to analyze the overall performance of a web app. That’s why it’s crucial to execute functional tests for a web app. Functional testing guarantees that a website is working as expected from an end-user point of view.

With functional testing, some other tests are also executed that ensures the browser compatibility of web apps on different platforms, such as visual regression testing, which is performed to test different screen resolutions of a web app. It is executed by comparing the screenshots of the web app that are taken as a part of functional testing.

8. Functional Testing Tools

When it comes to functional testing, there are a variety of tools available in the market, and the purpose of each is different than others in terms of implementation, API, philosophy. So, it is recommended to invest some good time in research before finalizing a functional testing tool. For instance, if you want to get started with a simple set up process and easy to use the tool, then LambdaTest is the ideal choice for it. Although there are other functional testing tools available, such as:


Selenium is ruling the market when it comes to choosing a functional testing tool because it can control a browser for various purposes with the browser drivers and extensions. Selenium is not just a single entity, it consists of four different tools – Selenium Grid, Selenium IDE, Selenium WebDriver, and Selenium RC.

Amongst which, Selenium WebDriver is widely used because you can access in multiple ways with various programming languages. And some tools allow you to use WebDriver without any additional programming.

You can easily import WebDriver into any testing framework, and then write the scripts as a part of it. Consider the below code for example:

If you are entirely familiar with WebDriver, then you would stick to it for functional testing, but some users prefer to use it directly because it makes debugging harder. So, they go for other functional testing tools mentioned below:


WebDriverIO uses its own implementation of Selenium WebDriver to execute functional testing. It is almost similar to WebDriver and provides excellent flexibility to the users.

The syntax of the WebDriverIO is easy to read and understand, as well as it comes with an extensible library, which makes it more popular amongst developers. Also, there is an excellent developer community behind it that offers continuous support to the users.


Nightwatch is also known for having its own implementations of selenium WebDriver while having its own test driver, testing framework, proclamations, and tools. Moreover, you can integrate it with other testing frameworks as well, but that’s only helpful if you are not interested in executing functional tests as part of another framework.

The syntax of Nightwatch is easy to read and implement. But, there is not a great support community behind this framework, which makes it less popular.


For those who are not comfortable using Selenium-based tools can opt for TestCafe, which become an open-source testing tool at the end of 2016.

Selenium controls the behavior of a browser, whereas, TestCafe injects itself as JavaScript scripts in the web app, which enables it to run on any browser, including mobile devices. It is also available with a paid subscription that provides non-programming testing tools, which will be replaced by TestCafe Studio soon.

TestCafe can be set up quickly on any system by installing NPM to run your first test on any browser. And if you want to run tests in parallel, then TestCafe allows you to run your tests on multiple browser instances at once.


Well, LambdaTest is not just a functional testing tool. It is a testing suite that is included with all the features and functionalities that you need for JavaScript testing. For instance, if you want to automate the cross-browser compatibility testing for your web app, then LambdaTest is the ideal choice for you because it offers a combination of more than 2000 browsers, operating systems, and devices to test your web app.

Moreover, if you are willing to perform real-time or parallel testing for your web app, then that can also be executed efficiently. LambdaTest is not just helpful in terms of automation testing but also in manual testing, as it allows users to perform responsive and visual regression testing for their web apps.

LambdaTest is compatible with almost every programming language, including JavaScript, Java, Ruby, C++, Python, etc. With the help of features like Screenshot API, WordPress Plugin, and Chrome Extension, you can make your web app testing faster and secure.

9. Visual Regression Testing

Though visual regression testing can also be performed with the same tools of functional testing, there are some tools that are specially designed for it, which consists of the following things:

  • Screenshot feature for providing images or DOM snapshots of web pages.

  • Techniques that can be used to automate the testing process as a part of functional testing.

  • Features to compare DOM and images to analyze the differences.

There are various tools that offer these features and functionalities, such as Percy, Happo, BackstopJS, etc.

Though these tools require some coding to run your tests, there are tools that don’t involve any coding for running functional tests, such as:

  • Testin – Enable you to open your app in a separate window and records your interaction with the application using a browser extension.

  • Screener – This tool allows you to record your tests with a Chrome Extension with in-depth visual regression reporting.

You can also access these features with LambdaTest, as mentioned above. So, you can decide which JavaScript testing tool is ideal for you.


JavaScript has become widely popular amongst developers for developing amazing apps and sites, which makes it crucial for testers to have complete knowledge of JavaScript testing because a web app is never secure or reliable until it is thoroughly tested.

With that in mind, we tried to give you an overview of JavaScript testing. From executing unit tests to automating cross-browser testing, we covered almost everything related to JavaScript testing, including the tools and frameworks that can be used for it.

Further Reading

Top Eight JavaScript Automation Testing Frameworks In 2019

How to Test JavaScript Code in a Browser

How to Practice Your JavaScript, Software Testing, and Test Automation Skills

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