Jest Testing Framework: Do’s and Don’ts

Jest Testing Framework
Jest Testing Framework

Jest stands out to be a champion among all JavaScript testing frameworks. It was created in 2011 when Facebook was rewriting its chat feature in JavaScript. It has been used on almost 4 million public repositories on GitHub as it is compatible with Angular, Babel, Node, React, TypeScript, and Vue. Facebook primarily designed it to ensure the correctness of any JavaScript codebase.   

The Jest framework permits writing tests with an amicable, familiar, and feature-packed API (Application Programming Interface) to generate swift results. Jest effectively matches your requirements as it is well-documented and requires minimal configuration. 

Jest saw more than 50 million downloads in mid-2022. It was crafted to execute unit testing for React components and became immensely popular quickly. Today, it is widely used to perform unit testing for React components and complete front- and back-end JavaScript applications. However, some people still misinterpret Jest as a library instead of a framework. Jest testing framework allows running relevant commands from the terminal as it incorporates a text-based command-line interface (CLI). 

What is Jest?

Jest testing framework is renowned for its delightful JavaScript testing. Based on Jasmine, a behavior-driven development framework, Jest was designed to perform unit testing of React and its native applications. The pioneer of Jest, Christoph Nakazawa says that its primary aim is to deliver support and simplicity in testing complicated web applications.  

Unit testing is not very useful on the front end of software. It increases complexity as it is wide-ranging and time-consuming. Jest adds simplicity to unit testing. Moreover, it aids in validating everything developed by using JavaScript and browser rendering of both mobile and web applications. Jest also plays a significant role in automated browser testing. Its popularity among other JavaScript testing frameworks is undisputable, and its simplicity makes it a unique framework for testing and developing several JavaScript library projects.

Apart from unit testing, Jest is also capable of testing different components of an application. It can be deployed to test each application component created using JavaScript, be it web or mobile. Jest’s non-reliance on third-party tools and applications gives it an edge over other testing frameworks. Jest testing framework gained immense popularity due to its ability to perform tests for both front- and back-end JavaScript applications. Soon, large companies like Meta, Twitter, Pinterest, Airbnb, Spotify, etc., started relying on Jest for react testing.  

You can effectively optimize the use of Jest in cloud-based digital experience testing platforms like LambdaTest. LambdaTest’s integration with popular test automation frameworks like Jest makes it a versatile and valuable tool for software testing teams. You can enable teams to easily execute automation tests as it supports Selenium Grid online and ensures their development code renders seamlessly across various browsers and operating systems.  

Do’s of Jest Testing Framework  

To successfully install and run Jest scripts on a system, it is crucial to have these libraries and packages installed: 

JDK (Java Development Kit):  Java is widely used to develop Selenium automation testing scripts. JDK 7.0 and above installation is mandatory as the Jest testing framework uses Selenium. 

NodeJS and NPM: Node JS can be installed from the Node Package Manager. 

Browser driver – A browser driver is vital in executing the protocols of Selenium WebDriver to convert commands into a browser-native API. 

Selenium WebDriver: Jest framework needs the Selenium WebDriver installed in the root directory of a system to test on a Selenium Grid. It can be installed after installing the NPM. 

Moreover, the Jest framework is compatible with all major browsers like Chrome, Firefox, Edge, Opera, and Safari. Once the setup and installation of Jest and its prerequisites are done, it is time to test with Jest. 

Although many JavaScript testing frameworks are competing with Jest in cross-browser testing, Jest has simply been the best – thanks to its advantages: 

  • Easy to Install: Jest testing framework is easy to set up on any operating system. It can be directly installed by using the library named NPM (node package manager) or Yarn. Its module can be installed globally using the ‘- g’ flag with the NPM command line. The ‘-g’ flag can use the Jest command without installing package files for npm tests. The numerous modules incorporated in the Jest package help initiate writing tests instantly. 
  • Speed and Performance: Jest testing framework is extremely quick in performing a test case, effectively and swiftly, without any delay, even on an average operating system. If a test is CPU-bound, Jest can save significant time from test runs. Tests that take more time are run first, and due to this, all cores are utilized to the maximum limit. Parallelization, a semi-automated testing feature in the Jest framework, allows the simultaneous execution of tests against various configurations. Moreover, it efficiently catches Babel conversions, although Babel is an open-source trans compiler of JavaScript. 
  • Isolated Execution of Tests: Each test in the Jest framework runs in its own sandbox. This guarantees that two tests cannot affect the working of one another. It ensures that a test running on Jest cannot interfere with the execution of another test. All tests execute in parallel systems. The primary idea behind the isolated running of tests is to create an environment in which each and every test runs one at a time. This avoids interference with the execution of other tests. This permits the Jest framework to run faster. 
  • Powerful Mocking: Mocking is powerful when used in the Jest testing framework. It separates the test subjects developers employ by interchanging the dependencies with objects. This makes it easy to inspect and control. Mocking in Jest testing is, in other words, the replacement of dependencies with mock functions. All kinds of mocking – API calls mocking, functional mocking, and timer mocking – are backed by the Jest testing framework. 
  • TypeScript Support: Server-side execution and client-side execution of JavaScript applications are developed using TypeScript. Jest testing supports TypeScript. It is employed using the ts-jest package. TypeScript uses simple JavaScript, which proves to be extremely beneficial. Also, it is a popular superset of JavaScript. With the backing of a source map for Jest testing, the ts-jest package is a TypeScript pre-processor. 
  • Snapshot Testing Support: Snapshot testing is a great feature as it captures a string representing any given component and stores it in a file. Although Snapshot testing is suitable for React applications, it is also used to compare the sequenced values of different frameworks. Snapshots of a React component help validate that particular component’s behavior. To change a UI (User Interface), it is important to update the Snapshot file. 
  • Inbuilt Code Coverage: Jest framework incorporates built-in support for codes. It provides creative CLI-based commands to ensure accurate code coverage and an application’s efficiency. It can be achieved by using the coverage command or the collectCoverage feature in the Jest configuration file.
  • Rich API: Jest testing framework entails various APIs that permit matching and validating values to extract desired conditions. For example, the Expect API incorporates several matcher functions that are used to confirm certain conditions and values. Jest users can easily add their matches to its API list as it is an open-source framework. 
  • Easy to Migrate: The jest-codemods module makes it easy to migrate to Jest without facing typical programmatic issues and doing any dirty migration work. Migration to Jest is flawless, be it from Chai, Jasmine, Mocha, or Tape. 

Don’ts of Jest Testing Framework 

Jest is indisputably the best JavaScript testing framework with several advantageous features in its kitty. However, Jest is not simple and speedy every time. Let’s have a look at some major don’ts while using the Jest testing framework, which comes in the form of a few limitations. 

  • The major drawback of Jest is that it is new. Therefore, it is still gaining recognition among JavaScript developers.  
  • A technology like Jest can be really helpful when a developer can execute and debug their tests in an IDE (Integrated Development Environment) like WebStorm. WebStorm never supported Jest tests till recently. Although the most recent WebStorm release saw some improvements, the debugger still fails to complete tests properly. This is a huge limitation for developers looking to debug and run their tests on WebStorm. 
  • Compared with mature libraries like Mocha, the Jest framework still needs enhanced library support and more tooling.  
  • Using automated mocking characteristics in the Jest testing framework usually slows testing. In cases where a module has more dependencies, Jest has to execute more work to ensure that they act like real dependencies while testing a code. 
  • For applications and projects creating large snapshot files with thousands of command lines, Snapshot testing with Jest is not an efficient match. 
  • Jest is not fully mature as it is new. Therefore, using Jest globally on huge projects requiring multiple testing techniques becomes very challenging. 


The Jest testing framework is convenient, efficient, and fast. It has a rich API and frequently used packages. It supports Typescript and Snapshot testing. A steep rise in its usage in recent years establishes that Jest is becoming a forerunner among the automation testing frameworks for JavaScript testing. 

However, the most important factors while selecting a JavaScript testing framework are the needs and expectations of a developer. Choose wisely! 



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