Jest is a highly regarded testing framework that complements Selenium test execution capabilities. With its impressive developer satisfaction, interest, and awareness, Jest stands out as a preferred choice.  

It offers a comprehensive library that not only identifies areas of code failure but also provides coverage analysis to understand the impact of code changes on tests—an invaluable feature. Previously, when making alterations to a codebase, uncertainty often arose regarding the affected sections. Jest eliminates this ambiguity by instilling confidence. 

Jest is packed with robust testing capabilities, and its user-friendly API simplifies the process of writing unit tests. While initially designed by the Facebook team for testing React applications, it extends its capabilities beyond React. It caters to all forms of JavaScript testing, including browser tests. Jest’s versatility and functionality make it a suitable choice for a wide range of testing requirements. 


What is Jest? 

 Jest is a popular JavaScript testing framework that enjoys widespread adoption and is actively maintained by Facebook, Inc. It provides comprehensive testing capabilities for a variety of front-end projects, supporting technologies such as Babel, TypeScript, Node.js, React, Angular, Vue, and many others. 

Initially created to cater to Facebook’s chat functionality, Jest is coded in JavaScript and has since expanded its functionality to encompass a wide range of core features, making it a versatile and robust choice for testing needs.


Why should you choose Jest for Selenium JavaScript testing?  

Well, there are several compelling reasons that make Jest stand out from other test frameworks. Here are some key points that highlight the advantages of using Jest: 

  • Jest offers speedy test execution, with the selective running of changed test cases in watch mode. 
  • It provides pre-commit hooks for executing relevant tests, streamlining the process. Jest comes with essential features and built-in modules, avoiding the need for third-party tools.  
  • Migrating to Jest is effortless with the code mods module. 
  • It offers advanced features like automatic mocking, coverage thresholds, module mappers, and multi-project support. Jest also allows customizable resolvers for personalized configurations. 


Mistakes to Avoid in Selenium Jest Automation Testing 


1.Including network calls within tests 


When investigating the causes of slow and unreliable tests, it was discovered that API calls were being made directly inside the React components for testing purposes. This sparked curiosity, and it turned out to be true. The test cases relied on API responses, leading to slower execution. 

Ideally, unit tests should produce consistent results every time they are run. However, when network dependencies are involved, achieving this becomes impossible. 

To address this issue, the team came across a solution called jest-offline. By implementing this tool, the team could identify the test cases that made API calls and manually mock those calls. Although this process took some time, it proved to be worthwhile. 

With jest-offline in place, a new rule was enforced: failing the test if any calls were not properly mocked. This approach ensures that tests are not reliant on actual network requests and maintains the integrity and stability of the test suite. 


2.Optimizing unnecessary operations and wrappers 

  • Cleanup Unnecessary I/O Operations: Avoid unnecessary I/O operations, such as accessing LocalStorage, that can impact test performance. 
  • Unmocked Timers in Test Cases: Ensure that timers are properly mocked in your test cases to prevent delays or unexpected behaviors. 
  • Unnecessary Wrappers for Components: Evaluate if certain wrappers, like Sentry for error tracking or Analytics for data collection, are necessary for unit testing purposes. Removing them can streamline your tests. 
  • Sentry Wrapper: For unit testing, the Sentry wrapper, used for error tracking, is not required. 
  • Analytics Wrapper: Similarly, the Analytics wrapper, used for data tracking, is not necessary for unit testing. 


By being mindful of these factors and optimizing unnecessary operations and wrappers, you can further enhance the efficiency and speed of your unit tests. 


3.Failure to consider cross-browser compatibility  

This can lead to issues and inconsistencies when users access your application from different platforms and browsers. It is essential to include cross-browser testing in your test strategy to ensure optimal compatibility and usability across a wide range of browsers. 

Each browser has its own rendering engine, JavaScript interpreter, and CSS support, which can result in variations in how web pages are displayed and function.  

LambdaTest is a cloud-based digital experience testing specifically designed for web and mobile app testing, offering a wide range of real browsers for both manual and Selenium automation testing. With over 3,000+ browsers available, LambdaTest provides an extensive platform to ensure your application functions seamlessly across different browser environments. 

Jest, as a standalone framework, does not natively support parallel execution of tests. However, with LambdaTest, you have the capability to run concurrent test sessions. This means that different Jest scripts can be executed simultaneously on multiple browsers. By leveraging concurrent sessions, you can significantly reduce the overall test execution time compared to running tests sequentially. 


4.Switch to improve performance by upgrading to Jest version 28  

This update brought numerous performance enhancements to our testing process. Similarly, we also upgraded to NodeJS version 16, which further contributed to improved performance. These changes had a significant positive impact on the overall speed and efficiency of our testing. 

In addition to upgrading Jest, also make a parallel upgrade to NodeJS version by migrating to the latest NodeJS release, you can leverage the performance optimizations and improvements introduced in the newer version. NodeJS 16 introduced various enhancements, including improved garbage collection, enhanced performance metrics, and an updated V8 engine, all of which contribute to overall performance. 


5.Address the slowest test case 

Identifying these slow tests is the initial step in the optimization journey. It’s possible that a handful of slow tests might be consuming a significant portion, such as 80%, of the overall execution time. Therefore, it’s important to identify and address these bottlenecks. 

To identify the slowest tests, we can utilize a tool called jest-slow-test-reporter. This tool provides insights into the execution times of individual tests, allowing us to pinpoint the slowest ones. Once you have identified the slow tests, you can focus on improving their performance. 


6.Memory leaks 

It can be a significant factor in slow and unreliable tests. However, they are often overlooked in the testing process. It is crucial to proactively identify and address the tests that are causing memory leaks. 

To tackle this issue, it is recommended to take proactive measures to identify the tests that are causing memory leaks. By monitoring the memory usage during test execution, you can pinpoint the specific tests that are consuming excessive memory or not releasing resources properly. 

Identifying these memory leak culprits is an essential step toward improving the overall performance and reliability of your test suite. Once identified, you can focus on fixing the memory leaks in those specific tests and ensuring that resources are properly managed and released. This will result in more stable and efficient tests, reducing the likelihood of slowdowns or test failures due to memory-related issues. 


7.Review of test cases especially when using the React Testing Library 

One common factor that can contribute to slow tests is the use of incorrect selectors. Identifying and addressing these issues can significantly improve the performance of your tests. 

One particular concern is the excessive use of the .type method. It’s important to utilize this method only where necessary. In cases where it’s not required, consider using the .paste method instead. This alternative method is generally faster, leading to improved test execution times. 

By reviewing and optimizing the use of selectors in your test cases, you can avoid unnecessary delays and improve the overall performance of your tests. This optimization step is crucial for ensuring efficient and reliable testing processes. 


8.By utilizing the findRelatedTests feature 

You can significantly reduce the test execution time. This flag ensures that only the tests related to the specific code changes you’ve made are run. Instead of executing a large number of tests, this approach allows you to selectively run a smaller set of tests that are relevant to the 20 files you’ve modified. Consequently, the test suite execution is expedited, providing faster feedback on the impact of your code changes. 

Additionally, the –changedSince option can be employed to run tests associated with the alterations made since a specified branch or commit hash. This feature further refines the selection of relevant tests based on recent changes. By running tests specifically related to recent modifications, you can focus testing efforts and reduce unnecessary test execution, ultimately optimizing the testing process. 

By utilizing these selective test execution options, you can save time and resources while still ensuring comprehensive test coverage for your code changes. This targeted approach enhances the efficiency and effectiveness of your testing workflow. 


9.Switching the test environment from JSDOM to an alternative like LinkeDOM 

This has the potential to significantly enhance performance, with twice the expected improvements. Exploring this option and evaluating its compatibility and effectiveness within your specific configuration is essential. 

Implementing LinkeDOM as an alternative test environment can offer performance benefits, but conducting thorough testing and assessing its compatibility with your existing setup is essential. By experimenting with LinkeDOM and monitoring its impact on performance and test execution, you can make an informed decision on whether to adopt it as a replacement for JSDOM. 

Keep in mind that while LinkeDOM shows potential for performance gains, it is essential to evaluate its compatibility, stability, consistency, and reliability within your specific testing environment. Consider running a series of tests and gathering metrics to accurately gauge its impact. This approach will allow you to make an informed decision based on your specific needs and circumstances. 


10.Poor test case design 

Writing test cases without proper planning and organization can result in inefficient and ineffective automation efforts. It is crucial to invest time and effort in planning and designing your test cases before implementing them. 

Proper test case design involves several key aspects. First, it’s essential to have a clear understanding of the application or feature under test. This includes identifying the various functionalities, user interactions, and expected outcomes. By thoroughly analyzing the requirements and specifications, you can ensure that your test cases cover all the necessary scenarios and edge cases. 

Next, consider the structure and organization of your test cases. Categorize them based on specific functionalities or features to ensure clarity and maintainability. This allows for easier identification and tracking of test coverage. Establish a naming convention that provides meaningful and descriptive names for each test case, aiding in better comprehension and maintenance. 



When we combine the powerful features of Selenium and Jest, we create a highly effective and efficient testing environment. Each tool brings unique capabilities to the table, making them a perfect match for different aspects of the testing process. 

Jest provides a robust and intuitive API, making it straightforward to write and execute unit tests for JavaScript applications. Jest offers features like test isolation, assertions, and code coverage, allowing developers to ensure the quality and reliability of their code. 

By implementing these solutions, you can streamline the test environment setup process and improve the reliability and consistency of your Jest Selenium automation testing, ultimately enhancing the efficiency and effectiveness of your testing efforts. 

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