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The Importance of Parallel Testing in Selenium

Testing solutions have become more scalable with the advancement of technology, easing organizations’ move from manual testing to Selenium test automation. But nothing comes easy. Running multiple tests in parallel is still unscalable for many organizations. They tend to follow conventional, sequential testing methods to deliver A-Class quality assurance demanding high time, efforts, and resources. Organizations are either hesitant to implement parallel testing in Selenium or not adopting it because of their small-sized web applications that aren’t ready for parallel testing. But, somewhere down the line, web applications are bound to expand at every release. So adopting parallel testing will only save it from any obstacle in the long run. Testers should never forget that the Selenium Grid is only to allow them to run parallel test cases.

Let us understand the importance of parallel testing in Selenium and how it is going to help testers in their next release cycle.


Understanding the Concept


Before moving ahead, we must know what parallel testing means. In simple terms, it is a technique used to help testers run multiple tests concurrently across multiple devices or operating systems to reduce overall test execution time. When a test automation framework integrates with a cloud solution, it enables testers to scale multiple tests across platforms in parallel, smoothly. The main benefits of parallel testing are: 

  • It accelerates the test execution across different versions
  • Saves time at a greater level when testing at a larger scale
  • Increases test coverage by allowing testers to test across devices, OS, and browser combinations all-at-once
  • Helps remove testing hurdles
  • Acts as an early-bug-fixer


Parallel Testing in Selenium


We understand the concept of parallel testing quite clearly by now. Parallel testing in Selenium is a type of software testing wherein many apps and features are tested simultaneously in different environments, saving a lot of time and effort ensuring high-class product quality. Let us say, you want to test the functionality of a sign-up form and perform sequential testing on fifty different combinations of browsers and operating systems. Assuming each test takes two minutes to complete, the total time it will take to test the entire form would be hundred minutes. Unlike the above scenario, if we run four tests concurrently, the execution time will come down to just twenty minutes. That saved 80% of the time!


Parallel Testing in Selenium


Now, imagine how much time it would consume if the automation scripts have to run on other modules at the same time! Even if we automate the Selenium test suite, it will take forever to test the entire application.


Parallel Testing using TestNG and Selenium


We know, parallel testing is crucial for any DevOps testing Strategy. Cross-browser testing is important, and it is achievable with the help of TestNG and Selenium Webdriver. Sequentially testing multiple test scripts on different browsers can be time-consuming. TestNG, which is a Java testing framework, triggers parallel testing. It helps organize tests and execute them in a structured way. In Selenium, the testers can execute tests, classes, and methods using the ‘parallel’ attribute.  It all happens simultaneously in an auto-defined XML file, using the multi-threading concept of Java. Another way to achieve parallel testing in Selenium with TestNG is by setting the parallel attribute true in the data provider annotated method to pass complex parameters.


Why do we need Parallel Testing in Selenium?


With continuous integration, testers have to write different test scripts for each unique feature. The scripts will take time to run, and the only way to expedite testing and performing other QA tasks at the same time is Parallel Testing. So adopting parallel testing with Selenium becomes a crucial step towards an automated browser testing approach. Parallel testing is used predominantly in Selenium because of the cross-browser testing feature. Some of the reasons are as follows:


  • More Test Coverage: 

Parallel testing in Selenium provides better test coverage in a shorter period without compromising quality by allowing automated cross-browser testing. Parallel testing is a faster approach to testing as compared to sequential one. Using parallel testing, one need not run the test repeatedly for different OS and browsers. Instead, multiple parallel tests can run simultaneously.


  • Reduce Testing time: 

Parallel testing reduces the testing time, allows the QA team to run important tasks like focussing on the QA strategy. Unlike sequential testing, parallel testing allows running tests on multiple machines at-the-same-time, thus reducing the testing time. Moreover, the latter also removes the chances of human error so that the quality remains intact. Sequential testing is undoubtedly a comprehensive automated browser testing approach. However, it is neither productive nor delivers fast like parallel testing. And as mentioned earlier, it certainly increases the speed of testing by two times.


  • Cost-Effectiveness: 

Sequential testing is a long process requiring development, maintenance, and keeping the test environment updated all the time. Managing all these factors along with the expertise would shoot-up the cost of the QA department. On the other hand, parallel testing in Selenium is automated and cloud-based. So, there is no maintenance needed because the cloud infrastructure is always up-to-date with the latest changes.


  • Optimize CI/CD process: 

In the ever-evolving combined practices of continuous integration and continuous delivery, the testers need to run functional tests frequently. On the other hand, Parallel testing allows the QA team to save some time for fetch and analyze the bug reports of test data. The reports enable the developers to understand the problematic areas and quick-fix the bugs, therefore, optimizing the CI/CD process. This way, the developers can keep up the continuous integration practice and deliver faster. Reporting also improves the communication between the QA and Development team subtly.


  • Continuous Testing:

In the case of Continuous testing, the test cycle is faster. It is only feasible with the help of parallel testing in Selenium. Parallel testing also enables testers to make the best use of the cloud, allowing them to release quality products by performing more tests quickly. However, parallel testing can also be challenging sometimes. 


  • Limitations of the infrastructure

can be one of the reasons why your parallel testing is not successful. Maintaining own infrastructure can be unwieldy and will cost a lot. It would also not provide full test coverage as compared to other cloud-based testing solutions. To control the infrastructure, a team of skilled people would add to the cost. In this case, pCloudy provides the best cloud-based virtual configuration with multiple browsers, OS, and device combinations in a cost-effective way, making it easily accessible.  Saving time is indeed an important decision for internal resources. The decision of outsourcing the cloud-based testing grid instead of allocating it to the internal resources to manage the infrastructure is highly recommended. It allows testers to focus on strategy-focused tasks instead. 


  • Data dependency

is another common issue faced by testers when making a move towards parallel testing. A successful parallel testing needs test scripts to be independent of one another. It becomes challenging to make a reliable strategy if the test cases rely on some data. The test-scripts should be pre-configured with data that can be modified when there is a need for parallel testing. It will help the test to run successfully. The data dependency makes it hard to integrate parallel testing. Hence, it is important to write data-independent scripts to successfully execute parallel testing.


When to use parallel testing in Selenium?


Now that we have gained enough knowledge on how parallel testing in Selenium has done wonders in focused Continuous Integration and Delivery, it is necessary to know it in your software’s development life cycle.  Consider parallel testing in the following cases:

  • When the old and the updated version of the app is similar with minimal chances of uncertainty in their functionalities
  • Parallel testing can be used for homogeneous apps to figure out newer or older versions of the two, especially concerning financial applications.
  • When there is a case of a company’s transition from older to a newer system, utilizing it in importing legacy data transfers
  • Last but not the least. When an app needs to be tested across multiple browsers, Operating Systems, and devices during the automated browser testing.

Best Practices for Parallel Testing in Selenium

Keep Test Cases Independent: Make sure your test cases are independent of each other to avoid any unexpected results. One test case should not rely on the output of another test case. This allows you to run several tests concurrently without worrying about dependencies.

Use the Right Testing Frameworks: Frameworks like TestNG and JUnit can easily handle parallel test execution. They have built-in support for multi-threaded execution, making the process more manageable.

Design Scalable Test Suites: Your test suite should be designed with scalability in mind. It should be capable of handling a large number of concurrent tests if needed. Consider how your tests are grouped and organized.

Ensure Proper Synchronization: Race conditions are common in parallel testing. Therefore, proper synchronization methods should be used to handle shared resources effectively.

Properly Manage Test Data: Carefully manage test data to avoid inconsistencies. Each parallel test should have its own set of data to prevent any cross-test contamination.

Implement Retry Logic: Implementing retry logic in your testing framework helps overcome issues related to flaky tests or intermittent failures.

Continuous Integration: Integrate parallel testing with continuous integration tools like Jenkins to automate the testing process and get quicker feedback.

Browser and Device Coverage: Make sure your parallel tests cover a variety of browsers, operating systems, and devices to ensure your application works well in different environments.

Overcoming Challenges in Parallel Testing Using Selenium :

Managing Infrastructure: Setting up and maintaining infrastructure for parallel testing can be complex and costly. Using cloud-based solutions like BrowserStack or SauceLabs can help manage this challenge. These platforms offer ready-to-use test environments for a wide range of browser and OS combinations.

Dealing with Flaky Tests: Flaky tests are those that produce different results each time they are run, even if nothing changes. Reducing test flakiness can be achieved by ensuring tests are independent, robust, and reliable.

Handling Test Data: When multiple tests run concurrently, managing test data can be challenging. One approach to handle this is to use a unique set of test data for each test, preventing any conflicts or interdependencies.

Dealing with Synchronization Issues: In parallel testing, race conditions can occur when two tests access a shared resource simultaneously. Effective synchronization methods, proper isolation of test cases, and concurrency control techniques can help address this.

Skill and Knowledge: Parallel testing in Selenium requires a good understanding of Selenium, the testing framework (like TestNG or JUnit), and programming language (like Java, Python). Investing in training and continuous learning for your team is crucial to overcome this challenge.

Effective Logging and Reporting: With multiple tests running in parallel, logging and reporting can become a challenge. Using tools and practices that aggregate and visualize test results, such as Allure or Extent Reports, can help manage this.

By following these best practices and overcoming common challenges, you can make the most of parallel testing in Selenium and improve your testing efficiency significantly.




Parallel testing is considered one of the effective test approaches when it comes to achieving application quality, especially in the case of automated cross-browser testing. Parallel testing in Selenium brings cost-effectiveness, accuracy in results, improves test scripts, and optimizes CI/ CD process. It is achievable with the help of a competitive parallel testing strategy. An in-depth analysis of your parallel testing strategy and understanding its potential challenges would allow the organizations to adopt it within the organization entirely. It may also involve deciding whether to go for cloud-based testing grids or maintaining your test infrastructure, depending upon the requirement. Cloud strategy is critical when the testing team spreads across the globe. As much as we need an automated testing strategy, we should always be open to evolving with time to provide excellent test coverage while saving time and resources.



Parallel Testing in Selenium

Priyanka Charak

Tech Blogger - She writes about Technology, Mobile Application Development, Internet of Things, E-commerce, Computing and Design with the aim to coalesce new media and technology.

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