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Parallel Testing

Friday 05 of March, 2021.
Reading Time: 3 minutes.
By Regina Argote Paez

What is it?

Also known as parallel execution, parallel testing tests different modules or applications in several browsers simultaneously instead of executing tests one by one. The objective is to reduce the time it takes to run tests. 

Parallel testing helps to reduce time and effort when executing tests, leading to quicker deliveries.

The opposite of parallel testing is sequential testing, where tests are run one by one. This testing approach takes up more time, resources, and effort. 

How Does it Work?

In parallel testing, a QA engineer executes two or more versions of a software at the same time using the same input or testing method. Alternatively, a single software version can be performed simultaneously on several devices or a combination of browsers and operating systems. 


  1. Faster execution: parallel testing helps QA engineers run tests in different browsers simultaneously, resulting in better test coverage over a shorter time.
  2. Broader test coverage: improved test coverage is another benefit of parallel testing since simultaneous tests can be run on a greater number of mobile devices or combinations of browsers and operating systems. Extended test coverage helps to mitigate risks and reduce the possibility of errors going unnoticed. 
  3. Eliminates testing bottlenecks: frequently, testing becomes a bottleneck in a DevOps pipeline. Time-consuming tests can delay the entire software life cycle. Parallel testing helps eliminate this type of bottleneck, speeding up test executions, reducing risks, and enabling continuous quality visibility. 
  4. Errors are fixed early on: parallel testing allows errors to be rectified during the sprint, not afterward; this significantly reduces the time it takes developers to correct any issues, giving them more freedom to innovate and create new functionalities instead of having to focus on fixing defects.


Is Parallel Testing as Precise and Complete as Sequential Testing?

Parallel testing is even more precise and complete than sequential testing. The latter has been the standard in software development and other fields not because it is superior to other types of tests but because in many ways, it is still the easiest and most practiced way of organizing and running tests. 

How Does Parallel Testing Work in Selenium’s Automation?

Parallel testing in Selenium is a process that allows the same tests to be executed simultaneously in different environments. The main objective of running parallel testing is to reduce the time and effort required to run automated testing in the browser while at the same time guaranteeing quality by using the Selenium Grid. 

Sequential testing scenario:

Parallel testing scenario:

When Should Parallel Testing be Applied While Using Selenium?

Parallel testing can be applied in the following scenarios:

  • When tests need to be run simultaneously on different machines using different browsers and operating systems
  • When it’s necessary to broaden test coverage
  • When it’s necessary to speed up regression testing for multiple software versions
  • When the company is migrating from an old system to a new system
  • Parallel testing in Selenium can be used to verify older as well as recent versions of an application


Executing faster tests and a higher number of tests results in more frequent software version releases and increases the number of detected errors. The math is simple. Parallel testing can prevent delays in delivery without compromising quality, making it superior to sequential testing. It also reduces quality assurance expenses as well as the cost of failed tests. Additionally, it optimizes processes and improves scripts continuously to obtain more accurate results. Finally, parallel testing reduces the risk of a client dissatisfaction due to an application’s quality.




  1. Parallel testing tests different modules or applications in several browsers simultaneously instead of executing tests one by one.
  2. Some of the benefits of applying parallel testing include faster execution, broader test coverage, elimination of bottlenecks, and fixing errors early on in the software life cycle.
  3. Parallel testing can prevent delays in delivery without compromising quality, making it superior to sequential testing.


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