What Is Parallel Testing? Every Detail You Need

Parallel Testing

Parallel testing is a widely used, highly efficient software testing technique that you surely use most of the time, but may have a little in-depth idea about it. So, here we are going to focus on knowing it in detail.

What Is Parallel Testing?

Parallel testing is the method of running multiple test cases parallelly at once to test multiple applications or their components in a simultaneous order to reduce overall testing time. As this process sounds so simple, it is actually quite easy to perform. You just need to use an efficient test automation tool like Preflight to take care of everything.

However, you must have some operational concept about this important topic to achieve better results. Hence, let’s get started with it.

Why Should You Perform Parallel Testing?

Parallel testing is indeed a highly efficient approach, but if we consider it more technically, the following points are the reasons to prioritize it.

  • Technical products come up with new versions in very short intervals. Parallel testing lets you ensure that the new versions are working properly in all forms of popular environments.
  • Parallel testing lets you check if the consistencies are the same between new and old versions.
  • Through parallel testing, you can check if the data formats between the two versions have changed.
  • Parallel testing allows you to check the integrity of the new applications.

How Does Parallel Testing Work?

As you know, testing means confirming that the software as well as all its components are working as expected. Hence, in parallel testing, what you need to do is that you have to run two or more versions of the same software concurrently with the same input or test methods.

Now, while parallelly running multiple versions of the software leads you to test the correctness of those versions, to check the cross-browser & cross-platform compatibility of one single version of an application, you have to run that version simultaneously on different devices and different browser-OS combinations.

When To Do Parallel Testing?

Though parallel testing is an overall efficient approach to software testing, there are a few ideal situations where parallel testing is the most effective way to achieve the best results. Let’s check them out below.

  • When the company is transitioning from the old system to the new system.
  • When the legacy data is being imported from one system to another.
  • When two systems are being synchronized.
  • When all the outcomes should be defined more precisely. e.g. in the domains where most operations are based on calculations and the outcomes have specific formats.

How You Should Do Parallel Testing: The Complete Approach

The widely used effective approach to perform parallel testing is creating several projects to test different parts of the application and one large project to run all those small projects. Those small projects are called Slave projects and the large one is called master project.

Parallel testing has two level criteria that are -

  1. Entry Criteria: These are the criteria that must be met before proceeding with the parallel testing so that the test cases can be smoothly run.
  2. Exit Criteria: These are the criteria that state a successful conclusion of the parallel testing stage.

The crucial pre-flight checks to be completed before moving on with parallel testing are -

  • Environment setup must be completed before beginning parallel testing.
  • Remember to first define all pre-conditions and scenarios.
  • Legacy data and new data must have a successful migration.
  • Parallel tests can be stated as completed only after all exit criteria are satisfied.

The steps to perform parallel testing are -

  • Step 1: Running an old system against a newly developed system.
  • Step 2: Understanding the difference between both systems.
  • Step 3: Going through the complete cycle using the same input.
  • Step 4: Measuring the output of the newly developed system compared to the old system.
  • Step 5: Reporting the causes of the bugs if found.

Parallel Testing Best Practices

Some best practices and tips & tricks for achieving the best results through parallel testing are mentioned below.

Typically Found Bugs In Parallel Testing Are -

  • Changes in the internal logic.
  • Changes in the flow of products.
  • Major functionalities are modified.

Required Number of Cycles Should Be Determined As -

  • The number of testing cycles depends on the complexity of the module.
  • You should run multiple scenario cycles using predefined test data that was passed from the previous system.

Categorize Based On Differences

While running the parallel testing cycle, remember to measure the results of both the new and legacy systems line by line with the differences highlighted. Also, define every captured difference as per the type of error.

Note Down The Following Things During Cycles To Determine The Type of Error

  • Entry error
  • Error due to the old system
  • Explainable or acceptable difference
  • Unexpected error

Differences Between Traditional Testing and Parallel Testing

Traditional Testing

Parallel Testing

Tests one software only.

Tests the updated application against its previous version.

Cross-browser or cross-platform testing.

Runs the old scenario with new software with reserved input conditions.

The objective is to find out the design issue.

The objective is to find out the outcome as per the previous system.

You don’t need to know any difference with another software or any previous version of itself.

You should have knowledge about the old and newly developed system.

Benefits of Parallel Testing

Parallel testing has gained popularity for its prime benefit of accelerating execution across multiple versions.

However, it also offers a number of benefits that we have jotted down below -

Accelerate Execution

Let’s elaborate on the prime benefit of parallel testing. Accelerating execution lets you significantly save a lot of time. For example, if you have to run 100 tests while each one of them takes 2 minutes to get executed, and if you try to run them one by one synchronously, it will take you 200 minutes to complete running them. But, parallel testing can allow you to run all the 100 tests simultaneously, and you can complete running them in 2 minutes. So, when you are performing tests on a large scale, parallel testing can save you a lot of time.

Improve Test Coverage

You surely know how important it is for a tech business to achieve as much test coverage as possible. Parallel testing is one of the most efficient approaches that significantly improve the overall test coverage.

As it allows you to test across multiple devices and multiple browser-OS combinations at the same time, you become capable of achieving remarkably high test coverage in much less time while you can also ensure that your application is compatible with every environment and every situation.

Break Through The Testing Bottleneck

Testing often becomes a bottleneck of DevOps. While the long & time-consuming traditional testing process does nothing to get rid of the bottleneck, parallel testing exempts you from that hassle. It accelerates testing and lets you ensure great product quality while the product is already live.

Faster Debugging

Besides allowing you to execute multiple tests on different devices and environments at the same time, parallel testing also enables you to fix the bugs during the test sprint. That makes it possible for the developers to focus on creating new features rather than staying stuck with testing the existing ones.


Parallel testing sounds like a very simple term, but in terms of significance, it holds a highly important place among efficient software testing strategies. This article provides you with an in-depth understanding of it and lets you know how it helps you in improving your overall testing efficiency. So, we suggest you carefully go through every detail and acknowledge yourself with a crucial method of achieving higher test coverage.

Also, you must know that parallel testing can be effectively implemented only when you use an advanced testing tool that allows you to test your product across multiple platforms and environments. And, we must mention that Preflight is one of the most renowned advanced AI-based test automation tools that can fulfill all your testing needs within seconds. It has gained and held its popularity by allowing everyone to create, run, and manage complex tests regardless of their coding knowledge. You can get detailed information about the advantages of using this tool from the article “10 Amazing Software Testing Benefits From Preflight In 2022”.

An amazing testing experience is waiting for you to sign up for free. Visit our website or reach out to us for more information. Also, if you like to read informative tech articles, do consider checking out our blog page.