As software engineering teams increasingly embrace the CI/CD model, the responsibility to expedite product delivery to market while maintaining impeccable quality becomes more pronounced. Within the realm of Quality Assurance (QA), frameworks like Selenium help minimize the impact of bugs by conducting comprehensive testing at the earliest stages and swiftly identifying issues. 

For QA teams, this entails augmenting test coverage through automation. However, the magnitude of tests to be executed, coupled with the time constraints in assessing various features, often renders traditional sequential automated testing inadequate. Parallel testing emerges as a solution, enabling teams to simultaneously execute automated tests across multiple configurations. This approach effectively addresses constraints related to downtime and budget while enhancing test coverage and upholding quality standards.

From a retrospective view…

Historically, testing has played an integral role in the software development process, a practice deeply ingrained in the traditional waterfall approach. In this conventional testing landscape, testing primarily adopted a manual and sequential approach. Skilled testers were tasked with employing beta software to meticulously identify faulty components, including bugs and inefficiencies, and rectify them before the software’s official release.

However, this traditional paradigm witnessed instances where software made its way to the market despite harboring inherent issues. Some organizations, aware of these specific problems, chose to overlook them due to time constraints associated with exhaustive testing.

Over time, the software development landscape underwent a significant transformation with the emergence of agile software development methodologies and the segregation of Development Operations from IT Operations. This paradigm shift rendered the entire software development process more adaptable and scalable. It ushered in innovative automated testing techniques that played a pivotal role in reducing time-to-market—a critical factor in the success of software launches—while concurrently upholding stringent quality standards.

Parallel Testing

Parallel testing is a software methodology that harnesses the power of automation testing to simultaneously run identical tests across multiple environments, real devices, and browser configurations. This approach yields substantial time and resource savings in the testing process. During parallel testing, two distinct software versions are run concurrently using the same input. 

The objective is to assess whether the legacy system and the new system exhibit consistent or divergent behavior. This practice allows software testers to verify that the new system possesses the necessary capabilities for efficient software operation. Parallel testing can be carried out through the utilization of automated testing tools or by manual means.

In the realm of parallel testing, the automation framework seamlessly integrates with cloud-based solutions and virtualization technologies. This integration facilitates device management, enabling the concurrent execution of automated tests across various platforms.

Why Do We Need Parallel Testing?

  • Parallel testing simplifies testing methodologies, enabling software engineers to ensure functionality, quality, and other attributes to meet user expectations. Key reasons for implementing parallel testing include:
  • Streamlining large-scale testing for organizations, enhancing business processes and increasing revenue
  • Conducting redundant testing to ensure the new app version aligns with client requirements.
  • Demonstrating consistencies and inconsistencies between the new and old versions while preserving the integrity of the new app.
  • Verifying changes in data format between both versions

Determining the Right Time for Parallel Testing

Now that we’ve gained insight into how parallel testing functions and its potential to streamline test execution timelines, let’s examine specific scenarios where parallel test execution proves advantageous:

  • Ensuring Cross-Device and Configuration Compatibility: Parallel testing becomes particularly valuable when the software engineering team harbors uncertainties about an application’s functionality across diverse devices and configurations. This is especially relevant in regression-like scenarios involving an updated version of the application.
  • Seamless Legacy Data Migration: Parallel tests are exceptionally useful when migrating legacy data from an older system to a newer one. They play a pivotal role in verifying the seamless transfer of all data using an automated regression test suite.
  • Automated Browser Testing: Parallel testing is indispensable in cases of automated browser testing, where an application necessitates testing across a myriad of browser combinations, operating systems, and devices.

An Approach to Parallel Test Creation

A widely adopted method for parallel testing involves the creation of a suite of projects dedicated to testing browser compatibility, complemented by a master project responsible for testing the aforementioned suite of projects. Once this setup is in place, it becomes imperative to establish a set of Entry and Exit Criteria.

Entry Criteria encompass essential prerequisites that must be fulfilled before the commencement of test execution. These may include:

  • Configuring a suitable test environment, such as Selenium with TestNG
  • Defining pre-conditions and test scenarios is essential for the automated browser testing process
  • Migrating any necessary new or legacy data

Exit-level criteria shift the focus towards post-execution considerations, such as:

  • Evaluating discrepancies in terms of their impact on test suite execution
  • Assessing the output of the new system in comparison to the legacy system, where applicable

Implementing Parallel Testing: A Step-by-Step Guide

The successful execution of parallel testing requires a precise series of steps to be carried out by the testing team:

  • Simultaneous Execution: Ensure that both the old and new versions of the application are run concurrently.
  • Identify Differences: Thoroughly identify and evaluate the discrepancies between the two systems.
  • Consistent Input: In the event of disparities between the systems, maintain consistency throughout the Software Development Life Cycle (SDLC) by providing identical inputs.
  • Evaluation of Outputs: Following the execution of these steps, evaluate the generated outputs meticulously.

Benefits of Parallel Testing

Parallel testing, which relies on running virtual machines in the cloud, offers a multitude of advantages that go beyond time-saving. The key benefits of parallel testing encompass:

  • Expanded Test Coverage: Parallel testing provides access to a vast array of different devices, platforms, and configurations in the cloud. This extensive coverage enhances the breadth of testing, enabling the creation of a single test on a local machine and its simultaneous execution across macOS or Windows browsers.

A cloud-based AI-powered test orchestration and execution platform like LambdaTest offers a solution by providing access to a vast array of platforms, browsers, and their respective versions via the cloud. This allows users to execute automated parallel tests across multiple browsers and versions seamlessly.

Leveraging LambdaTest’s real device cloud, which offers access to over 3000 real browsers and devices, streamlines the testing process and enhances coverage, contributing to an agile testing approach. 

  • Cost-Effective Solution: Leasing test time from cloud services is a cost-effective alternative to building and maintaining an internal testing infrastructure. Additionally, cloud-based testing grids support high-concurrency testing, leading to a significant reduction in the cost per test.
  • CI/CD Process Optimization: Parallel testing seamlessly aligns with continuous integration and delivery (CI/CD) practices. It enables teams to execute tests as soon as developers submit new code updates throughout the software development lifecycle. Timely reporting and rapid feedback foster improved communication among different departments.
  • Enhanced Testing Practices: Parallel testing has the potential to elevate QA practices within an organization. The ability to conduct a higher number of tests in a shorter time frame allows QA teams to refine their testing methodologies and promptly identify and address bugs and vulnerabilities.

Limitations of Parallel Testing

Parallel testing, despite its numerous benefits, is subject to several challenges that can impede the testing process, making it more time-consuming and costly. Some of these limitations include:

  • Complex Dependencies: Parallel testing can become impractical when the components of a project are tightly coupled, making it difficult to separate them. Efforts to uncouple these components can be substantial, and high interdependence can hinder the effective use of parallel tests.
  • Flaky Tests: Test flakiness can occur for various reasons, such as reliance on test orders, insufficient resources, or external dependencies. Dealing with flaky tests can be time-consuming, and testers may need to address underlying issues rather than rely on short-term solutions like re-running or ignoring false negatives.
  • Resource Management: Effective resource management is essential for parallel testing. Testers must have a comprehensive understanding of factors like the number of tests to run in parallel, browser configurations, testing duration, RAM requirements, and process locking times before initiating testing.
  • Multiple Browser Issues: While parallel testing allows for cross-browser compatibility testing, its coverage of multiple browsers may be limited in practice. This can pose challenges when ensuring compatibility across a wide range of browsers and versions.
  • Automation Expertise: Parallel testing demands a deep understanding of the product and its functionalities. It requires the expertise of an automation specialist well-versed in parallel testing methodologies.

Parallel Testing Best Practices

The advantages of parallel testing can only be realized when we adhere to the following best practices:

  • Implement Independent Tests: Each test should function independently and not rely on the outcome of another test. Parallel tests may execute in varying orders, so interdependence can lead to unpredictable results.
  • Focus on Single Features: Leverage the modular nature of parallel testing by testing one feature at a time. Testing multiple features within a single test defeats the purpose of quickly identifying failures, which is essential for efficient CI/CD pipeline performance.
  • Avoid Static Objects: Refrain from using static objects that may hinder other parallel tests from making necessary modifications.
  • Reset Test Data: Prevent data cross-contamination by adopting a modular approach to create, utilize, and clean up test data. This ensures that each test leaves the system in the same state in which it found it.


Parallel testing is recognized as one of the most effective methods for enhancing the efficiency of CI/CD pipelines while reducing risks, resource demands, and expenses. It plays a pivotal role in cost reduction and enables the execution of test cases concurrently, improving script accuracy. 

The demand for conducting compatibility testing through parallel testing has grown due to the necessity of accessing various platforms and browsers simultaneously. However, this approach can escalate costs, and there may be limitations in obtaining access to all required browsers and versions. The current market offers a wide range of parallel testing tools, facilitating the adoption of this approach to optimize the entire software development lifecycle.


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