What is Regression Testing? Definition, Tools and Examples

regression testing

What is Regression Testing?

Regression testing is a systematic approach to software testing performed after modifications in the codebase. It ensures that new updates do not disrupt the existing functionality, maintaining software stability and performance.


This is because new code may bring in new logic that conflicts with the existing code, leading to defects. Usually, QA teams have a series of regression test cases for important features that they will re-execute each time these code changes occur to save time and maximize test efficiency.


If the project does not have a version control system, it can be tricky to locate the exact component that produces the bug. However, with regression testing, we know exactly where the bug comes from, enabling better troubleshooting. It is essentially a periodic health check-up for the software. Due to its highly repetitive nature, regression testing is a great candidate for automation testing.



Examples Of Regression Testing

Keep in mind that regression testing is a practice and method. There isn’t a testing tool for regression testing. Any test that was developed at the initial launch of a certain feature, brought up to run at later releases, is already a regression test. You can have regression tests by application attribute and type:

  • Attribute: visual, functional, performance, security
  • Application layer: UI and API
  • Application type: web, mobile, API and desktop
  • Granularity: end-to-end, integration and unit tests (test pyramid)

To perform regular check ups on existing code, regression testing basically involves:

  • Testers writing and building automated test suites
  • Testers and business analysts filtering out release-specific tests to re-run on affected areas from new releases

Let's consider a detailed example of regression testing for Etsy, an online marketplace for handmade and vintage items.


Etsy has decided to add a new personalized recommendation feature to enhance the user experience. This feature will suggest items based on users’ browsing history, past purchases, and interests. The goal of regression is not to test that new feature. Instead, our goal is to ensure that the new personalized recommendation feature does not disrupt the existing functionality of the website. This means we need to go back to core features to check if they are working as expected after the new feature is integrated.

Here are some test case ideas:

  1. Item Listing
  2. Search Functionality
  3. Cart and Checkout
  4. User Account Management
  5. Reviews and Ratings
  6. Payment Processing

You have 2 approaches to choose from: 

  1. Manual regression testing: manually perform all of the test steps and then record results in a test management system.
  2. Automated regression testing: leverage automated testing tools like Selenium to create scripts that test core functionalities.

Here is a sample test case for search functionality

def test_search_functionality():
    driver = webdriver.Chrome()
    search_box = driver.find_element_by_name("search_query")
    search_box.send_keys("handmade necklace")
    results = driver.find_elements_by_class_name("v2-listing-card")
    assert len(results) > 0, "Search results should not be empty."

The steps we did include:

  1. Open Browser
  2. Go to Etsy
  3. Find Search Box
  4. Enter Search Query ("handmade necklace")
  5. Submit Search
  6. Check Results
  7. Close Browser

Read More: Top Test Cases For Search Functionality

At a larger scale, companies whose business model revolves around their digital products need regression testing to frequently check up on their core features. To improve productivity in regression testing, automation testing tools are commonly employed.



Why is regression testing important in Agile and CI/CD?

Sometimes a mild modification can cause a domino effect on the product’s key functions that will take tons of effort to reverse.


Practicing regression testing aligns with the Agile testing methodology in continuously iterating, integrating and testing new code. Frequent releases mean better and faster feedback loops to not have a build up of broken code detected near the production date.


CI/CD is simply a series of automated tests. The pipeline is made to serve the objective of being able to continuously test while continuously pushing or integrating new code. Further analysis can also alter the scope to pinpoint optimization opportunities. For example, they can also aim to find defects but also to find opportunities for UX improvement.


Read More: A quick introduction to CI/CD concepts and best practices

Regression testing is not strictly about functionality. Visual regression testing is also employed to detect visual bugs that may occur due to changes in the codebase. 

For instance, when an internal code change occurs, the outdated UI elements may not work properly, resulting in non-clickable buttons or misaligned images. Instead of manually reviewing every single UI across hundreds of devices and browsers, QA professionals can simply execute a suite of automated regression tests to locate those visual bugs.

Read more: Types of Automation Testing Your Team Should Know

In other words, if your product undergoes frequent modification, regression testing will be the filter that ensures quality as the product is improved.


When is Regression Testing Done?

Why is regression testing important

Typically, regression testing is applied under these circumstances:

  • A new requirement is added to an existing feature
  • A new feature or functionality is added
  • The codebase is fixed to solve defects
  • The source code is optimized to improve performance
  • Patch fixes are added
  • A new version of the software is released
  • When changes to the User Interface are made
  • Changes in configuration
  • A new third-party system is integrated with the current system

All of these occasions involve a restructuring or adjustment of the current code, which may result in unexpected behaviors, hence the need for regression testing.

Regression testing the ideal candidate for automation testing due to its repetitive nature, with up to 65% of respondents of the State of Software Quality Report 2024 reporting that they have applied automation to their regression testing activities. To automate regression testing, it is common to leverage a regression testing tool to assist with the coding part as well as test case management, planning, and reporting.

Testing activities applying automation testing with regression testing being the most popular candidate for automation

→ Download the State of Quality Report 2024 to get the latest industry insights


How To Build Your Regression Test Suite?

Generally, a good rule of thumb is running checks on critical capabilities:

  • Features that makes up core business flows
  • Frequently used features

With test driven development, each new feature should come out with its own set of tests. For business instances like regression testing, test cases could be readily available for engineers or business analysts to pick out and run on-demand. However, there are always several crucial steps that should be followed.

regression testing steps

1. Detect source code changes

Identifying the impact and risk of the latest code change is key to building a solid regression test. Conduct code review sessions to identify the components or modules that were changed, as well as their impacts on the existing features. This can be achieved by leveraging a version control system such as Git to compare the differences between the old and new code.


2. Prioritize impacted areas and test cases

After that, QA teams discuss which changes should be extensively tested and which could bare with adequate testing. Modifications that have an impact on core features, or those that significantly alter how the application works, should always be the top priority. 


Defining priorities heightens in importance when the size of the codebase is bigger. The number of tests and time they take to complete could take up to months or an entire sprint. When talking the manual vs. automation testing narrative, regression testing is always the top candidate. 


Given its repetitive nature, teams and companies have standardized the process with automation testing. Whether they’re functional, performance or security checks, this exhaustive list of automation tools shows you the vendor and open source options you have for different testing purposes.


3. Determine Entry Point and Exit Point

Once the team agrees on which changes should be examined, they can select the tests that need to be performed. Generally, testing teams have a range of test suites ready to be executed, but they only have to execute only the relevant ones in each regression testing session. 


Essentially in this step the team formulates a step-by-step plan and prepares the right testing system to perform regression testing. It is necessary to also discard obsolete test cases or test suites for effective test management in the future. 


4. Categorize regression test cases

In this step, we deep-dive into the plan formulated in step 3 and categorize them by various factors. A few common test categorization criteria includes:

  • Manual vs automated regression tests: For ad-hoc or non-repetitive test cases, manual testing and human evaluation still make the most sense. Anything that involves the same series of test steps, over and over again, should be automated.
  • Critical vs non-critical features: evaluate test cases based on urgency and significance and assign them a value of importance (high, medium, low). Other factors can also be brought into consideration based on business requirements.
  • Testing types: each testing type calls for different setup, tools, and environment, so classifying test cases by type (for example functional/non-functional tests) can give the team better control over the testing activities. For the sake of simplicity, many testing teams have gradually adopted a centralized testing system from which they can conduct a wide range of test types without having to constantly switch between platforms

Read More: 15 Different Types of QA Testing


5. Test Environment Preparation 

Having test environments at hand at all times is important for frequent regression testing. As new code are being developed constantly, environments need to be stable and ready-to-test to not interfere with the planned testing schedule. In additional, poor environment setup can give tests more reason to fail, missed defects and false positive/negatives.

Big question: Leverage cloud environments or physical devices?

Overheads and delays in the release timeline can also result in operational inefficiencies. Setting up physical devices and machines involve engineers working with IT, Ops and finance to suffice the ongoing hardware, software, and maintenance costs. 

That’s the problem that cloud testing or on-demand cloud environments solve. Say you’re working with a web application for blogging and lifestyle, chances are you wouldn’t need upfront investment in physical hardware like a complex game application would. 

Indeed, coverage on different browsers and operating systems is still necessary, but cloud environments would make more sense. Applications with dynamic loads would benefit from the scalability advantage of being able to scale cloud resources up or down.


Read more: Explore Katalon TestCloud | Cloud-based Test Execution Environment.

Physical devices won’t be going anywhere either. Applications like games require exact customization on components like graphics cards, processors or memory to test the frame rates, load times and rendering quality. Aside from the default configurations of your physical machine, having a CI pipeline implemented is a standard for most development teams.


6. Schedule And Execute Tests

At this stage, all test cases are ready for execution. Teams can schedule test cases to run based on the plan. Certain test cases can even be scheduled to run periodically in intervals over the entire development cycle. Time-based test execution allows teams to have greater quality control over the constant changes of their application.


Is time-based execution to test constant changes one of your priorities in testing? If so, learn how to easily manage and set up time-based tests orchestration with TestOps.


7. Measure regression testing success

This stage gives important insights for future test runs. Analytics allows QA managers and other key stakeholders to quantify their testing efficiency and make data-driven decisions. Test reports can reveal weak points in the application for in-time adjustments for the development team.


Read More: How to build an effective regression test suite?


Top Regression Testing Tools

1. Katalon Platform


Katalon regression testing


Katalon Platform is a comprehensive end-to-end AI-augmented automation testing platform that can take your regression testing to the next level. It is the all-in-one regression testing tool for your website, web services, desktop application, mobile application and even API testing. 


Katalon Platform is a comprehensive test automation and quality management platform for UI-API integration testing. Katalon is dedicated to functional testing. This means you can develop and store web, mobile, API and desktop tests for regression testing. 


View a Demo of Katalon in Action!


Thanks to its Record-and-Playback features, any team member can easily capture test objects and record actions that simulate real users’ activity. This sequence can be re-executed in regression testing sessions, saving tremendous time compared to manual testing.


Katalon Platform also supports running scripts on a wide range of devices, browsers, and testing environments, allowing QA teams to perform a lot of testing activities in just 1 place instead of having to spend time configuring environments and constantly switching tools.


execute test cases in Katalon Studio


After executing tests, Katalon Platform enables teams to review test results with the comprehensive and customizable test reports in LOG, HTML, CSV, and PDF formats before forwarding them as email attachments. There is a debugging mode for testers to conduct a root cause analysis for a specific failed case. 


The platform integrates seamlessly into your CI/CD pipeline thanks to its diverse integration ecosystem. With its free forever version, Katalon Platform has nearly all of the features your team needs to start testing and bring value at no cost. If you are already testing on a framework, you can also migrate to Katalon Studio without losing any progress.


Not just that, Katalon Platform also comes with many exciting AI features:

  • StudioAssist: Leverages ChatGPT to autonomously generate test scripts from a plain language input and quickly explains test scripts for all stakeholders to understand. Learn more about StudioAssist in Katalon.
  • Manual test case generator: Integrates with JIRA, reads the ticket’s description, extracts relevant information about software testing requirements, and outputs a set of comprehensive manual test cases tailored to the described test scenario.
  • SmartWait: Automatically waits until all necessary elements are present on screen before continuing with the test.
  • Self-healing: Automatically fixes broken element locators and uses those new locators in following test runs, reducing maintenance overhead.


Take Your Regression Testing To The Next Level With Katalon Free Trial


2. Selenium

Selenium for regression testing

It remains among the top open-source solutions for browser-based and cross-platform regression testing. As a free automation testing library, Selenium brings testers the opportunity to create test scripts in whatever way they want. Selenium also supports automated test scripts that cycle through data sets and data-driven tests.


Read More: Katalon vs Selenium: A Detailed Comparison


This is a proper solution for large-scale quality assurance teams with advanced testers having expertise and experience. However, its steep learning curve usually is a challenge for small and mid-size teams. Moreover, automation testing scripts written with Selenium have to be continuously revised as code changes occur, which is time-consuming.


3. Watir

Water regression testing tools

Watir, or Web Application Testing in Ruby, is an open-source library using the Ruby programming language to facilitate OLE-based testing, eliminating the need for an external server. With its rich and intuitive interface, Watir allows users to easily create code without needing to read extensive documentation. 


The tool supports multi browsers and operating systems, and WATIR is equipped with the Attach Method, ensuring that when a linked domain window is opened, the original application window will remain connected. Another interesting feature of Watir is its capability to support diverse user interaction capabilities for website testing, such as clicking links, filling out forms, and validating texts.


4. IBM Rational Functional Tester

regression testing for IBM

Rational Functional Tester, or RFT, is a tool for software test automation from IBM. It offers automated testing for functional, regression, GUI, and data-driven testing, and is compatible with web-based, .NET, Java, Siebel, SAP, terminal emulator-based applications, and PowerBuilder.


IBM Rational Functional Tester features a natural language script editor and rendered screenshots for easy test visualization and editing, plus ScriptAssure technology that allows testers to automate tests that are resilient to frequent UI changes. 


Additionally, it provides a recorder of user actions, multiple customization options, script maintenance capabilities, and the ability to share functional tests with other team members and run them on hybrid environments.


5. Apache JMeter

Apache JMeter for regression testing

Apache JMeter is an open-source Java application for testing load, performance, and functional behavior of web applications. It has been expanded to include testing other functions, such as the efficiency and concurrent user request handling of a server.


JMeter's graphical interface, which is based on the Swing graphical API, is simple to use and can be run on any environment that supports a Java virtual machine, including Windows, Linux, and Mac. It is a great tool for functional performance and regression testing on different technologies.


Read More: Top 15 Performance Testing Tools Your Team Should Know


Regression Testing Techniques

Regression testing has three most prominent implementation methods, including retesting all, regression test selection, and test case prioritization.

1. Retest All

In this technique, regression testing is applied to all existing test suites. It is easy to see that although it is the safest way to ensure all bugs are detected and resolved, this method requires substantial time and resources. 


That is why the complete regression approach fits better in certain contexts. For example, only consider complete regression testing when an application-wide update occurs, such as when the application is adjusted for a new platform or language, or when the operating system gets a major update.


Another suitable use case for complete regression testing (or complete retest) is for small-sized applications. As the number of test cases to be executed is relatively low, QA teams can execute all of them for maximum coverage. Minimize effort to create a test suite with Parallel Testing.


2. Regression Test Selection

With this approach, QA teams may select the relevant parts that can be affected by the changes and perform regression testing on these chosen parts only. By picking out the related areas, you can apply limited and relevant test cases to reduce both the time and effort invested in regression testing.


This approach is suitable for more complex or large-scale applications, whose number of test scripts to be executed is higher.


3. Test Case Prioritization

This approach is essentially prioritizing test cases that must be included and performed first in the regression testing process. These test cases should be prioritized based on several criteria: 

  • Failure rate
  • Business impact
  • Gradually used functionalities
  • Test cases to check the functionality of new features 
  • Customer-centric features
  • Security-related features

There may be many other aspects to consider depending on the specifics of your business and organizations. It is important to understand how business requirements translates into the features of your application for better decision making.


4. Corrective Regression Testing

Corrective regression testing is simply re-running all current test cases when no code change has been made, yet. This practice is to double-check on whether the current code functions fine, and whether we can reuse the existing test cases or not. 


If the test results are positive, QA teams can be confident that their test cases are up-to-date. At this stage, testers can start the test planning and prioritization process while the new code is added.


5. Progressive Regression Testing

With progressive regression testing, testers acknowledge that changes to the code may call for changes in the test suites themselves, so they update the test scripts to align with the new requirements. This approach is employed when there is a change that impacts product vision.


Retesting vs Regression Testing

The two terms retesting and regression testing can be confusing for test automation novices. They might sound similar but are in fact entirely different from each other.


Retesting literally means “test again” for a specific reason. Retesting takes place when a defect in the source code is fixed or when a particular test case fails in the final execution and needs to be re-run. It is done to confirm that the defect has actually been fixed and no new bug surfaces from it. 


Regression testing is performed to find out whether the updates or changes had caused new defects in the existing functions. This step would ensure the unification of the software.


In a typical software development pipeline, retesting is performed before regression testing practices. Retesting solely focuses on the failed test cases while regression testing is applied to those that have passed, in order to check for unexpected new bugs. Another important note is that retesting includes error verifications, in contrast to regression testing, which includes error localization.


Moreover, automation is a crucial feature in regression testing, allowing you to make the most of your test case capabilities. Additionally, regression testing eliminates all underlying side effects caused by code changes in the most cost-effective way possible.


Agile Regression Testing

With the Agile development approach, teams can gain numerous benefits and values, such as accelerated time-to-market, ROI, customer support, and product improvements. However, this comes with a significant challenge of balancing between sprint development and iterative testing to avoid conflicts as the product matures.


Agile implementation of regression testing plays a key role in aligning the existing and updated functionalities, avoiding all possible rework in the future. Agile regression testing ensures the business functions are stable and sustainable.


On another note, regression testing helps developers to focus their efforts on building new functionalities for the application rather than keep on returning to check for defects in the old features. Applying regression testing reveals the unexpected risks in software builds, helping developers to respond more quickly and efficiently.

Final Conclusion

Regression testing is key to improving the overall quality of the product and user experience. The right regression testing tools can significantly identify all surfaced defects and eliminate them early in the pipeline. 


In addition, regression testing in Agile offers a host of technical and business advantages. Therefore, the more your organization invests in planning and performing regression testing, the more control you will have over the budget, process, and error mitigation of your product.


Up Your Regression Testing Game, Today