Regression Testing: A Complete Guide

Regression testing is the process of re-running existing tests after making changes to the code, to make sure the changes didn’t break anything that was working before.

Why regression testing is necessary? Because as modern applications grow more complex and interconnected, a small code update can ripple through the system and cause unforeseen issues elsewhere. Therefore, when the codebase is updated, regression tests must be executed to check up on the existing features to see if that update breaks anything unexpectedly.

A bug found during a regression test is called a regression.

Examples of regression testing

Let's imagine that you're testing an e-commerce app called VeryGoodEcommerce.

The current features of your app include:

• Product browsing
• Search functionality
• Price calculation
• Payment processing
• Inventory updates.

One day, the dev team decided to add a new feature that allows users to apply discount codes at checkout. It's a fascinating feature, and beta users love it.

However, we can never know how that shiny new feature interacts with the current features.

What if it breaks the Product browsing? What if it breaks the Price calculation? 

That is why regression testing is needed. Instead of testing the new feature, you run tests for the five existing features to make sure that the new Discount feature didn't negatively affect them.

If the discount feature affects some feature (for example, price calculation), we call that a regression. The dev team is immediately informed of the issue for immediate troubleshooting. 

If the discount feature does not negatively affect anything, there is no regression, and everyone is happy. The new feature is then rolled out for users to enjoy.

Benefits of regression testing

• Prevents Domino Effect on Key Functions: Even minor modifications in the code can cause a rippling effect across the entire product’s key functionalities, and you need regression testing to detect these issues early.
• Aligns with Agile Methodology: Regression testing is all about iterating, integrating, and testing new code, and Agile is all about that. Their nature aligns with each other so seamlessly, making regression testing a part of Agile culture itself.
• Supports CI/CD Pipelines: Similar to Agile, CI/CD relies on running automated tests to ensure that new code integrations are continuously tested, which makes regression testing an integral part of it.

📚 Read More: Regression Testing in Agile: A Complete Guide

Challenges of regression testing

1. Time-consuming: every time you add or tweak a feature, you need to re-test everything. If your project is large and complex, a simple update can turn into a marathon of tests very quick. Without proper automation built in for regression testing, regression testing becomes a huge time-sink for everyone, and QA becomes a bottleneck.
2. Test suite maintenance: as your application grows, so does your regression test suite. Keeping those test cases up-to-date is a continuous efforts where you have to add new tests, remove irrelevant ones, update old ones. The "update-old-one" is especially important for UI test cases because it is ones that go through the most frequent changes.
3. Risk of overlooking bugs: when the pressure’s on to release quickly, it’s easy to overlook smaller parts of the system. Maybe a feature that worked flawlessly in previous releases suddenly breaks, and no one noticed. The more complex your app becomes, the higher the chance of missing hidden bugs lurking in the shadows.

When is regression testing done?

Typically, regression testing is done when:

• 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

Retesting vs Regression testing

The terms "retesting" and "regression testing" are usually misused. It is important to differentiate them:

• Retesting literally means “test again”. It means testing something again after a bug has been fixed. If a test failed earlier, you re-run it to make sure the issue is really gone and the fix actually works.
• Regression testing checks the rest of the system after changes are made. It helps catch any new bugs that might have been introduced by the fix or update, making sure everything else still works as expected.

In simpler terms:

Regression testing vs. New feature testing

You can think of "New feature testing" is the opposite of "regression testing". Put simply:

• Regression testing checks old/existing features.
• New feature testing checks new features.

Together they ensure quality across the entire application. Here is a simple comparison table:

How to do regression testing?

1. Detect source code changes

First, your team needs to identify what was changed and where it happened. From our experience, the most common reasons for code changes are usually:

• Bug fixes
• New features
• Enhancements
• Configuration changes

2. Prioritize impacted areas and test cases

Not all changes have the same level of risk. Doing regression testing for everything would be ideal, but in reality, time, budget, and resources are limited. Prioritization helps ensure you're focusing on areas that are most likely to break, reducing wasted effort on areas that aren’t impacted by recent changes.

Some features or components of an application are more critical than others. Modifications that have an impact on core features, or those that significantly change how the application works, should always be the top priority.

Consider:

• Scope of code change
• Business criticality
• Frequency of use
• Historical defect density
• Interdependency
• User feedback
• Pain points

📚 Read More: How to Build a Regression Test Plan?

3. Determine entry point and exit point

This step is crucial because deciding when to start regression testing ensures that the environment is ready, the codebase is stable, and the test objectives are well-defined. Common entry points for this are:

• Build passes smoke testing.
• All development tasks and bug fixes related to the current release are complete.
• The test environment is fully set up and mirrors production.
• Test data is available and ready to be used.
• Regression test cases are prepared and prioritized.

Exit points, on the other hand, defines when testing can be considered complete. This ensures that sufficient testing has been done to meet quality standards before the software is released or moved to the next phase.

4. Categorize regression test cases

In this step, we deep-dive into the plan formulated in step 3 and categorize them by several factors:

• 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. Due to its highly repetitive nature, regression test is the perfect candidate for automation testing.
• 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.

📚 Read More: 10 Best Practices for Automated Regression Testing

5. Test environment preparation

Having test environments at hand at all times is important for frequent regression testing.

As new code is being developed constantly, environments need to be stable and ready-to-test to not interfere with the planned testing schedule. In addition, poor environment setup can give tests more reason to fail, missed defects and false positives/negatives.

📚 Read More: How to Set Up Test Environments

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 test 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.

📚 Read More: Test execution: A Complete Guide

7. Measure regression testing success

This stage gives important insights for future test runs. Comprehensive analytics generated from test results enable QA managers and other key stakeholders to quantify testing efficiency, assess resource utilization, and measure the effectiveness of the testing strategy.

Here is how a test report may look like. In Katalon TestOps, after running regression test suites, QA teams can access the dashboard with rich insights about the effectiveness of that test run.

Should regression testing be automated?

Yes, regression testing should be automated. Here's why:

• Regression testing fits all of the criteria for automation: it is repetitive, high-volume, and predictable. Manual regression testing is just tedious and not scalable at all.
• Automated regression testing supports Agile and CI/CD workflow: regression testing is a backbone of continuous testing. Without automation, your CI/CD pipeline is half-baked. Automated regression tests act as safety nets, catching bugs early before they snowball into production incidents or broken features.
  Automated regression testing opens up the gate to scale QA: Modern software development is fast, iterative, and CI/CD-driven. You might deploy daily or hourly. You simply cannot manually re-run hundreds or thousands of test cases every time. Automated regression tests can run in minutes across browsers, OSes, and devices (while you sleep).

However, sometimes manual regression testing still makes sense:

• Exploratory testing: When intuition, curiosity, and user empathy are needed.

• UI/UX validation: Human eyes still catch layout glitches and visual regressions better.

• Highly dynamic interfaces: Where the cost of automation maintenance outweighs the benefit.

• Short-lived features: If a feature will be deprecated soon, don’t waste time automating its tests.

📚 Read More: Manual Regression Testing vs. Automated Regression Testing

How to balance regression testing and new feature testing?

Let's meet Alex Martins, with 20+ years in software quality and test automation at Fortune 500 companies, sharing his thoughts on how to automate regression tests if you're team are spending all of the resources for new feature testing:

How to automate regression tests?

Step 1: Know what you need to test

Focus on the parts of your app that break the most or matter the most, like checkout in e-commerce. Use code coverage tools, bug history, and your own experience to decide what needs testing. Don’t just test everything blindly.

Step 2: Pick the right regression test cases

Not every test should be automated. Automate the tests that are:

• Repetitive

• Stable

• High-impact

Good examples: login, form submission, backend calculations. Leave the messy, unpredictable stuff (like exploratory testing) to humans.

To decide which test cases are suitable for automation, we usually use a Test Case Selection Matrix, which is a practical scoring system that helps you evaluate test cases based on meaningful criteria. It brings objectivity and structure to your automation decisions by focusing on five key factors:

• Run Frequency – how often the test is executed

• Stability – how consistently it behaves across builds

• Business Criticality – how important the feature is to users or revenue

• Reusability – whether the logic is shared with other tests

• Manual Effort – how painful it is to do by hand

Here's how it works:

• List down the factors that you deem as "worth automating"

• Score each factor from 0 to 1

• Add up the total (max = 5)

• Set a cutoff (e.g., 3.5+ = worth automating)

Use the matrix during backlog grooming, test planning, or automation roadmap reviews to focus your efforts where they matter most.

Here's an example:

You can totally establish a different weighting system depending on your needs.

Step 3: Choose your tools

You’ve got two paths:

• Build your own test automation framework

• Use off-the-shelf tools (like Katalon, Selenium, etc.)

Pick based on your team’s skills, time, and long-term goals.

📝 Here's a list of best automated regression testing tools we've curated

Step 4: Run your tests smartly

There are 3 common ways to run automated tests:

• Batch runs: Group similar tests together.

• Scheduled runs: Run tests on a timer (e.g., every night).

• CI/CD runs: Run tests automatically with each code update.

Decide where to run tests: local machines, mobile devices, cloud platforms, or headless browsers. If you can’t afford all the devices, use cloud services like Katalon TestCloud.

Regression testing techniques

1. Retest all

This technique involves re-running the entire test suite to ensure that recent changes have not introduced new defects.

Although highly reliable, this technique is expensive and time-consuming, without much room for strategic considerations. This makes it less practical for large applications with frequent updates.

2. Regression test selection

Instead of testing everything, this method selects a subset of test cases that are most relevant to the modified code. It balances cost and efficiency by focusing only on affected functionalities.

3. Test case prioritization

This technique ranks test cases based on their importance and likelihood of detecting critical defects. High-priority test cases are executed first, ensuring that significant issues are caught early.

Types of test case prioritization:

• General prioritization: Focuses on test cases that provide long-term benefits across multiple software versions.
• Version-specific prioritization: Targets test cases that are particularly relevant to the current version of the software.

4. Hybrid regression testing

A combination of regression test selection and test case prioritization, this approach optimizes efficiency by selecting only the most critical test cases while ensuring they are executed in order of priority.

Best practices of regression testing

1. Prioritize test cases: Not all tests need to be run every time. Focus on critical functionalities, high-risk areas, and recently modified components to ensure efficiency.
2. Automate where possible: Manual regression testing is slow and prone to human error. Automate repetitive and high-impact regression test cases to speed up execution and improve accuracy.
3. Test suite maintenance: As the application evolves, so does the regression test suite. Regularly update test cases, remove obsolete ones, and ensure test coverage remains relevant. Here are some advice to build an effective regression test suite.
4. Continuous testing in CI/CD pipelines: Integrate regression testing into the CI/CD workflow to catch defects early, provide quick feedback, and reduce last-minute surprises before release.
5. Parallel testing: Running tests in parallel across multiple environments and devices significantly reduces execution time, making regression testing more manageable for large applications.

Top regression testing tools and frameworks

Manual regression testing can be tedious and inefficient, especially when the same test steps need to be repeated for each iteration. Using a regression testing tool is a more effective approach. These tools enable you to create an automated regression test suite that can be run in batches whenever a new build is available.

1. Katalon

Katalon have helped QA teams around the world quickly automate regression tests for web applications, API, and mobile apps.

With a Katalon license, Automation Testers and QA teams can:

1. Gain access to Katalon's pre-built test automation frameworks to automate without having to build from the ground up.
2. Write test cases in Java/Groovy with our Page Object Model framework. If you're unfamiliar to coding, simply choose a keyword from Keyword Library to automate the action you need. You can create custom keyword for any action you want, then plug it into Katalon's IDE.
3. Execute regression tests locally, on-cloud, or remotely with Katalon's extensive list of environments in TestCloud.
4. Manage and schedule test execution in Katalon TestOps. You can also manage manual testing activities with Jira integration.
5. Integrate Katalon into your CI/CD pipeline to do parallel testing.

2. Selenium

Selenium is a popular tool for regression and web application testing due to its flexibility and compatibility with major browsers (Chrome, Safari, Firefox) and operating systems (macOS, Windows, Linux).

Key features:

📝 Read More: Katalon vs Selenium: A Detailed Comparison

3. Playwright

Playwright is a modern end-to-end testing framework known for its speed and versatility across multiple languages (JavaScript, TypeScript, Python, C#, Java). It’s widely seen as a strong alternative to both Selenium and Cypress.

Highlights:

• Seamless execution across Chromium, Firefox, and WebKit with noticeably faster test runs compared to Selenium. Works well for both web automation and API testing.

• Ships with auto-waiting, screenshot capture, tracing, and a powerful codegen tool for recording interactions and generating test code. Great for teams wanting immediate productivity out-of-the-box.

• Official bindings for JavaScript/TypeScript, Python, Java, and .NET (C#). TypeScript is the most mature and best-documented, though Python and C# also work reliably for most scenarios.

• Easy parallel execution and test isolation at the process level without requiring third-party tools. This is a key advantage over Cypress, especially for scaling test suites.

• Auto-waiting for UI elements reduces the need for custom sleeps or explicit waits.

• Designed from the ground up for modern web apps. Works well with GitLab, Azure, Docker, and WSL, though some users report rougher setup experiences in non-TypeScript environments.

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. 

With Katalon, you can write regression tests in no-code, low-code, and even full-code mode for maximum flexibility, schedule them, then execute across environments.