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Modern software is ever-changing. Especially when working in an Agile environment, where releases are done very often, sometimes even in continuous delivery. New features are always added, existing features are changed, and bugs are fixed. And this is, of course, a good thing.

But at the same time, the risk of breaking existing working functionalities is relatively high. That’s why we need regression testing. In short, regression testing is a technique that validates that new changes in the code have not introduced new bugs. 

I’ll discuss regression testing, a critical quality assurance practice, in more detail below.  

What is Regression Testing?

Regression testing is an important part of the software development life cycle. It’s a type of testing executed to ensure that code changes did not impact existing functionalities and that what worked before these changes still works. Any issues found during this process are considered regression defects and should be treated with great priority.

Regression testing can be performed both manually and through automated tests. Automating the regression test suite is a good idea, especially when working with large applications, where the entire regression process can be very time-consuming.

Why is Regression Testing Important in Software Development?

When new code is added to the codebase, be it a bug fix or new functionality, it can impact already working code by introducing new defects or impacting non-functional aspects of the application, such as performance or usability.

This can lead to inconveniences for the end-user, who would probably not be very happy that what used to work isn’t working anymore. This, in turn, can cause revenue losses and have a big impact on the company’s reputation.

Regression testing helps catch these bugs early and contributes to having a fix before moving into production. This means that the customers will see a more stable version of the application without impacting the old functionalities they were already using.

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Test Case Selection

The first thing testers need to do before starting the regression is to identify the regression test cases to be executed. There are two main methods for test case selection: reactive and proactive.


In reactive test case selection, the quality assurance team takes action post-modification. This means that the test cases to be executed will be selected after the development team makes the changes to the code.


In the practice approach, the testers anticipate possible changes before the development modifications and build the testing plan accordingly. Deciding between these two methods depends on certain factors, including cost, complexity, coverage, and time constraints.

Test Case Prioritization 

Test case prioritization is probably one of the most important steps in the design of a regression plan. It helps in managing time effectively and improves the rate of fault detection. The first thing to do is to understand which areas are the most affected by recent changes, as well as decide on the time the team has to perform the regression testing. As one of the famous testing principles states, “exhaustive testing is impossible,” which means that we cannot cover all existing test scenarios and edge cases, but we can aim for the best test coverage we can achieve.

With this in mind, testers need to make a risk assessment - decide which areas are most critical to test and which are most likely to cause issues. Speaking of testing principles, remember that defects tend to cluster, i.e. an area with issues is more likely to uncover the most defects. In the case of regression testing, these will be the areas that have been changed.

Another thing to consider is whether or not we are using test automation. The automated test execution can run independently, and testers can focus more on experience-based testing, like exploratory and ad hoc, as well as on parts that cannot be automated, such as making sure that the user experience was not decreased in some way.

As the software is changed, it’s also important to update existing test cases to reflect the new changes or mark obsolete test cases accordingly so they are not executed by mistake.

Techniques & Tools for Effective Regression Testing

regression testing definition infographic
The Retest All techniqueSelective technique Prioritization technique
Also known as complete regression testing, this is the most rigorous regression testing technique. It involves retesting every feature within the software after any modification. It aims at 100% test coverage and requires re-running all existing tests and executing new test cases.

This technique is mostly suited for automated regression testing if most of the test suite is automated. It is the safest technique but not very effective when done through manual testing since it can take a lot of time to go through the entire regression suite.
This is a partial regression testing technique, where the team retests only the features impacted by the changed parts of the code. This is closely related to the regression test selection.

A regression test suite is created by choosing existing and new tests related to the areas where fixes and enhancements have been added. These test cases will also be prioritized based on the risk and importance of functionalities.
This is a testing approach where the features are tested based on their significance and influence on the overall software's functionality. The testing team will review the software's core features and ensure they are thoroughly tested.

The idea behind this technique is to ensure that the most important parts of the application have not been affected. However, it is still not a very efficient technique because it doesn’t focus on areas that were changed and requires much retesting on things that normally may not have been changed since they were last tested.

The Role of Automation in Regression Testing

When it comes to test automation, it is important to consider the test automation pyramid. This states that the bulk of the tests should be the unit tests, which are faster to run and, therefore, can identify defects quicker. Then there are the integration tests (or API tests), fewer in number but still represent a large number of tests to execute.

At the top layer, the UI end-to-end tests take the longest to run and should be fewer than the other levels.

By using automated test scripts, the entire regression process can be optimized. Test cases run faster, and bugs are identified quickly, with very little human intervention. The automated tests can run each time changes are made to the source code, and based on the test results, the testers can learn which areas are more affected and dig deeper into those areas with their manual testing.

Exploratory testing is always a great way to complement automation because it is a type of testing that cannot be automated, and the testers’ experience can bring a lot of value by identifying more uncommon scenarios.

Regression Testing Tools

The development team usually handles the first two layers of the pyramid, so in this section, we’ll explore some of the most popular UI automation tools that can help automate the testing process.

An open source tool for automating browsers, commonly used for test automation for web applications.

It’s available in multiple programming languages, including Java, Python, JavaScript, and C#, and works on all operating systems and common browsers. However, the testers who create the scripts must have coding knowledge.
Appium is the mobile equivalent of Selenium - a testing framework designed for testing mobile apps.

It’s also available in several programming languages and works on both Android and iOS.
Also an open source tool, JMeter can be used for functional testing, but it’s especially powerful for its performance testing capabilities.

It’s a great tool for when you need to perform load or stress testing on your application and compare the results (with the ones before the code changes) to see if performance has been impacted in any way.
Katalon is a tool for software testing on web, mobile, API, and desktop applications.

It also provides record-and-playback functionalities, so it works well in teams where the testers are not necessarily coders at the same time

Of course, the list can be expanded because there are many available automated testing tools on the market, and the one you choose will depend on the specific needs of the project and team.

Implementation Challenges 

Although the regression testing process is an integral part of the development cycle, it does come with challenges.

  • Time constraints: Time is probably the most common challenge with regression testing. Because the regression suite becomes bigger and bigger as new modules are added to the code, it can take up a lot of time, which the team may not always have. More time spent on regression can also increase costs.
  • Maintenance: As the existing code changes to add new functionalities and improvements, the test cases should also be maintained. This applies to manual and automated tests because all the existing test scenarios should reflect the new requirements.
  • Prioritization: One of the most important steps of regression testing. The team has to make sure that, considering the time available for executing regression, they select the right test cases and scripts, to maximize test coverage while minimizing the test suite size.

The Impact of Efficient Regression Testing on Product Quality

Despite the challenges, when done right, regression testing has a great impact on software quality.

First, with regression, the team ensures that new bugs are not introduced after new functionalities are added to the application.

This has a cascading effect on the code quality and the overall quality of the system under test.

Fewer bugs in production also mean greater customer satisfaction and a better customer experience.


Regression testing is an integral part of the testing strategy of any successful development process. It helps ensure that newly added features and fixes do not impact the existing working code and that the system meets the standards to be released in production.

With test case prioritization done right and the help of automation tools, the regression process can be a very efficient way to minimize the risks of breaking something that previously worked. This, in turn, helps the end user have a good user experience.

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Andreea Draniceanu
By Andreea Draniceanu

Hi there! My name is Andreea, I’m a software test engineer based in Romania. I’ve been in the software industry for over 10 years. Currently my main focus is UI test automation with C#, but I love exploring all QA-related areas 😊