What is Regression Testing?


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Toluwani Folayan

October 18, 2023

How annoying is it when you want to make a seemingly harmless change in your software code, only to watch a cascade of bugs tumble like a house of cards? If you're a software developer, this scenario is all too familiar. The frustration, delays, and unexpected late-night coding marathons are all part of the package.

But what if we told you you could tackle these challenges with regression testing? Regression testing can be your secret weapon in the battle against unexpected software hiccups. Simply put, regression testing is the practice of retesting your software application after making changes or updates to ensure that new code modifications haven't introduced unintended bugs or broken existing functionality.

This article will explain the basics of regression testing. We will tell you when to perform regression testing, how to choose test cases for regression testing, and also guide you on how to get started.


What is Regression Testing?

Importance of Regression Testing in Agile

Types of Regression Testing

When to Perform Regression Testing

How to do Regression Testing in Software Testing

How to Choose Test Cases for Regression Testing

Regression Testing Vs. Retesting. What is the difference?


What is Regression Testing?  

Regression testing is a quality assurance practice in software development that ensures previously working functionalities of a software application remain intact after new changes or updates have been made. It involves retesting the modified and unaffected parts to identify potential issues or regressions.

To simplify, imagine you have a software program that is functioning correctly. Now, let's say you make some changes or add new features to the program. Regression testing helps ensure that these modifications do not introduce any unexpected bugs or cause previously functional parts of the program to stop working.

For example, let's consider a web application used for online shopping. Suppose the development team adds a new feature that allows users to sort products by price. To perform regression testing, the testers would test the new sorting functionality and retest other existing functionalities, such as adding items to the cart, updating user profiles, and processing payments. This comprehensive testing ensures that the new feature does not adversely affect the application's overall functionality.


Importance of Regression Testing in Agile  

Regression testing plays a crucial role in Agile development by ensuring the stability and reliability of software applications. It involves retesting previously developed and modified functionalities to identify any unintended changes or defects that may have been introduced during the development process.

In an Agile environment, where frequent iterations and updates are common, regression testing helps mitigate the risk of introducing new issues while implementing new features or fixing bugs. For instance, by running regression tests, teams can verify that the existing functionalities continue to work as expected, even after implementing changes.

Here are some more benefits of regression testing in Agile methodologies:

1. Preserving Code Integrity: In Agile, where frequent code changes are the norm, even minor adjustments can inadvertently disrupt previously functioning features. Regression testing acts as a safeguard, ensuring that these changes don't create a ripple effect of issues that could be costly and time-consuming to rectify.

2. Continuous Feedback Loops: Agile thrives on iterative development and quick releases. Teams can maintain a continuous feedback loop by integrating regression testing into the development process. This helps identify and rectify issues early on, preventing a buildup of broken code that could jeopardize the final product near its production date.

3. CI/CD Facilitation: Continuous Integration/Continuous Deployment (CI/CD) relies heavily on automated tests. Regression testing is pivotal in this process, allowing developers to continuously test and integrate new code without compromising software stability. This synergy between regression testing and CI/CD promotes efficiency and reliability.

4. Scope Expansion: Regression testing goes beyond the mere functionality of the software. It offers the opportunity to delve deeper into analysis, pinpointing optimization possibilities. For example, it can be used to find defects and uncover opportunities for enhancing the user experience (UX). This comprehensive approach adds value by addressing both technical and user-centric aspects.

5. Visual Bug Detection: Visual regression testing is a powerful tool to detect visual bugs caused by changes in the codebase. For instance, it can identify issues like non-clickable buttons or misaligned images resulting from internal code adjustments. Rather than manually inspecting each UI element across multiple devices and browsers, automated regression tests streamline the process, making it efficient and effective.

Types of Regression Testing

There are several types of regression testing, each serving a specific purpose. The types of regression testing include:

1. Unit Regression Testing: This type of testing focuses on verifying the individual units or components of the software to ensure that changes made to one unit do not affect the functionality of other units.

2. Partial Regression Testing: In this approach, only a subset of test cases is selected from the existing test suite based on the modified software areas. This helps save time and effort by retesting only the impacted areas.

Essentially, partial regression testing is employed to evaluate how changes made in one part of the software may affect other interconnected sections. The method aims to ensure the overall stability of software after specific modifications. It is also beneficial when you want to identify potential ripple effects and dependencies between different modules or components. Partial regression testing helps detect any unintended consequences of alterations in one part of the software in other related areas.

3. Full Regression Testing: As the name suggests, full regression testing involves executing the entire test suite to ensure all software functionalities work as expected after making changes. It provides comprehensive coverage but can be time-consuming.

Full regression testing is typically conducted before a significant release or after multiple substantial modifications have been implemented. The purpose of complete regression testing is to ensure that all aspects of the software function correctly, providing confidence in the software's overall quality and stability.

4. Selective Regression Testing: This approach involves selecting specific test cases from the existing test suite based on the impact analysis of the changes made. Here, only the relevant test cases are executed, reducing the time and effort required for testing.

The primary purpose of selective regression testing is to ensure that these specific modifications have not negatively impacted the software's functionality. It is particularly useful when you want to save time and resources by concentrating testing efforts on the areas that have been altered. Selective regression testing also helps maintain confidence in the reliability of recently adjusted features.

5. Retest-All Regression Testing: In this method, all the test cases from the existing test suite are executed, regardless of the impact analysis. This ensures that any unforeseen issues caused by the changes are identified and addressed.

Additionally, Retest all regression testing is utilized when previous regression tests fail to pinpoint the root causes of issues. It thoroughly examines all changes made to the software over its development history. The primary goal is to identify the underlying sources of problems that may have been missed in previous testing cycles. Retest all regression testing ensures that all adjustments made throughout the software's lifespan are thoroughly scrutinized.

6. Progressive Regression Testing:

Progressive regression testing is specifically designed to ensure that changes made in the software do not adversely affect components from older versions. This type of testing is vital for verifying that recent modifications do not compromise the functionality of established features. Progressive regression testing helps maintain compatibility and reliability across different software versions.

7. Corrective Regression Testing:

Corrective regression testing is performed when no modifications or updates have been made to the software's features. Its purpose is to confirm that the existing functionality continues to operate as expected. This type of testing is essential for maintaining the integrity of the software by verifying that previous features remain unaffected even when no new code changes are introduced.

When to Perform Regression Testing  

Regression testing is typically performed in various scenarios to ensure a software application's continued reliability and functionality. Here are a few circumstances of when to perform regression testing:

1. New Functionality Added:

When new features or modules are introduced, regression testing verifies that the newly added functionality works correctly without impacting existing features.

2. Change in Requirements:

After significant changes in system requirements, regression testing is conducted to ensure that these alterations have not adversely affected other system parts.

3. Defect Resolution:

Regression testing is applied when defects or bugs are fixed. It confirms that the changes made to resolve issues have not caused new problems in related features.

4. Performance Enhancement:

Following the resolution of performance issues, regression testing validates that the optimizations have not negatively impacted other aspects of the software's functionality.

5. Integration with External Systems:

Regression testing is essential whenever the software integrates with a new external system or third-party component to ensure seamless interaction without disrupting existing functionalities.

6. UI Changes:

Regression testing is performed when the User Interface (UI) alterations are made to verify that these changes do not disrupt the overall user experience or existing features.

7. Configuration Changes:

Changes in the software configuration may trigger regression testing to confirm that adjustments do not lead to unexpected issues.

8. New Software Version Release:

Before releasing a new software version, regression testing is conducted to thoroughly assess the entire application and ensure that new updates have not introduced defects or affected existing features.

How to Do Regression Testing in Software Testing  

1. Identify Source Code Changes Through Code Review Sessions:  

Building a strong regression test requires understanding the implications and risks of the most recent code change. This is why you need to conduct code review sessions to pinpoint the altered parts or modules and their effects on the current functionality. This can be accomplished by comparing the differences between the old and new code using a version control system, such as Git.

You can also achieve this by identifying and thoroughly debugging any issues or defects in the software code when you investigate reported problems and trace them back to their source within the code.

2. Prioritize test cases and affected points of interest:

Next, you want to organize a Quality Assurance (QA) team to discuss which test cases need to be prioritized by extensive testing or which need minimal testing. Here is a tip to help your QA team prioritize test cases. Always remember that the essential alterations should always be those that influence the application's basic functions or fundamentally affect how it functions. Also, setting priorities will become more crucial as the size of the codebase grows. Depending on how many there are, it could take months or an entire sprint to finish all the tests.

3. Establish the Entry and Exit Points:

After prioritization, the team can choose the necessary tests once they have agreed on which changes need to be looked at. In most cases, testing teams have several test suites available for execution, but they only need to run the necessary ones during each regression testing session.

Essentially, the team creates a step-by-step plan in this stage and prepares the appropriate testing environment for regression testing.  For future test management to succeed, it is also required to eliminate outdated test cases or test suites.

4.  Test Case Selection:

This step involves selecting a set of test cases that adequately cover the software's functionality. Only once the code changes are implemented do you need to decide which test cases should be part of the regression test suite. These test cases should represent various scenarios and cover all critical features. This means they must encompass both the modified sections of the code and any areas that might be indirectly affected by the changes.

How to Choose Test Cases for Regression Testing  

When it comes to choosing test cases for regression testing, it's important to be methodical and thorough. Here is a step-by-step process to help you make informed decisions:

  • Understand the Application: Begin by understanding the application or software system under test. Familiarize yourself with its features, functions, and overall behavior.
  • Identify High-Risk Areas: Analyze the application to identify high-risk areas that are prone to defects or have undergone recent changes. These can include critical functionalities, complex modules, or components with a history of issues.
  • Prioritize Test Cases: Prioritize your test cases based on their importance and impact on the application. Focus on critical functionalities and those that end users frequently use.
  • Relevance to Recent Changes: Consider the recent changes or updates made to the application. Test cases covering these changes should be included in your regression suite to prevent introducing new defects.
  • Coverage of Core Functionality: Ensure your test cases cover the application's core functionality. This means testing the fundamental features that are crucial for the application's proper functioning.
  • Boundary and Error Conditions: Include test cases focusing on boundary values and error conditions. These help uncover any issues related to data validation, input handling, or error recovery mechanisms.
  • Historical Defects: Review the history of defects that occurred in the past and ensure that the corresponding test cases are part of your regression suite. This helps verify if the fixes were effective and if the same issues have resurfaced.
  • Consider Compatibility: If the application runs on different platforms, browsers, or operating systems, consider including test cases that cover compatibility aspects. This ensures that the application works seamlessly across various environments.
  • Test Data Variation: Include test cases involving different test data sets. This helps validate how the application handles various data inputs, ensuring its robustness and reliability.
  • Automation Potential: Evaluate the test cases for automation potential. Identify repetitive or time-consuming test cases that can be automated to improve efficiency and reduce manual effort in future regression cycles.

5. Regression Testing techniques:

Regression testing techniques are a set of methods used to verify that changes or updates made to software do not cause unintended effects or "regressions" in previously tested functionality. These techniques ensure that the existing software features still work correctly after making modifications.

Here are the three major regression testing techniques:

  • Retest All:

This technique involves re-executing all the test cases from the existing test suite. While comprehensive, it can be resource-intensive and time-consuming, making it suitable for smaller projects or critical areas of larger projects.

  • Regression Test Selection:

Here, a subset of test cases is selected from the test suite based on their relevance to the modified code. These chosen test cases are executed to ensure that the code changes have not introduced new issues or disrupted existing functionality. Additionally, test cases are categorized into reusable (suitable for future regression cycles) and obsolete (not applicable for subsequent cycles).

  • Prioritization of Test Cases:

Test cases are prioritized based on various factors, including business impact, criticality of functionalities, and frequently used features. This prioritization assists in selecting the most important test cases for regression testing. By focusing on high-priority areas, you can efficiently reduce the size of the regression test suite.

6. Test Environment Setup:

Here, you want to set up a stable and consistent test environment that closely resembles the production environment. This includes configuring the hardware, software, and network settings required for testing.

This is because regular regression testing always requires access to test environments. Hence, environments must be reliable and test-ready due to the frequent development of new code to avoid interfering with the scheduled testing schedule. Additionally, a bad environment configuration can cause false positives and negatives, undetected flaws, and test failures for other reasons.

7. Test Data Preparation:

This involves preparing the necessary test data that will be used during regression testing. For example, it could include creating new data sets or modifying existing ones to reflect the changes made in the software.

After this, the next step is to execute the selected test cases in the test environment by running the test scripts, performing manual tests, and recording the results. These test cases can be programmed to execute regularly over the course of the entire development cycle.

QA teams can also exercise more quality control over the ongoing modifications to their application by using time-based test execution.

8. Regression Test Evaluation:

Regression Test Evaluation is a crucial step in the software testing process. It involves carefully analyzing the test results to identify any discrepancies or defects that may have been introduced due to recent changes made to the system. This evaluation aims to ensure that the changes have not negatively impacted the system's functionality.

Hence, it is important to document any identified defects with detailed information during the evaluation. This documentation should include steps to reproduce the issue and the expected behavior. By providing this information, you will enable the development team to understand and replicate the problem effectively.

To report the identified defects, it is recommended to use a defect tracking system or any other reporting mechanism defined by your organization. This ensures that all relevant details are captured, such as the severity and priority of the defect, along with supporting evidence. Effective defect reporting facilitates efficient resolution by providing clear information to the development team.

Once the defects have been reported, the development team needs to fix them

9. Retesting:

After the defects are fixed, retest the affected areas to validate that the fixes have resolved the issues successfully. Focus on the specific test cases related to the fixed defects and ensure that the software's overall functionality has not regressed.

10. Test Coverage Evaluation:

Evaluate the test coverage to ensure that all critical functionalities have been adequately tested. Here, you want to identify any gaps in the test coverage and create additional test cases if required.

11. Regression Test Suite Maintenance:

Maintain a regression test suite that includes the selected test cases for future regression testing cycles. Update the test suite as new features are added, or existing ones are modified to ensure comprehensive coverage.


Regression Testing Vs. Retesting. What is the Difference?  

The difference between regression testing and retesting is that regression testing is performed to verify that the changes made in the software do not introduce new defects or cause existing functionalities to fail. It involves rerunning previously executed test cases to ensure the modified code works as expected and does not negatively impact other system parts.

On the other hand, retesting is conducted to validate that the defects identified during earlier testing phases have been resolved successfully. It involves executing specific test cases that previously failed or encountered issues to confirm that the fixes implemented have resolved the problems.

Summarily, regression testing is different because it searches the application for unknown bugs, which may have occurred due to some change implemented.



Regression testing is a systematic process involving bug identification, code fixing, test case selection, and various techniques like retesting all cases, regression test selection, and prioritization. It serves as a crucial component of software maintenance, safeguarding against unintended consequences of software modifications while ensuring the continued reliability and performance of the application.


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