Difference Between Functional Testing and Regression Testing

Testsigma Inc.
10 min readMay 7, 2024

Functional and regression testing are two essential aspects of software quality assurance, each serving distinct purposes in the software development life cycle. In this blog, we’ll explore the purpose, execution, necessity, techniques, processes, automation, and maintenance of these essential testing methods.

What Is Functional Testing?

Software testing is carried out to ensure the final delivered product meets the desired requirements. Validation to understand if we are building the software right and verification if we are building the right software are both done during the testing phase.

Classification of software testing is done in various ways:

1. Some call it as White Box and Black Box testing

2. Others may call it Functional, Non-Functional, Maintenance testing. Broadly all testing types can be categorized into 2 types of testing:

  • Functional
  • Non-functional

Functional testing is a type of black-box testing, which means the tester is not concerned with the underlying code. It is done to verify that each function/feature of the software application functions in conformance with the requirements specification.it checks and assures that the product designed by developers works as per requirement specified by stakeholders. It is not about user testing, it is about how each action module/ unit or feature should work. Functional testing is carried out with the help of test cases that are derived out of all possible scenarios, both negative and positive.

Functional testing is both static and dynamic. It’s always better if it starts at an initial level of product development. It checks:

  • missing functionalities
  • incorrect specification
  • if any interface errors persist
  • gap that exists during the requirements phase

A well derived functional testing leads to delivering a high-end product. It helps:

  • to produce a bug-free product/software.
  • to check and assure that all the requirements are developed and tested as desired.
  • assures safety and security.
  • to ensure the end-user satisfaction.
  • to ensure the proper working of all the functionalities of an application/software/product.
  • to ensure the proper working of all the functionalities of an application/software/product.
  • Improve the quality of the product and risks associated with the product/software are exponentially reduced.

Let’s look at a few examples of functional testing:

  • Verify that the back button on the page is navigating to the correct page
  • Verify that links are redirecting to the right pages.
  • Drop-down features should list correct values on click
  • Verify that the next button takes to the next page
  • Verify that a user is able to type characters into the text fields as defined in the data element sheet

Functional Regression Testing is to test the application once more after new features are added or modification is done in the existing application. It checks for the same features, flows, functionalities as it was done during the functional testing phase. It ensures that the application runs smooth as it was working earlier. The purpose of the testing while performing functional regression testing is to check if modification of the application has not led to code break. It checks for:

  • End to end flow works fine.
  • Output data received is correct or not.
  • Data flow between modules is as expected.

Non-functional testing is to test the application from non-functional aspects such as performance, usability, security, reliability, load, stress, etc. It is basically done on live scenarios usually to check how the system will perform when kept under such circumstances.

Read more details about types of functional testing.

What is Regression Testing?

Dictionary meaning of the word “regression” is “the return to a former or less developed state.” So, testing done with the aim of catching any regressions in an already tested functionality is called Regression Testing.

These regressions in the code can occur as a result of “bug fixes”, “new features added to the code” or “changing requirements”. The aim is to test all the code that could be impacted due to recent changes to ensure that no new bugs are introduced in an already tested functionality.

Difference Between Functional Testing and Regression testing

In this topic, we would be discussing the difference between both testing types with respect to various aspects.

When Testing Is Required

Functional Testing

Functional testing is required:

  • When a new system or application is being tested.
  • To verify that an application complies with its specifications and desired requirements.
  • To confirm that system and module integrations work seamlessly.
  • When examining the functionality of a system as a whole is necessary.
  • To understand the workflow of a system and its functions.
  • To ensure that end-to-end flows yield the expected output.

Regression Testing

Regression testing is performed when:

  • A change request (CR) is raised by the client, resulting in code changes.
  • Backend code is migrated to a different platform.
  • New features are added to the existing application.
  • Patch fixes are applied.
  • There is a change in the testing environment.
  • Critical bugs identified by testers during the testing phase are fixed by developers.
  • Major concerns regarding performance issues and crashes are addressed.
  • The UI of the application is altered for a better user experience.

Techniques Used in both functional Vs regression testing

Functional Testing

Techniques used in Functional Testing include:

  • Black Box Testing
  • System Integration Testing
  • White Box Testing
  • Interface Testing
  • Unit Testing
  • System Testing
  • Integration Testing
  • Acceptance Testing

Regression Testing

Common techniques employed in Regression Testing are:

  • Component-Based Testing
  • Aspect Testing
  • Database Testing
  • Web Application Testing

The Testing Process in Functional Testing Vs Regression Testing:

Functional Testing

The process of Functional Testing involves:

  • Identifying the functionality to be tested.
  • Raising data requests if necessary.
  • Running test cases.
  • Comparing the output with the expected outcome.
  • Marking test cases as failed if they do not meet requirements.
  • Creating test scenarios based on the requirements.
  • Converting test scenarios into test cases.
  • Raising defects and assigning them to developers if discrepancies are found.
  • Re-executing failed test cases once raised defects are fixed.

Regression Testing

The process of Regression Testing is different. It is conducted only when the existing application undergoes modification or new features are added. The activities involved include:

  • Identifying the modified parts.
  • Prioritizing test cases based on the risk associated with changes.
  • Selecting test cases based on the areas impacted by modifications.

Automation Feasibility of Functional Vs Regression Testing

For Functional Testing, test cases are initially executed manually. Once a feature is stable, these test cases can be automated. In Regression Testing, only stable test cases are executed manually or automatically, and they can be automated as needed.

Maintenance and Modification of Test Scripts

Functional test cases typically require less modification since they are focused on specific features. In contrast, regression suite test scripts require more maintenance because they cover overall functionality. This suite may contain old test cases, cases that test functionalities that have changed, new features, or removed features. Keeping the regression suite updated after each release is crucial to avoid automation script failures.

In conclusion, Functional and Regression Testing are vital components of software QA, serving distinct purposes in the software development lifecycle. Functional Testing ensures that individual features work as intended, while Regression Testing safeguards existing functionalities when changes are introduced. Understanding when and how to use each of these testing methods is key to delivering high-quality software.

Tools To Perform Functional Regression Testing

Below are a few tools that provide the best services in regards to the automation of the regression suite. Each has its unique features that help make the automation process smooth and easy to understand for people who are new to the world of automation.

  1. Testsigma: one of the finest tools available in the market that provides cloud-based test automation service. It allows users to write test scripts in plain English language which is as easy as writing manual test cases. It has inbuilt artificial intelligence which helps you suggest critical areas of the applications.

Key features/services provided: Supports all platforms(Web, Native & Desktop) and browsers. Tool provides service options to prioritize test cases, build multiple test suites, schedule and run automated regression tests for each build automatically, and generate comprehensive reports with the drill-down approach. The best part of this tool is that Coding skills are not required.

For an in-depth study about automated regression testing and its aspects, check out our automated regression testing guide.

2. Watir: Stands for web application testing in Ruby. It is an open-source Ruby library to automate tests for web browsers. It requires you to be well versed with the Ruby language, which is simple and easy to understand. It cannot be used to automate native applications.

Key features/services provided: Easy to interact with web elements, supports all browsers.

3. TestingWhiz: is a codeless automation testing tool, helps automation across all platforms. It executes and manages test cases effortlessly & efficiently. It permits users to verify the critical functionalities of their web applications and deliver efficient and effective web interfaces.

Key features/services provided: Multiple Browser Support, Image comparison, Mobile testing support, Integration with a bug tracking tool, Integration with Test Management Tools, Captcha automation, Risk-based Testing.

4. TimeShiftX: is a time shift regression testing service. It creates a virtual clock container that permits applications to travel in the past or future to help you perform temporary or date simulating testing.

Key features/services provided: Requires no environment reboots and reloads, Supports all platforms & operating systems, no Code modifications required, Compatible with application & database.

5. Appium: It is an open-source tool. It is a wrapper for selenium used for mobile testing. The automation test script can be run on physical devices or emulators.

Key features/services provided: Supports parallel test execution which helps reduce time and increases the efficiency of tests, supports all operating systems.

6. Katalon Studio: It is a free automation service provider tool. It has a dual interchangeable interface for creating test cases, a manual view for the less technical users and a script view for experienced testers. This tool requires basic knowledge of scripting.

Key features/services provided: Supports all platforms(Web, Native & Desktop) and browsers, script execution on multiple devices. It can be integrated with Git, Jenkins, qTest, and Jira.

7. TestComplete: It is an automated regression testing tool designed by Smart bear. It helps automate functional test scenarios and backend scenarios such as database testing. It can be used across all browsers, operating systems, and native applications. The automation tool demands you to have basic knowledge of coding.

Key features/services provided: Supports Database testing, Integrates with other tools, Object-driven testing, Data-driven testing, Keyword-driven testing, Development of custom extensions, supports all web browsers, Operating systems.

8. IBM Rational Functional Tester: Automation tool designed by IBM. This software provides services to automate functional, regression, GUI and data-driven testing

Key features/services provided: Supports visual editing, Test scripting, Earlier data detection, Integration with other software, Story testing, Data-driven testing

9. Selenium: It is an open-source web testing automation tool. It supports many third party libraries to build a robust automation framework.

Key features/services provided: Supports parallel test execution which helps reduce time and increases the efficiency of tests, can be integrated with frameworks like Ant and Maven for source code compilation.

10. Tosca: It is a model-based test automation tool, used widely across all platforms, and has embedded business intelligence. This tool automatically scans the AUT(Application Under Test) script and loads into the software with minimal manual steps. Business intelligence helps the tool in suggesting certain critical tests that help the team identify the trouble areas, and thus reducing the risk.

Key features/services provided: built-in artificial intelligence, supports interactive testing, supports all platforms and browsers.


In conclusion, understanding the clear distinctions between Functional Testing and Regression Testing is paramount in the realm of software quality assurance. Functional Testing focuses on validating whether an application performs its intended tasks in line with specified requirements. In contrast, Regression Testing is the safety net that ensures recent code changes do not compromise existing functionalities.

While Functional Testing scrutinizes individual features in isolation, Regression Testing casts a wider net, encompassing previously tested components. The choice of when to employ each method hinges on the specific needs of a project — the risk involved, time constraints, and the criticality of the modifications.

Both Functional Testing and Regression Testing are vital facets of a comprehensive testing strategy, working together to maintain the integrity and reliability of software in an ever-evolving development landscape.

Frequently Asked Questions

Is regression testing functional or nonfunctional?

Regression can be functional as well as nonfunctional. Functional Regression testing checks for change or modification in code, backend, or environment changes have not led to any failures in the functionality of an application. Whereas, Non-functional regression testing checks for any performance issue that may have resulted due to newly introduced changes or modifications in the application.

Full functional testing or regression testing which one to perform after change?

When there is a modification or addition of feature(s) to any existing product, Regression testing is Deciding between a full cycle of functional testing, and regression testing can be challenging when a product undergoes modifications or new feature additions. To make an informed choice, consider the risk involved, the impacted module, and the allocated testing time:

Scenario 1 (High Risk, Sufficient Time): If critical functionality has changed and time permits, opt for a full cycle of functional testing to ensure no impact on previously tested features.

Scenario 2 (High Risk, Limited Time): When time is short but the risk is high, run a regression suite along with the full functional cycle for the modified functionality.

Scenario 3 (Medium Risk, Sufficient Time): With ample time, run the entire functional test suite to boost confidence in the application.

Scenario 4 (Medium Risk, Limited Time): If time is scarce but certainty is essential, run the full regression suite and additional functional tests focusing on the modified functionality.

Scenario 5 (Low Risk): When risk is low, running the regression suite alone is typically sufficient.

Scenario 6 (Urgent Change, Limited Time): For urgent changes with immediate deployment and insufficient time, run only the Tier 1 cases from the regression suite, ensuring system stability.

The choice depends on risk assessment, time constraints, and the criticality of the modified functionality.



Testsigma Inc.

Testsigma is a completely cloud-based codeless test automation tool that lets you create stable and reliable tests for web, mobile & APIs — all from one place.