compatibility testing

Difference Between Functional Testing and Regression Testing

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.

Difference Between Functional Testing and Regression testing

What Is Functional Testing?

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 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.

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.

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

Functional TestingRegression Testing
PurposeFunctional testing evaluates a software application’s functionality to ensure it performs as specified in the requirements. It verifies that the software accomplishes the tasks it’s designed for, checking features, user interactions, and data processing.Regression testing, on the other hand, is performed to ensure that recent code changes, enhancements, or fixes have not adversely affected existing functionalities. It confirms that the software’s previously tested features still work as expected after modifications.
ScopeFunctional testing focuses on testing specific features or functionalities in isolation. It is typically conducted during the initial development phase or when new features are added.Regression testing has a broader scope, covering the entire application or a significant portion of it. It is executed whenever there are code changes, even if those changes are unrelated to the feature being tested.
Test CasesFunctional testing is based on test cases that are designed to validate the intended functionality of a particular feature. These test cases are usually predefined and executed systematically.Regression testing often reuses existing test cases that have already been executed during functional testing. These test cases are employed to verify that no new defects have been introduced by recent code modifications.
FrequencyFunctional testing is typically conducted during specific phases of development, such as after feature implementation or before a major release.Regression testing is performed frequently throughout the development life cycle, particularly after code changes, to ensure that existing functionalities remain intact.
Time and Resource AllocationFunctional testing demands significant time and resources during the initial development phase and when new features are added or modified.Regression testing is ongoing and is often automated to save time and resources. Automation helps run regression tests quickly after each code change.
Test Case ExecutionIn Functional Testing, a fresh set of test cases and functionalities, which were never tested before, are executed. Test cases may also be re-executed when defects are identified, fixed, and assigned for re-test. If the defects are resolved, previously failed test cases are passed.In Regression Testing, test cases that were previously tested and passed are re-executed. These tests ensure that changes in the codebase have not negatively impacted previously validated features.

When Testing Is Required for Functional Testing and Regresstion 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 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

Techniques used in Functional Testing include:

Common techniques employed in Regression Testing are:

Read here – all about Functional Testing vs Integration Testing.

The Testing Process in Functional Testing Vs Regression 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.

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.


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.

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