Quick Comparison: Functional Testing vs Regression Testing

What is Functional Testing? 

Functional testing is the process of validating the functions of the features of the application. This test is done to check if the application’s features are working according to the software, without any bugs or issues. Every software has its requirements and functional testing makes sure that the application is integrated properly and working smoothly to fulfil the required tasks. Each function is compared to the corresponding requirement and it is checked whether the result is the same as it will be expected from the user’s end. The process of carrying out the process of functional testing, in a nutshell, is providing sample inputs, capturing resulting outputs, and verifying that actual outputs are the same as expected outputs. 

Examples of some functional testing are- 

1. Check whether users can successfully log in to the portal once they provide legitimate credentials. 
2. Check if the payment process is carried out smoothly. 
3. Make sure that the payment gateway shows a message of error if the user enters invalid card details.
4. Check if the new record is being added to the database under the name “add new record”. 

Functional testing is also known as “black-box testing” sometimes as it focuses on the specification of the application rather than the complex coding. This means that the tester only has to run tests on the program rather than the system. 

What is Regression Testing?

Regression testing is a process that always comes later than functional testing. The reason is that it is a software testing practice that validates if the application is still up and running smoothly after code changes, updates and improvements. 

Regression testing makes sure that the existing features are stable and functioning properly overall. Whenever a new modification or a code is integrated into the application, regression testing is done to check if the whole application is stable under continuous improvements. 

When should the regression testing be done? 

1. Whenever a new requirement is added to the application it should be carried out.
2. When a new function or feature is added. 
3. A particular codebase that solves defects is fixed. 
4. When the source code is optimized or altered to improve performance and user experience. 
5. When patch fixes are added to the application. 
6. When there are changes made in the configuration. 

Regression testing as stated above is the last step as it helps to validate the complete application as a whole. New changes and features cannot be launched before carrying out regression testing.

Now let’s see how these two types of tests are different from each other.  

Also read: Jest vs Jasmine

Differences Between Functional Testing And Regression Testing

Here are some differences between functional testing and regression testing:

1. The Aim of Testing

Functional testing checks whether the aim of the feature in the applications is aligned with the requirements of the software. It tests if the users are getting what they expected and it is done in the initial stage. On the other hand, regression testing is done in the later stages. It checks the stability and functionality of the application as a whole when any new feature or code is added, updated or improved. It validates that the system has no code breaks or bugs after updation. 

2. Aspects Covered

Functional testing covers the following aspects-

• Analysing customer requirements. 
• Input data testing.
• Gathering the expected results.
• Executing the test case.
• Comparison between actual result and expected result. 
• Comparing the test case result. 

Regression testing covers the following aspects-

• Adding anything new to the software or making configuration changes.
• Integrating new changes to the built. 
• Adding new features or updating the old ones.
• Changing the existing functions. 

3. The Test Case Which is Being Executed

The test group of functional testing consists of a fresh set of cases and functionalities. These cases have never been tested or checked before. The test cases are executed again when any defects or bugs rise in any requirement of the application. After that, the existing bugs are fixed and then carried forward for tests again. When these bugs pass the test, the test cases are integrated into the application. In short, during regression testing, the test cases are re-executed to ensure that the changes have not affected previously tested features. 

Also read: Cypress vs Selenium

4. Situations That Require The Testing

Functional testing is required when- 

• A new system has to be tested.
• An application is validated against its features and requirements.
• Checking that module and system integration is working just fine.
• The functioning of the system has to be examined as a whole.
• Determining the workflow of the system.
• Ensuring that end to end flows are giving results that are expected from the users. 

Whereas, regression testing is required when-

• A client raises a change request and subsequently, the whole codebase is changed. 
• The backend code is migrated to another platform. 
• A new feature or function is added to the application. 
• New patch fixes are added. 
• The testing environment is slightly changed. 
• Critical defects are fixed by a developer which was initially found by the tester. 
• The user interface of the application is upgraded to improve the user experience. 

5. Methodology Used

The methodologies used in functional testing are-

• Black box testing
• System integration testing
• White-box testing
• Interface testing
• Unit testing
• Integrating testing
• Acceptance testing

Whereas, the methodologies used in regression testing are-

• Component-based testing
• Aspect testing
• Database testing
• Web application testing

6. Procedure Used

The processes used for functional testing are-

• Figuring out the functions to be tested.
• Raising requests for data.
• Running the test cases.
• Comparing actual and yielded results.
• The test cases which do not meet the requirements fail.
• Then the scenarios based on expectations are created.
• Converting test scenarios to test cases and raising bugs to assign to the developer.
• Re-running the failed case. 

Whereas, the processes used in regression testing are- 

• Identifying modified parts.
• Prioritizing test cases based on risk and then testing it.
• Selecting test cases based on areas impacted because of modification.  

Some tools that are used for both functional testing and regression testing are Testsigma, Watir, TestingWhiz, Time ShiftX, Appium, KAtalon Studio, IBM Rational Functional Tester and Selenium. 

Also read: Retesting vs Regression Testing