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Functional testing is a software testing practice that increases communication between test managers, test engineers, developers, and business analysts. The management can observe the progress of a project at any time by examining the functional tests. Eventually, this speeds the development processes because well-communicated requirements ensure faster releases. Functional tests also drive architecture with subsystems that have clearly stated responsibilities. A functional testing company follows a testing approach that evaluates all functions of applications to ensure all components operate according to the requirements.  Each function of the application is tested in-depth to verify that the output by each feature is as desired. Functional testers test all functions by feeding input and verifying the output to check how the system works. The functional test may also involve testing os the APIs, database, user interface, security, and functionality of the application under test (AUT). functional tests do not include factors such as structure, code, performance, and environmental factors.  The primary purpose of functional testing is to ensure the usability and accessibility of the functions as per the required specifications. It also verifies that an application will function properly for all the users.

Testing teams need to include functional testing and regression testing into their QA strategies. Functional testing should be a continuous process during the development lifecycle and through production. It aims at ensuring:

• Meeting the end-user requirements 
• App development goals are achieved
• Identification of incorrect specifications
• Looks for interface errors
• Fine more issues 
• Meeting the regulatory and compliance requirements 

Regression Testing 

Regression testing is a testing approach that ensures the existing features work after the new changes have been made to the code. It is a regular part of the software development process and is carried out by QA experts. Coders/programmers develop test scenarios and test the bits of code after they are written. These tests are a part of the process. So, before releasing the new version of the product, old test cases are run against new version to ensure the old functionality is intact. Regression tests can also selected partially or completely of the tests that have been already executed. It is necessary to run regression testing for the following reasons:

• Changes to the code are made due to changing requirements
• After fixing defects
• When performance issues are resolved 
• Major changes to an application 
• Configuration changes
• When new features are added to an application 
• Patch fixes 

Scope of Testing 

Functional testing has a limited scope as it is feature-specific. For instance, if a team builds a car that has a specific navigation feature, testers will test that the feature is able to locate the car on a map and guide the driver to any desired destination. 

On the contrary, regression testing is not feature-specific. It is performed after a bug has been fixed or modifications to a feature that has been made, or when a new feature is added to an existing software application. Let us take the example of the same navigation feature as discussed above. If the mechanic has fixed some issues, then regression testing will be performed. Let’s say the navigation feature was not switching on and the mechanic resolved the issue, testers will test that it not only works but also ensure that everything else in the car is working correctly. Regression testing involves end-to-end testing of a product whereas functional testing refers to testing if a single feature works. 

Basic Purpose 

Functional testing aims at testing if a certain feature of the application works. Whereas, regression testing addresses detailed concerns about a product such as every feature in an application is working fine, if a certain problem in the app is resolved, etc. The basic purpose of both types of testing is different which follows an entirely different testing approaches. 

Acceptance Criteria

Functional testing does not only test if a feature works, but it also tests if a feature works the way it is expected to. If a new feature is added to an application, it is not only meant to work, but to also work efficiently. This is known as the acceptance criteria of a feature and functional testing is to test that feature. 

Regression testing has to consider the acceptance criteria for several features instead of just the single feature that was added, updated, or fixed. This happens because when a new feature is implemented or a bug is fixed, the fix may affect another component of an application. Thus, the acceptance criteria for that feature will no longer be fulfilled and this can only be determined if a tester looks at the acceptance criteria for all features that are caused by the change. 

Why Consider Functional and Regression Testing?

QA teams use functional testing and regression testing to ensure the stability of a product. When the regression testing cycle is performed after a change is made in its code and new bugs are identified, the test engineers learn how a code change in one component of a product impacts the code in the other parts. It also helps engineers while they develop new features as they know that certain parts of the code depend on the other parts. 

For teams that are still figuring out which features depend on each other to deliver a functioning product is essential not when bugs are fixed, but when new features are implemented. The results from previous tests help teams to plan for future testing cycles and highlight areas that should be tested when a new feature is added. Regression testing has a wider scope as compared to functional testing processes. However, if a product has gone through different cycles, teams can estimate the impact of change and then plan to test further.