8 Functional Testing Types Explained With Detail

Functional Testing Types

Quick Summary: In the most straightforward and simple words, functional testing tests various aspects of an application, website, or system to guarantee that it is correctly doing what it should be. This blog will explain each functional testing types and when it should be performed during the software development life cycle.

In the software testing phase, functional testing is a process that brings considerable benefits to the software development process. When it is executed correctly, it grows communication between developers, analysts, and testers. The management team can check the development process of the whole project at any point in time by inspecting the passing or failing functional tests.

Ultimately, it makes the development process faster because well-communicated requirements result in less re-work. The tests also discover a more modular architecture with subsystems that have clear responsibilities.

Developers test each functionality of the software according to the business requirement, and that’s why it is called functional testing. In this blog, you will find the scope of different functional testing types, their importance, and when you need to perform them.


What is Functional testing?

Functional testing is a software testing type used to validate the software system, whether the function is working according to requirements/specifications. The primary aim of functional testing is to test every functionality of the software application by giving the input value and validating the actual output with the expected result.  Functional testing mainly contains black box testing, which is not related to the source code of the application/software.

This testing confirms user interface, database APIs, Client/Server communication, security, and other app features under test. The testing may be done either using automation testing or with manual testing by developers/testers.

What to test in functional testing?

The objective of functional testing is to confirm that the software system’s functionality works consistently with demand.

It primarily focuses on:

  • Basic Usability: Functional testing includes the usability testing of the software system. It checks whether or not a user will navigate freely without any problem/issues through screens.
  • Accessibility: Functional testing verifies the accessibility of the function.
  • Mainline function: It concentrates on testing all of the software features.
  • Error Condition: Functional testing is employed to examine the error condition. It checks whether or not the error message is displayed.

The complete process to perform functional testing

The complete process to perform functional testing


1. Unit Testing

Unit testing is one of the types of software testing where the smallest functional unit of code or software components is tested. The purpose is to endure that each unit of the software performs as expected.

Mostly, it is done by developers during the development phase (coding phase) of an application. Unit tests separate a section of code and validate its correctness. A unit can be a separate function, procedure, method, module, or object.

Unit testing is the first level of testing done before integration testing in SDLC, STLC, and V Model. It is a White Box testing technique mainly performed by the developers.

However, due to time crises or developers’ unwillingness to test, QA engineers may also perform unit testing.

It is performed during the beginning of the software development phase, which helps expose defects during the initial development phases. It can also assist in reducing the higher cost of fixing the shortcomings during the later stages of the STLC.

Developers can use different Tools used for Unit Testing, such as Junit, Jtest, JMockit, NUnit, etc.


2. Component Testing

Testing each component or module separately to verify its expected output is called component testing or module testing. It is performed by the tester/QA after unit testing.

There is a significant difference between unit testing and component testing. Developers do unit testing during the coding stage in a white-box format to check that program modules execute.

In contrast, component testing is done to verify individual parts or objects of the application by testers in a black-box format.

Component Testing

From the above image, Let’s see what all we can test in login component exclusively:

  • Testing the UI part (spelling mistakes, logos, alignment, formatting etc,) for usability and accessibility
  • To confirm performance, testing the Page loading
  • Trying SQL injection over the UI components to test the breach of security at a beginning stage.
  • Verify the login functionality with valid and invalid user authorizations


3. Smoke testing

Smoke testing is one of the most important software functional testing types. Smoke testing is done on the ‘new’ build submitted by the development team to the Testing/QA team to make sure if the basic functionalities/features are working or not.

It should be done after the release of each build—the test cases selected to cover the major functionality or component of the software system.

The main purpose is not to perform complete testing but to test the critical functionality/features of the system. There is no point in testing the other functionalities. Another name for Smoke testing is ‘build verification testing’.


Smoke testing is done when a new build is released. It is executed on the application to verify that all important end-to-end functionalities work.

The build is stable if it passes the smoke testing. The QA team performs functional testing for the new additional features/ functionality, then performs regression testing.

Conversely, if the smoke testing fails, the build is rejected and forwarded to the development team to repair the build problems and create a brand new build. Smoke testing is done after unit testing and before validation testing.


4. Integration Testing

Integration testing is performed to check individual components’ compatibility with other similar components. In other words, it’s performed to make sure that the modules work fine on an individual basis and don’t show bugs once integrated. It’s one of the most common functional testing types. The tests are fully automated.

Usually, developers build separate modules of the system/software simultaneously and don’t concentrate on others.

They perform intensive black and white box functional verification, normally called unit tests, on the individual modules/components.

It causes Data and functional commands to flow between individual modules, which means they must work as parts of an entire system instead of a separate component.

Integration Testing

Integration testing exposes problems with data formats, operation timing, API calls, database access, and user interface operation issues.

A part of integration testing which checks data transfers between two modules or components is known as Interface Testing.

Interface testing checks the correctness of data transfer, Web services, messages, calls, APIs, and connection strings between two components in the application. These Interfaces take input and deliver output without having a UI.

Interface Testing

In technical terms, interface testing benefits to determine that different functionality like data exchange between the various components in the system are happening according to the way they were planned to happen.


5. Regression Testing

After some improvements in functionality/feature or code fixes, there is a huge chance these updates may cause any unexpected behaviours.

Regression testing is executed to test that if any new changes by coders have not hampered any existing running functionality or any additional change or defect is not injected into the code.

The main objective is to identify any bugs that may have been unintentionally introduced into the existing build and ensure that previously removed bugs remain dead.

Regression Testing

There are many functional testing tools available that provide Regression Testing. Some of them are,

  • Selenium
  • IBM Rational Functional Tester.
  • Micro Focus Unified Functional Testing (UFT)
  • Sahi Pro
  • Watir
  • TestComplete
  • SilkTest
  • TimeShiftX


6. Sanity Testing

After receiving a new software build with few modifications in features, testers perform a sanity test instead of performing a full regression test suite. It verifies that the modifications have fixed the issues, and the fixes have generated no additional issues.

It is mainly done after smoke testing to verify that each significant functionality of an web/mobile app is working well, both individually and collectively while integrating with other components.

Sanity testing is a subgroup of regression testing. Most testers get confused between sanity testing and smoke testing. You can understand the primary difference by the below image.

Sanity testing

7. System Testing

System testing is performed by testers on a complete, integrated system to assess its compliance and correctness with the requirements specifications (Functional or System).

The software system is passed for system testing after the successful completion of the integration testing. System testing is performed by independent testers who have not been part of developing the program. It is performed in a real-life environment with real-life usage.

System Testing

System testing is crucial because it validates that the system meets the client’s functional, technical, and business needs. It is accomplished before the User acceptance testing in the Software testing life cycle (STLC).

8. User Acceptance Testing

UAT (User Acceptance testing) is the final phase of the software testing process. In user acceptance testing, real application users test the app to ensure that it can handle essential tasks in real-world scenarios. UAT is performed at the time of software/app delivery to clients as a final spot to check among all functional testing types.

UAT - User Acceptance Testing

From the first phase to the deployment phase, the software/app undergoes different types of testing by QA Team or by developers. The main aim of all the efforts is to deliver an excellent working product that satisfies all requirements set by users and the client’s expectations.

Teams may become so used to the app that they may turn into a victim of tunnel vision. They are fully attentive to workarounds and may skip certain circumstances which may be life-threatening for end users. Hence, UAT is of utmost importance.

UAT depends on the end-user stories and establishes how well it fulfills their needs. Clients now use the ‘test to break’ approach while performing User Acceptance Testing.  UAT is a real-life representation of how well your application/software works in day to day situations.



We believe that functional testing plays a vital role in transforming a client’s understanding of end user’s requirements into applications that meet their necessities. Releasing software with serious functional faults can lead to tragic consequences.

When you have implemented all the above functional testing types at the correct time during the development period, a smooth delivery of a quality product is guaranteed.

If you want to perform test automation within a limited time frame for your web application and mobile app, functional tests are the best bet.

At Smarsh Infotech, we have dedicated testers; contact us to know more about our software testing services.

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