Functional Testing Vs. Unit Testing: A Comparison of Their Definitions, Objectives & Advantages

Trung Tran

Trung Tran | 17/06/2022

Functional Testing Vs. Unit Testing: A Side-by-side Comparison

There are many pairs of software testing methods that are commonly hard to distinguish and often confused over each other, and one among those is unit testing and functional testing. To differentiate these two software testing types, we will have to delve into their definitions, objectives, and also benefits before coming to a unit testing vs. functional testing comparison.


First of all, the definition of each will indicate how they are basically distinct.

What Is Functional Testing?

It is one type of software testing process. Functional tests check the end-to-end functionality of a software, application, or system against the pre-determined functional requirements and specifications to see if it works as expected. A functional test can be manual testing or automated testing. Functional testing involves the black-box testing systems. technique, and it does not aim to verify the source code.

Functional testing is an umbrella term for various testing types, such as integration testing, system testing, regression testing, acceptance testing, component testing, smoke testing, sanity testing, API testing, UI testing, white-box testing, black-box testing, alpha testing, beta testing, production testing, and also unit testing. Each of them serves different purposes under the same bigger goal of testing the functionality. These functional testing types can be defined briefly as below:

  • Integration Testing: An integration test checks if different software modules can work together as a system.
  • Component Testing: In this software testing method, individual software components are tested separately.
  • System Testing: System testing validates an entire system to see whether it meets the specified requirements and can be delivered to customers.
  • Regression Testing: Regression testing checks if changes made in the code have not introduced any new bugs or regressions.
  • Acceptance Testing: Acceptance testing is performed by end-users or customers before signing off on the project.
  • Sanity Testing: Sanity testing is done to check if new changes have not introduced any bugs in the existing functionality and if the system is still stable.
  • Smoke Testing: Smoke testing checks if the critical functionalities of a software application are working properly or not.
  • API Testing: An API test verifies an API and checks if it meets expectations in terms of functionality, reliability, performance, and security.
  • UI Testing: UI tests validate the graphical user interface of a software application.
  • White-box Testing: The white-box testing technique looks into the internal structure of the code or program to test its functionality.
  • Black-box Testing: It is a testing technique that assesses the functionality of a piece of software without having any knowledge of its internal structures or code.
  • Alpha Testing: It is performed in the development environment by in-house software developers before releasing it for beta testing.
  • Beta Testing: Beta testing is done by end-users or customers after alpha testing to get feedback about the product before its release.
  • Production Testing: It is done to check if a new software application can handle the load and perform well in a live or production environment.

What Is Unit Testing?

A unit test is also a type of software testing process in which individual units of software, application, or system are tested in isolation. The ultimate goal of unit tests is to validate the source code to check whether the units perform as expected, and unit testing often involves the white-box testing/blog/black-box-and-white-box-software-testing/#:~:text=WHAT%20IS%20WHITE,and%20other%20problems. technique. The unit test and integration test are also mixed up, but they are actually distinctive. A unit test can be manual testing or automated testing but usually automated.


Both functional tests and unit tests are important in software or application testing processes, but they are quite different in their objectives.

Objectives of a Functional Test

  • This software testing method is conducted by testers at all testing levels in the software development process:
  • To verify the compliance of the software or application with the defined functional requirements.
  • To check whether the functionality of a software, application, or system meets the user requirements.
  • To validate that all features work as expected.
  • To detect and resolve defects early in the development cycle and prevent possible ones, securing the software quality.

Objectives of a Unit Test

Unit tests are often conducted in the development process by software developers or sometimes quality assurance teams. Normally, the developers write test cases and run them to check units of code to ensure they function properly. Unit testing is considered the first level of software testing before moving to integration tests:

  • To validate each testable unit of software, application, or system in isolation.
  • To verify the accuracy of source code.
  • To catch bugs and fix them as soon as possible in the development cycle.
  • To secure code quality.
  • To shorten the testing cycle and the debugging process whereby saving development and maintenance costs.
  • To enable code reuse.


Both unit testing and functional testing play an integral part in the development workflow, but the set of benefits they offer also varies.

Benefits of Functional Tests

  • Functional testing lets you assess the performance and functionality of a software, application, or system to secure the quality before release. This helps to improve the quality of the final outcome and the system usage.
  • Since functional tests focus on the user’s perspective, functional testers can create the test scenarios that best describe the real-user scenarios.
  • With functional tests, the software engineering team can cater to not only the developer’s perspective and pre-defined requirements but also the users’ requirements and expectations.

Benefits of Unit Tests

  • Unit testing lets software developers learn and comprehend the functionality provided by a unit, thereby gaining the basic knowledge about the unit API.
  • The unit test enables developers to refine code, making it more reliable and easier to understand. It also helps to guarantee the unit/module functions properly.
  • Unit tests facilitate checking parts of the project without relying on others to complete them.

The Difference Between Functional Testing & Unit Testing

We have gone through different aspects of unit testing and functional testing, and obviously, they are not interchangeable. But in order to emphasize their distinctive features, let’s look into the differentiating factors that set them apart in this detailed comparison:

  • About purpose, unit testing aims to check the individual units in isolation while functional testing verifies the functionality of a software/app/system to see if it works as expected.
  • Developers are the ones who write unit tests, whereas testers are the ones conducting functional tests.
  • Unit testing involves white-box testing. Functional testing, on the other hand, involves black-box testing.
  • Unit testing is often done at the start of the development. Unlike unit tests, functional tests are conducted only after building the functions.
  • Since unit testing is easier and simpler to write and execute, its cost is lower than functional testing.
  • Functional tests can be both manual and automated testing, while unit testing is usually automated.


PurposeTest individual units in isolation.Test the functionality as pre-defined requirements.
Test CoverageThe number of lines of codeThe number of requirements fulfilled.
Testing TechniqueWhite-box testing.Black-box testing.
TargetIndividual units/modulesFunctionality of a software/app/system
Written ByDevelopersQA testers and test engineers
ComplexityMore complicated to conduct.Simple and easy to conduct.
ChangesAt frequency.Not change much.
Number of Test CasesHigher than other testing types.Lower than the unit test and integration test.
Cost & MaintenanceLowHigh
When to UseAt the beginning of the development process.After building the features.
Programming LanguagesSame as the coding languages.Can use different programming languages.
AutomationUsually, automated.Both manual and automated testing.
Issues CoveredCode errors and edge cases.Functionality and performance.
ToolsJunit, NUnit, Mockito, TestNGSelenium, UFT, SahiPro

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