Difference Between Unit Tests and Functional Tests

The article focuses on discussing the differences between Unit Testing and Functional Testing. The following topics will be discussed here:

1. What is Unit Testing?
2. What is Functional Testing?
3. Unit Testing vs Functional Testing

Let’s start discussing each of these topics in detail.

What is Unit Testing?

Unit Testing includes the testing of each unit or an individual component of the software application.  The main aim behind unit testing is to ensure that each unit or individual component is working as expected. 

• Unit Testing breaks the source code into various units and validates that every unit is working the right way. 
• In this way, early bugs and their fixes can be detected in the development cycle. 
• Also, it helps the developers to have a basic understanding of every unit, which also enables them to make modifications faster.

What is Functional Testing?

Functional Testing is the testing of the system to validate that the software system will work efficiently as per the functional requirements. The main aim of functional testing is to verify that each function works properly against the functional requirements and specifications.

• In functional tests, each functionality of the software application is tested by providing an appropriate test input and checking whether the output is as expected. 
• It helps to find defects in the system that the developers might have missed during the application development, and also it provides information about the quality of the output data.

Unit Testing vs Functional Testing

Both Unit Tests and Functional Tests are done to identify defects, prevent them and thus, deliver a quality product. Below are the differences between Unit Testing and Functional Testing.

Factors	Unit Testing	Functional Testing
Purpose	The primary purpose behind the unit tests is to verify that individual modules are working properly.	The primary purpose behind the functional tests is to verify that the software application is working properly.
Written by	Unit tests are written by the developers	Functional tests are written by the testing team.
Performed during	Unit tests are performed during the software development cycle	Functional tests are performed during the level of application testing.
Testing Technique	White Box Testing Approach is used for unit testing and is usually done by developers.	Black Box Testing Approach is used for functional testing and is usually done by testers.
Errors	Performing unit tests are helpful for detecting early bugs/problems in the code	Performing functional tests are helpful for detecting defects in the functionality
Cost and maintenance	The cost and maintenance of doing unit testing are low.	The cost and maintenance of doing functional testing is high.
No. of test cases	The number of test cases is higher than functional testing.	The number of test cases is lower than unit testing.
Speed	It is faster than functional testing.	Functional testing is slow and quite complex.
Modifications	Modifications are done frequently in unit testing.	Low rates of modifications are needed for performing functional testing.
Perspective	Unit tests are written from the developer’s perspective to ensure that every individual component is working as it is expected from the developers’ code.	Unit tests are written from the users’ perspective to ensure that the software system is working as it is expected by the user
Testing tools	Some commonly used unit testing tools are – Jtest, NUnit, EMMA, and PHPUnit.	Some commonly used functional testing tools are – Selenium, QTP, SoapUI, and Watir.