The goal of any software or application testing is to build a quality product. Unit testing and Functional testing are the foundation of the testing process. The main difference is between the two is:

  • Unit testing is performed by the developer during the development cycle, and
  • Functional testing is performed by the tester during the level of system testing.

There are many such differences which you will get to know through the blog. My goal is to help you understand the different aspects of unit testing and functional testing.

What Is Unit Testing?

Unit testing is a popular practice adopted by many organizations as it primarily helps to eliminate the risk of having a bug in codes.

As the name suggests, unit testing is a type of software testing where individual units or components are tested. The purpose is to validate each unit of the software code and check whether they are performing as expected.

The goal of unit testing is to break each part of the source code into the unit and check that each part works properly. It means that if any set of input is not functional, it should return an expected output.

The Prime Objective Of Unit Testing Is:

  •  To isolate a section of code.
  •  To verify the correctness of code.
  •  To test every function and procedure.
  •  To find early bugs and fix in the development cycle and to save costs.
  •  To help the developers to understand the code base and enable them to make changes quickly.
  •  To help for code reuse.

Advantages Of Unit Testing:

  • Unit Testing allows developers to learn about the functionality that a unit provides. It also tells you how to use it to gain a basic understanding of the unit API.
  • Unit testing allows the developer to refine code and make sure the module works properly.
  • Unit testing enables testing parts of the project without the dependency of others for completion.

What Is Functional Testing?

Functional testing is a software testing process that validates the software system against functional requirements. The purpose of Functional testing is to test each functionality of the software application, by providing apt input, output verification against the Functional requirements. In other words, functional testing is a type of testing whereby the system is tested against the function requirement/specification.

The Prime Objective Of Functional Testing Is:

  • Finding defects that the programmer may have missed while developing software.
  • To Gain confidence and provide information about the level of quality.
  • To prevent defects.
  • To ensure that the result meets the business and the user’s requirements

Advantages Of Functional Testing:

  • Functional testing is necessary for evaluating the performance and the functionality of a software application before we deliver it to the client.
  • It takes the user’s perspective into consideration, which allows the software development team to create test scenarios that represent the real-world use scenarios.
  • It allows the team to meet the requirements of the user as well as the client.
  • It helps improve actual system usage.
  • It enhances the quality of the software product.

Difference Between Unit Testing And Functional Testing

Factors Unit Testing Functional Testing
Definition And Purpose Testing individual modules Testing the functionality as per user requirements
Written by Developers Tester
Testing Techniques White-box testing Black box testing
Errors Code branches, Edge cases Software / Application
No. Of Test Cases Higher than another testing Lower than unit and integration testing
Cost And Maintains Low High
Changes Changes frequently Low rates of changes

What Is The Purpose Of Both The Testing Types?

Unit Testing

Unit testing is a software testing method by which individual units of code are tested separately. The purpose of unit testing is to separate the smallest testable parts of an API and verify if they function properly in isolation. A unit test can verify different behavioral aspects of the system under testing, but mainly it verifies that the system under testing produces the correct results.

From the developer’s perspective, the purpose of unit testing is to create a strong codebase at a cheap cost. Another important purpose of unit tests is to provide proper documentation for high-level testing, i.e., integration testing and functional testing.

Functional Testing

In functional testing, a tester is not worried about the core code, instead they need to verify the output based on the user requirements with the expected output.

The main objective of Functional Testing is to check the functionalities of the system. Functional tests check the entire software, its hardware, and networking infrastructure – from the front end to the back end database systems. They are also a form of integration testing that ensures that all components are working together, as expected.

Unlike unit tests, the functional tests don’t tell you about the errors or its location. It just tells you that something is broken. It could either be the test, the browser, or a race condition. There is no way to tell because functional tests follow end-to-end testing.

How Do Unit Testing And Functional Testing Improve Software Quality?

Unit Testing

Sometimes, the code that you write may be lengthy, and you might not remember it for long. And a few months down the line, if you wish to re-work with the code, you might end up breaking it. In such cases, the unit test helps you to capture your original code and fix it later. It also protects you against regression. The defects in codes are identified almost immediately, so there is less re-work and re-test.

Functional Testing

It ensures the application or system works as expected. Typically have thorough tests for ensuring the critical app’s functionality, such as user logins, signups, payment gateway, and all the critical user workflows all behave, as expected.

There are different types of functional testing, and each has its benefits. For example, Integration testing checks that all the integration is working together. Smoke testing checks the critical features of the build, saves time, and reduces regressions.

System testing validates or verifies the entire software/application in the context of real user scenarios. End-to-End tests increase test coverage and decrease the chance of risk associated with integrating new code into an application.


Developers and Testers need to differentiate between the objective and scope of Unit tests vs Functional tests. Because both the tests are used for different purposes, they aren’t interchangeable. Both tests have their advantages and limitations.

  •  Unit testing is fast and helps writing clean code, but doesn’t provide confidence that the application will work as expected. It helps us where the problem/error is in the code.
  • Functional testing is slow and complex, but it ensures that the system will work as per the requirements. It helps us identify the problem/defects in the functionality.

The primary goal of testing is to deliver a quality product. Now it’s our job to find the right balance between Unit testing and Functional testing.