What Is The Difference Between Functional Testing And Unit Testing?

Unit Testing and Functional Testing

Unit Testing Vs. Functional Testing: A Detailed Comparison

Software testing’s ultimate purpose is to provide a high-quality product. Unit testing and functional testing are considered the foundations of the testing process in software development. On the other hand, unit testing is done by developers, and testers do functional testing. There are numerous such distinctions, which you will learn about in this blog.

In this article:

  1. Unit Testing Vs. Functional Testing
  2. What Is Unit Testing?
  3. The Prime Objective Of Unit Testing Is:
  4. Advantages Of Unit Testing:
  5. What Is Functional Testing?
  6. The Prime Objective Of Functional Testing Is:
  7. Advantages Of Functional Testing:
  8. Difference Between Unit Testing And Functional Testing
  9. What Is The Purpose Of Both The Types of Testing?
  10. How Do Unit Testing And Functional Testing Improve Software Quality?
  11. When to perform functional testing and unit testing
  12. Type of testing technique: White-box or Black-box?
  13. The Purpose of Test Coverage for Unit and Functional testing is different
  14. Which one is complex in writing test cases?
  15. Keep Balance of both Functional Testing and Unit Testing
  16. Conclusion 

Unit Testing Vs. Functional Testing

unit testing and functional testing difference

What is the difference between functional testing and non-functional testing?

Any software application testing should aim to provide a high-quality product. The core of the testing process is unit and functional testing. The following is the key distinction between the two:

  1. The developer performs unit testing during the development cycle, and
  2. The tester performs functional testing during the level of system testing.

There are several differences which you will get to know through the blog.

Unit Testing

What Is Unit Testing?

  • Unit testing is a common practice embraced by many businesses since it helps to reduce the possibility of having a bug in the code.
  • Unit testing, as the name implies, is a type of software testing in which individual units or components are tested. The objective is to test and validate each unit of software code to ensure that it is working as planned.
  • Unit testing’s purpose is to break down each portion of the source code into a unit and verify that each part functions properly. It indicates that the program should produce the intended result if any set of inputs isn’t working.
The Prime Objective Of Unit Testing Is:
  • To isolate a code section.
  • To ensure that the code is correct.
  • To put each function and technique to the test.
  • To detect and correct bugs early in the development cycle, as well as to save expense.
  • To aid developers in comprehending the code base and allowing them to make changes rapidly.
  • To aid with code reuse.
Advantages Of Unit Testing:
  1. Developers can learn about a unit’s functionality by performing unit testing. It also explains how to utilize it to learn the basics of the unit API.
  2. Unit testing allows the developer to fine-tune the code and ensure that the module functions correctly.
  3. Unit testing will enable you to test pieces of a project without relying on others to finish it.

Functional Testing

What Is Functional Testing?

Functional testing is a software testing method for ensuring that a software system meets its functional requirements. Functional testing aims to verify that each function of a software program meets the functional requirements by providing appropriate input and output. In another way, functional testing is a sort of testing in which the system is put to the test against a function requirement specification.

The Prime Objective Of Functional Testing Is:
  • Detecting flaws in software that the programmer may have overlooked during development.
  • To build trust and convey information about the quality of the product.
  • To eliminate flaws.
  • To ensure that the end outcome satisfies both the business and the user’s needs.
Advantages Of Functional Testing:
  1. Before delivering a software product to a client, functional testing is required to assess its performance and functioning.
  2. It considers the user’s perspective/point of view, allowing the software development team to construct test scenarios that closely resemble real-world use scenarios.
  3. It enables the team to meet the needs of both the user and the client.
  4. It aids in the betterment of actual system usage/usability.
  5. It improves the software product’s quality.

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/ integration test
Cost And Maintains Low High
Changes Changes frequently Low rates of changes

What Is The Purpose Of Both The Testing Types?

The Purpose Of Both The Testing Types

Unit Testing

Individual units of code are tested individually/separately in unit testing, a software testing method. Unit testing aims to break down an API into its smallest testable components and see if they work properly in isolation. A unit test can verify a variety of features of the system under test, but it primarily ensures that the system generates the desired outcomes. From the developer’s perspective, the goal of unit testing is to deliver/construct a robust codebase at a low cost. Another key job of unit tests is to provide adequate documentation for high-level testing, such as integration test/testing  and functional testing.

Functional Testing

In functional testing, a tester is not concerned with the core code; instead, they must compare the expected output to the user requirements. The main goal of functional testing is to ensure that the system functions properly. From the front end to the back end database systems, functional tests examine the entire software, hardware, and networking architecture. They’re also a type of integration testing that guarantees that all of the components work together as they should. Functional tests, unlike unit tests, do not provide information about problems or their location. It just informs you that something is wrong. It might be a race condition, the test, or the browser. There’s no way to tell because functional tests follow end-to-end testing.

How Do Unit Testing And Functional Testing Improve Software Quality?

Unit Testing And Functional Testing Improve Software Quality

Unit Testing

It’s possible that the code you create will be lengthy, and you won’t remember it for long. And if you want to work with the code again in a few months, you can wind up breaking it. In such circumstances, a unit test can assist you in capturing your original code and later fixing it. It also shields you from regressing. Because code flaws are quickly recognized, there is less rework and re-testing.

Functional Testing

It guarantees that the program or system functions properly. Typically, extensive tests are performed to ensure that important app features, such as user logins, signups, payment gateways, and all critical user workflows work as planned. There are several types of functional testing, each with its own set of advantages. Integration testing, for example, ensures that all of the integrations are in sync. Smoke testing verifies the build’s important features, saves time, and minimizes regressions. In the context of real-world user scenarios, system testing checks or verifies the entire software/application. End-to-end tests boost test coverage while also lowering the risk of introducing new code into an application.

When to Perform Functional Testing and Unit Testing

Unit tests cannot replace functional testing. However, they should serve as a good foundation for the rest of your testing procedure. The best strategy is to begin developing your tests as soon as you begin writing your code. TDD (Test Driven Development) is a software development methodology that emphasizes developing tests before writing code. The advantages of writing unit tests will become apparent over time. For example, you can refactor your code, and the unit tests will warn you if anything is broken.

Integration testing is a sort of functional testing that follows after unit testing. When two modules interact with each other, functional testing begins. The functionality is then functionally tested by the testers. A unit test can be used to test a single function, while an integration test can be used to see how two sections interact. Functional testing is on another level entirely. While unit tests can be hundreds of pages long, functional testing should be minimum.

White box testing and Black box testing

Type of testing technique: White box or Black box?

In white-box testing techniques, test cases are created using an internal perspective of the system and programming skills. The execution path and data structure sensitization are two common white-box testing criteria. They’re also known as “branch testing,” “route testing,” and “data flow testing.” According to its definition and purpose, unit testing is a white box testing technique. Unit-test also sensitizes all of the execution pathways and data structures in the unit you’re testing, making it a white box test once more. On the other hand, functional testing is a black-box testing technique in which the software’s functionality is tested without looking at the internal code structure. It is carried out in accordance with user/business requirements, with the resultant output being compared to the expected output.

The Purpose of Test Coverage for Unit and Functional Testing is Different

One of the most essential metrics in software testing is test coverage. For both functional and unit testing, it serves a separate purpose. A test coverage tool maintains track of which sections of the code are executed and which are not. We can refer to it as code coverage in the context of unit testing. Developers may be confident that their entire project is well-developed and maintained with high code coverage. There’s also a widespread assumption that having a high code coverage increases the quality of the code. Code quality will decrease if unit tests are poorly written and have high test coverage.

Test coverage helps build traceability between requirements and test cases in functional testing. Functional Test Coverage should indicate which features have been completed, i.e. They meet the acceptance test requirements (user acceptance testing), and which ones are still being developed. This type of data is far more readily available to product owners than the amount of lines of code used.

Test-driven development (TDD)

Which one is complex in writing test cases?

We’ll see how difficult unit testing may be in a TDD setting. As you may be aware, TDD requires you to write unit tests before developing production code. Here, you must consider the code design in advance, based on the requirements. When the design isn’t obvious at the start and evolves as you go along, you’ll have to rerun your test, which is time-consuming. Algorithms that change regularly, for example, take too long. In this scenario, deferring unit testing is recommended until you have a better concept of the design.

TDD becomes quite difficult at this point, as it requires many abstractions like mock objects, programming to an interface, MVC/MVP patterns, etc. It necessitates an enormous deal of knowledge, and developers are often required to create more unit tests than actual code. Other dependencies and integrations must be dealt with in real-time circumstances, such as the user interface and database.

Unit testing becomes quite difficult from dependencies when testing simple code because these code units have a proclivity for gluing together and orchestrating interactions among other code units.  We can fake out all dependencies in unit testing, but functional testing is different. Testing a simple screen that loads test data from the network is an excellent example; it’ll fail every time you run it offline. Functional testing becomes more difficult in such cases.

The scope of QA jobs is substantially broader. Developers typically split their work between creating new features and addressing bugs. A significant percentage of the time is spent testing functionality that has already been released and is in use. While the majority of the effort in developing and creating test plans for this capability was put into previous versions, any new feature produced necessitates the creation of a test plan and ongoing maintenance of existing tests. One of the key aims for QA managers is to minimize this effort. Teams who succeed in building clear and repeatable tests reduce the time it takes to maintain them and reduce the time it takes to register for them.

Keep Balance of both Functional Testing and Unit Testing

Functional Testing and Unit Testing

There are no commonly accepted testing guides for balancing unit and functional tests. The amount of tests required for each project varies depending on the variables. However, you can make the best decision by considering numerous tests in light of the project requirements and determining whether they are producing the desired results. Over-reliance on functional testing can have a negative impact on the application’s quality. Software engineering has changed continuously over the years. However, one area where we haven’t made any progress, if not regressed, is Software Quality Assurance. This is because many businesses rely significantly on functional testing while neglecting unit testing.

Let’s look at how a heavy reliance on functional testing and a lack of unit testing degrades the quality of the app.

  • Functional testing occurs after the feature has been developed. Hence feedback is not provided early in the SDLC.
  • Unit tests can handle the majority of edge situations and a larger range of input and output. 
  • Due to time and expense constraints, it’s impossible to cover all edge situations with functional testing.
  • When developers do not undertake unit testing, the chances of defects appearing in the production are significant. I’ve noticed that testers and developers are working longer hours to resolve production issues. It takes a long time since functional tests are unable to pinpoint the exact location of the problem.
  • Without Unit Tests, it’s difficult to alter or refactor code since no one knows what would fail if a specific piece of code is modified. This frequently results in regression testing problems, as modifications damage existing functionality. A breaking test would warn the developer of an oncoming calamity if Unit Tests cover the same piece of code.

Every software development project has three major goals: feature accuracy, clean and maintainable code, and efficient workflow. To complete these objects and maintain a balance of unit and functional tests, you can provide a simple set of questions for a product manager.

Additional Information on Functional Testing and Unit Testing

More Information on Functional Testing and Unit Testing

The pyramid’s largest segment, Unit Tests, serves as a firm foundation. Unit tests are inexpensive because they are simple to write and run. Because there are so many unit tests, developers utilize various unit testing tools to automate them (automated testing), depending on the programming language and framework they employ. Popular unit testing tools for various languages include JUnit (Java framework), PHPUnit (PHP framework), NUnit (.Net framework), and others.


Developers and testers must understand the difference between unit and functional tests in terms of goal and scope. Both tests are not interchangeable because they are employed for different purposes. Both tests have their own set of benefits and drawbacks.

  • Unit testing is quick and aids in the construction of clean code, but it does not guarantee that the system will perform as planned (performance testing). It shows us where the bug is in the code.
  • Functional testing is time-consuming and difficult, but it assures that the system meets the requirements. It tells us what the issue is with the functionality.

Testing’s ultimate purpose is to create a high-quality product. It’s now up to you to strike the correct balance between the unit and functional testing.

Scroll to Top