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Difference Between Functional and Non Functional Testing

Difference in Functional and Non Functional Testing
Posted On: 13 February 2024

Functional vs non functional testing is often one of the most raging debates in the testing world. It is nearly impossible to separate and prioritize one over the other. Modern digital applications require both in the right dosage. Let’s learn more about the difference between functional and non functional testing.

What is Functional Testing?

Functional testing ensures that each function of a software program performs in accordance with the required definition. This testing mostly consists of black box testing and is not concerned with the application's source code.

Every system feature is tested by entering acceptable data, checking the output, and comparing the actual results to the predicted outcomes. This testing includes examining the User Interface, APIs, Database, security, client/server applications, and functionality of the Application Under Test. Testing can be done either manually or through automation.

What is Non-Functional Testing?

Non-functional testing examines non-functional characteristics of a software application, such as performance, usability, and reliability. It is expressly designed to verify a system's readiness using nonfunctional criteria that functional testing never addresses.

Non-functional testing is as important as functional testing and impacts client satisfaction.

Functional Testing Vs Non Functional Testing

Attribute Functional Testing Non-functional Testing
Area of Focus Validates the output of an application or software product against expected outcomes and requirements. Focuses on the internal behavior of an application, including its ability to withstand different operating conditions.
Types of Testing Includes unit testing, regression testing, integration testing, system testing, and acceptance testing. Comprises performance testing, load testing, security testing, stress testing, recovery testing, and volume testing.
Customer Perspective Focuses on meeting customer requirements. Validates the customer experience for the application, considering customer feedback critical for test case planning.
Automation End-to-end automation testing is possible but considered easier to manage with manual testing. Automation is more feasible and often preferred due to the ability to model expected experiences, making it cost-effective.
Cost of Testing Initially less expensive but becomes costly due to manual efforts in the long run. Offers the advantage of easy automation, saving significant costs in large projects.
Requirements Gathering Straightforward path to defining exact requirements to validate with the application. More complex and time-consuming due to the need for extensive industry knowledge and understanding of customer expectations.

Example of Functional and Non Functional Testing

While developing a new e-commerce web application - "ShopFast." It is designed to provide users with a seamless shopping experience. Series of tests are conducted to ensure the application meets both functional and non-functional requirements.

Functional Testing Example:

One of the core functionalities of "ShopFast" is the checkout process. In functional testing, we focus on this process to ensure it works as expected.

Test Scenarios:

  • Adding items to the cart: Users can select and add products to their shopping cart.
  • Applying discounts: The system correctly applies discount codes before finalizing the purchase.
  • Checkout process: The application successfully processes payment information and completes the order.

In each case, input specific data (e.g., product selection, discount code), and verify that the output matches expectations (e.g., cart total updates, discount applied, order confirmation received).

Non-Functional Testing Example:

Non-functional testing for the same e-commerce application focuses on how well the application performs and meets other operational criteria.

Key Areas:

  • Performance Testing: Simulating high traffic to ensure “ShopFast” can handle peak shopping periods without significant slowdowns. This involves testing the application’s response and load time under heavy user load.
  • Security Testing: Given the sensitive nature of transaction data, security testing identifies any vulnerabilities that could lead to data breaches.
  • Usability Testing: Ensures a positive user experience by evaluating the application’s interface for intuitiveness and ease of navigation.

By addressing both functional and non-functional aspects, it ensures "ShopFast" is capable of performing its intended functions. It also excels in delivering a superior user experience, maintaining high performance under stress, and safeguarding user data against threats. This comprehensive testing approach guarantees a robust, efficient, and user-friendly e-commerce platform ready to meet the demands of its users.


No software testing method is universal. It's too restrictive to state whether functional or non-functional is superior.

Non-functional testing is equally important as functional testing. Many teams prioritize non-functional testing less since it yields smaller improvements. If performance drops, a user may be annoyed but still use the software.

However, malfunctioning functionality may prevent consumers from using their desired functions. Functional tests are used by many software testing teams due to their quicker execution times and reduced cost.

Get in touch with us to explore how this automation exercise works. Enjoy a free trial of ACCELQ to see how your business can leverage better quality experiences from digital applications every time.

Suma Ganji

Senior Content Writer

Expertly navigating technical and UX writing, she crafts captivating content that hits the mark every time. With a keen SEO understanding, her work consistently resonates with readers while securing prime online visibility. When the day's work ends, you'll find her immersed in literary escapades in her quaint book house.

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