Functional Testing VS Non Functional Testing – Key Differences

When it comes to software testing types, they can be broadly divided into Functional and Non Functional Testing. In this article, we will briefly introduce both testing types and try to understand the difference between functional and non functional testing!

Functional testing is a type of testing that focuses on evaluating the software’s functionality. This testing ensures that the software performs per the specifications and requirements outlined during the design phase. On the other hand, non functional testing evaluates the software’s non-functional aspects, such as performance, scalability, security, and usability.

Both types are important, and in this blog post, we’ll closely examine what makes each unique.

Functional Testing VS Non Functional Testing – Overview

Here are simple explanations for both testing types.

What is Functional and Non-Functional Testing?

Software tests are largely categorized into functional and non-functional tests, both of which are essential for the application’s real-world quality and performance.

Functional Testing

Functional tests focus on verifying that an application behaves in accordance with predetermined requirements. They focus on the application’s specific functions, to verify that each of them work exactly as operated.

Key attributes

• Tests the app’s business logic and user interactions.
• Validates the system’s input, output, and data processing flows.
• Checks that the application meets all functional requirements

Types of Functional Tests

• Unit Testing – Tests individual components or modules.
• Integration Testing – Checks the quality interactions between integrated modules.
• System Testing – Evaluates the system functionality as a whole.
• Acceptance Testing – Verifies that the system meets all business and end-user needs.
• Regression Testing – Checks if any code changes break existing functionalities.
• Smoke Testing – Quick checks to verify major functionalities after pushing new code.

Example of Functional Testing

Testing the payment feature of an e-commerce app by entering accurate and inaccurate information (amount, bank login credentials, etc.). This is done to evaluate system responses, and whether they serve customer and business needs.

Non-Functional Testing

Non-functional tests evaluate attributes of an application that do not relate to functionalities. Rather it focuses on verifying performance, security and usability.

Key attributes

• Examines system performance under different real-world conditions — performance, security, scalability, latency.
• Verifies that the system meets predetermined quality standards for security, scalability and performance.
• Seeks to uncover and eliminate bugs to optimize user experience.

Types of Non-Functional Testing:

• Performance Testing – Evaluates system speed, responsiveness, and stability.
• Load Testing – Gauges how the system handles a sudden spike in user activity.
• Stress Testing – Verifies system behavior under unpredictable end-user conditions.
• Security Testing – Checks the system’s ability to guard and defend against cyber threats and security threats.
• Usability Testing – Gauges how easy it is for end-users to actually use the application.
• Compatibility Testing – Checks if the system works equally well across different devices, browsers, and OSes.
• Recovery Testing – Verifies how the system recovers from crashes or failures.

Example of Non-Functional Testing:

Testing how a website responds to sudden increase in high user traffic, at expected and unexpected times.

Functional Testing Vs Non Functional Testing – Advantages

Let us look into the advantages .

Functional Testing Advantages

Functional testing offers a range of advantages that make it one of the most effective methods for ensuring software quality. Some of the key benefits include:

1. Complete coverage: Functional testing allows testers to evaluate whether an application meets all its stated requirements, giving developers and QA teams a detailed understanding of how well the software works.
2. Improved accuracy: By carrying out functional tests in a controlled environment, errors can be isolated and addressed before they cause major issues. This helps reduce debugging time and ensures that bugs are caught during the development process rather than after release.
3. Improved user experience: As functional testing focuses on ensuring that applications work as planned, it helps ensure users have positive experiences when using them. This includes ease of use, speed, responsiveness, and stability.

Functional testing thoroughly evaluates software performance across many areas and helps organizations build more reliable, high-quality products.

Non Functional Testing Advantages

1. The primary benefit of this testing is that it ensures the application’s reliability, scalability, and performance under different workloads and stress conditions.
2. It also identifies user experience issues such as compatibility, accessibility, usability, and security.
3. Performing this tests helps to identify weaknesses or areas for improvement in system components before they break down or become a bottleneck.
4. Conducting this tests lowers the risk of financial loss due to system failure or downtime caused by inadequate network connectivity or hardware dependencies.
5. Also, this results in better quality software with quicker releases and fewer post-release bugs, leading to happier customers and business owners.

Key Difference Between Functional Testing and Non Functional Testing

The below-given table will explain in detail a few criteria of the key differences.

Criteria	Functional Testing	Non-Functional Testing
Purpose	To test the functionality of the software application and ensure that it meets the specified requirements.	To test the non-functional aspects of the software application, such as performance, usability, security, and reliability.
Testing Techniques	Black box testing, White box testing, Unit testing, Integration testing, System testing, and Acceptance testing.	Load testing, Stress testing, Usability testing, and Security testing.
Automated Execution	Automate the tests using tools like Testsigma, Selenium, Appium etc	Automate the test using  tools like Apache JMeter, LoadRunner, LoadUI, SoapUI, WebLoad
Metrics	Number of features tested, Pass/Fail rate	Transaction success rate, Response time, Resource utilization rate
Execution	Tests are executed after the system is developed and is ready for testing.	Tests are executed throughout the development lifecycle, from early requirements gathering to the final stages of deployment and testing.
Focus area	Focuses on the system’s functionality, i.e., whether the system is meeting the requirements.	Focuses on the non-functional aspects of the system, such as performance, scalability, usability, security, and reliability.
Requirement	Based on functional requirements, which describe what the system should do.	Based on non-functional requirements, which describe how the system should perform.
Usage	Used to ensure that the system meets the functional requirements and is working as expected.	Used to ensure that the system meets the non-functional requirements and performs well in performance, scalability, usability, security, and reliability.
Objective	To find and fix defects in the system’s functionality.	To find and fix bottlenecks and performance issues in the system, improve the system’s usability, and ensure that the system is secure and reliable.
Manual testing	It can be executed manually, but automation is becoming more common.	For some types of testing, like performance and load testing, automated scripts are generally used.
Functionality	Tests the functional aspects of the system, such as adding a new customer, placing an order, or generating a report.	Tests the non-functional aspects of the system, such as the system’s response time under load, the number of concurrent users that the system can support, and the ease of use of the system’s user interface.
Example Test Case	Functional: Verify that a user can successfully add a new customer to the system.	Non-functional: Verify that the system can handle 100 concurrent users without crashing.
Testing Types	Unit testing, integration testing, system testing, and acceptance testing.	Performance testing, scalability testing, usability testing, security testing, and reliability testing.
How to perform	Steps for manual and automated functional tests are outlined here.	More details about performing non functional tests to be found here.

Functional Testing vs Non Functional Testing Examples

Let us take an example application and look at the examples.

Application: Image Uploader Functional Testing Test Cases:

1. Verify the Upload button functionality
2. Check allowed file types
3. Validate image size limitation
4. Test the drag-and-drop feature
5. Verify File name with extensions

Non-Functional Testing Test Cases:

1. Test responsiveness on various screen sizes
2. Verify application performance
3. Check the compatibility across web browsers
4. Measure Upload time for large files
5. Test the load tolerance capability of the application

Conclusion

So, whether you’re a developer, tester, or project manager, it’s important to remember the differences between functional and non functional testing to create high-quality software that meets the needs of your users.

Frequently Asked Questions

Is API testing functional or nonfunctional?

API testing is functional testing, which tests how well the API performs its intended functions.

Is UI testing functional or nonfunctional?

UI Testing, also called GUI Testing, is a process designed to test that the components of any software a user interacts with functions as expected. This is a functional testing.

Key difference between functional testing and non-functional testing

The primary difference between functional testing and non-functional testing lies in the object being tested.

• Functional Testing verifies what the system does by checking if it meets business and functional requirements.

Non-functional testing verifies how the system performs under different real-world conditions, focusing on performance, security, usability, and scalability.