Differences Between Functional and Non-Functional Testing

When it comes to software testing, two critical categories play a key role in ensuring the success of your application: functional testing and non-functional testing. While both types of testing are vital to the development process, they focus on different aspects of an application’s performance. 

Functional testing, which centers around validating the core functionality of an application, ensures that your software works as expected from the user’s perspective. 

In this blog, we’ll explore the differences between functional testing and non-functional testing, highlighting why both are crucial to delivering a high-quality, reliable product.

What is Functional Testing?

Functional Testing ensures that a software application operates as intended, meeting its specified requirements. This type of testing focuses on evaluating user interactions, features, and outputs to verify that the software functions correctly.

It is a subset of software testing where Quality Assurance (QA) professionals check that the software works according to the technical, business, and customer requirements. Functional testing is generally considered black-box testing, as it does not require knowledge of the internal workings of the software. Instead, each function of the application is tested against the corresponding requirements established during the planning and development stages.

The process involves feeding specific user input data into the system, monitoring the resulting output, and comparing actual results with the expected ones.

Here are some examples of functions tested in functional testing:

• Can users successfully log into the site/app with the correct credentials?
• When a user clicks the “Buy Now” button, does the interface direct them to the correct next page?
• If a user enters special characters in a field where they aren’t allowed, does the system display an error message and prevent further actions?

If any of these concepts are unclear, don't worry. We’ll also dive into the differences between functional and non-functional testing later in this article.

Scope of Functional Testing

Functional testing covers:

• Verifying that each function of the application works as intended based on business and technical requirements.
• Ensuring that the application provides the expected output for every business logic specification.
• Performing both positive tests (i.e., checking the ideal conditions) and negative tests (i.e., testing how the application behaves in non-ideal conditions to ensure it still functions correctly).

Types of Functional Testing

1. Unit Testing
   Unit testing involves developers creating and running tests for individual pieces of code before they are integrated into the larger system. Each unit test focuses on verifying a single component and serves as the foundation for more complex tests later in the development process.
2. Component Testing
   This type of testing isolates and evaluates a specific software module. Component testing usually requires more complex scripts than unit tests and ensures that different units within the same module work together effectively.
3. Integration Testing
   Once individual components are verified, they are integrated and tested as a whole. Integration testing checks how well different modules, possibly developed by different teams, function together. For modern software that uses microservices, thorough testing of module interactions is essential.
4. System Testing
   System testing evaluates the software as an entire integrated system to ensure that it meets all stakeholder requirements. This is often referred to as End-to-End (E2E) testing and involves testing the software in a simulated real-world environment to confirm it’s ready for actual use.
5. Regression Testing
   Regression testing ensures that new changes or updates do not negatively affect existing features. It’s triggered whenever the software undergoes modifications to confirm that no new issues arise in previously functioning parts.
6. Sanity Testing
   Sanity testing is conducted after bug fixes or new features have been added to verify that the changes haven’t disrupted key functionality. It ensures that the most recent updates are stable before further testing.
7. Smoke Testing
   Smoke testing, or "build verification testing," is performed after the build is completed to check that basic functions work. It serves as a final check before moving on to User Acceptance Testing (UAT) or releasing the software to production.

Example of a Functional Test

Imagine you are developing a food delivery app that allows users to place customized orders. A unit test would check if the "Customize Order" button correctly saves user preferences like extra toppings or special instructions.

For another feature, such as tracking the order status in real time, you would perform component testing, since multiple units like the restaurant system, delivery partner updates, and user interface must interact to show accurate information.

If the app also allows users to pay via different methods, such as credit cards, digital wallets, or cash on delivery, integration testing would be necessary to ensure these payment modules work together without errors.

By running these functional tests, you can ensure that each feature performs as intended and contributes to a smooth and reliable user experience.

Suggested Read: Automated Functional Testing: Types, Benefits, Best Practices and Tools

Now that we’ve covered functional testing, let's shift gears and explore non-functional testing, which focuses on aspects beyond core functionality.

What is Non-Functional Testing?

Non-Functional Testing evaluates various aspects of a software application that go beyond its core functionalities. While functional testing checks if the application works as intended, non-functional testing ensures the software meets important quality standards such as speed, security, and scalability.

As the name suggests, non-functional testing focuses on aspects of software that aren’t directly related to specific functions. These include performance, usability, stability, efficiency, maintainability, and portability. This type of testing ensures that the software provides the best possible user experience in a real-world environment.

Non-functional testing uses the Software Requirements Specification (SRS) documents, similar to functional testing, to create test scenarios, suites, and scripts. The ultimate goal is to optimize these non-functional aspects of the software to enhance its performance and reliability.

Scope of Non-Functional Testing

Non-functional testing covers:

• Identifying potential issues related to usability, maintainability, efficiency, stability, and portability.
• Minimizing the risk of bugs or user dissatisfaction that could arise once the software is in production.
• Improving mechanisms related to installation, configuration, management, and monitoring of the software.
• Establishing key metrics for gauging product success based on expected real-world usage.
• Contributing to internal or open-source repositories with knowledge about the software and the underlying technology.

Types of Non-Functional Testing

1. Performance Testing
   This test evaluates whether the software performs optimally under normal and peak conditions. Key factors include loading speed, crash rates, memory usage, latency, throughput, and CPU efficiency.

Pro Tip: Use Sahi Pro to automate performance benchmarks over time and generate comprehensive reports for consistent improvement tracking.

2. Load Testing
   Load testing assesses how the system performs under stress, simulating a large number of simultaneous users or transactions. This test ensures that the system can handle increased load without sacrificing stability or performance.
3. Security Testing
   Security testing identifies vulnerabilities in the software that could be exploited by malicious users. It includes scanning the system for gaps in design that could lead to data breaches, unauthorised access, or system manipulation.

Pro Tip: Integrate Sahi Pro with third-party security tools to automate both functional and security regression testing in one go.

4. Visual Testing
   Visual testing focuses on verifying that UI elements are displayed correctly across different browsers and devices. This ensures that the software’s visual output matches the intended design, including elements like font, colour, shape, and placement.

Pro Tip: Pair Sahi Pro’s browser compatibility testing with visual validation tools to catch pixel-level issues quickly.

5. Stress Testing
   Stress testing examines how the system behaves under extreme conditions, such as an overload of users or transactions. It aims to identify the system’s breaking points and measures how it recovers from failures.
6. Scalability Testing
   Scalability testing evaluates how well the software can handle increased loads or growing data volumes. It checks the system's ability to scale horizontally (adding more resources) or vertically (enhancing capacity) without compromising performance.
7. Responsive Testing
   Responsive testing ensures that the application or website functions correctly across various screen sizes and resolutions. It tests how the software performs on different devices, including desktops, tablets, and mobile phones, ensuring a seamless user experience across all platforms.

Pro Tip: Use Sahi Pro's cross-device testing to automate checks across virtual and real devices for true responsiveness.

Examples of Non-Functional Tests

1. eCommerce Application
   For an eCommerce app preparing for a major sales event like Black Friday, load tests, recovery tests, and volume tests are critical. These tests ensure the system can handle a significant surge in traffic without crashing or experiencing performance issues.
2. Mobile Compatibility
   If a new iPhone is released, responsive and portability tests are necessary to verify that the app functions properly on the new device, ensuring compatibility with the latest iOS version and adjusting for different screen sizes.
3. Visual Consistency
   For a website with a prominent green button that serves as a call-to-action, visual tests are needed to confirm that the button appears correctly on various browsers and devices, ensuring that it is visible, unobstructed, and positioned according to the design specifications.

Non-functional testing ensures that the software performs well under various conditions, providing users with a reliable and enjoyable experience while meeting business and technical requirements.

Also Read: Different Types of Manual Software Testing

Now that we've explored both testing types individually, let's compare them side by side to highlight their key differences and understand how they complement each other.

Difference Between Functional and Non-Functional Testing

Functional and non-functional testing are both essential parts of the software quality assurance process, but they serve different purposes.

Below is a detailed comparison between functional and non-functional testing to highlight their key differences:

Both functional and non-functional testing play integral roles in ensuring software quality. Functional testing ensures that the core features and functionalities work as expected, while non-functional testing addresses performance, usability, and other important quality standards that impact the overall user experience.

Conclusion

Functional and non-functional testing are both crucial for delivering a high-quality software application. Functional testing ensures that the core features of the software work as expected, while non-functional testing focuses on assessing the performance, usability, and overall user experience under varying conditions. 

Both types of testing work together to create a robust, reliable product that meets both technical and user expectations.

If you're looking to optimize your testing process and ensure top-notch quality for your software, consider partnering with experts like Sahi Pro. 

Sahi Pro offers powerful, intelligent automation solutions to help streamline functional and non-functional testing for your applications. 

Visit Sahi Pro today to learn more and elevate your testing strategy!

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