Difference Between Functional and Non-Functional Testing
1. Functional Testing
Functional testing verifies whether the application behaves as expected by checking its functionalities against the specified requirements. It ensures that each feature works correctly and meets business needs.
- Focuses on testing user interactions, system inputs, and expected outputs.
- Validates functionalities such as login, payment processing, form submissions, and database operations.
- Performed using manual testing, automation tools like Selenium, or API testing tools like Postman.
- Example: Testing whether a banking app correctly transfers money between accounts when valid credentials are provided.
2. Non-Functional Testing
Non-functional testing evaluates aspects of the system that are not related to specific functionalities but impact the overall user experience and system performance. It ensures that the software is efficient, scalable, and secure.
- Focuses on performance, security, usability, and reliability.
- Tests how the system behaves under stress, security threats, or high traffic.
- Includes load testing, stress testing, security testing, and accessibility testing.
- Example: Checking if an e-commerce website can handle 10,000 users shopping simultaneously without crashing.
3. Key Differences
The primary distinction lies in their objectives: functional testing verifies what the system does, while non-functional testing ensures how well it does it.
- Functional testing is based on business requirements, whereas non-functional testing is based on quality attributes.
- Functional testing checks correctness, while non-functional testing checks efficiency and robustness.
- Functional tests are easier to automate, whereas non-functional tests often require specialised tools like JMeter (for performance testing) or OWASP ZAP (for security testing).
4. Importance of Both in Software Development
Both testing types are crucial to delivering high-quality software. Functional testing ensures correctness, while non-functional testing guarantees reliability and user satisfaction.
- Without functional testing, an application may not meet business objectives.
- Without non-functional testing, an application may fail under real-world conditions.
- A well-balanced testing strategy, combining both approaches, enhances software quality and user trust.
- Example: A ride-hailing app must functionally match riders and drivers (functional) while also ensuring low response time and seamless GPS tracking (non-functional).