Can you explain what is meant by non-functional testing and how it differs from functional testing?

Non-functional testing checks the characteristics of the system that are not related to specific functions but to the quality of the application's operation. This includes, for example, performance, security, usability, reliability, and scalability.

Functional testing, on the other hand, verifies that the system performs its functions according to requirements — for example, the correctness of button operations, accuracy of calculations, data processing.

Example:

• Functional: Verify that clicking the 'Send' button actually submits the form.
• Non-functional: Verify that the form is submitted in less than 2 seconds under normal load.

Thus, non-functional testing evaluates how the system works, while functional testing assesses what it does.