Tell me about the differences between functional and non-functional testing.

Functional testing verifies that the system does what it is supposed to do according to requirements. Non-functional testing assesses how the system performs its functions, evaluating characteristics such as performance, reliability, security, usability, etc.

Characteristic	Functional Testing	Non-Functional Testing
Goal	Verify compliance with requirements.	Verify system quality attributes.
What is tested	Functionality, operations, system behavior.	Performance, scalability, reliability, etc.
Requirements	Usually based on functional requirements.	Based on non-functional requirements (SLA, standards).
Types of testing	Unit, integration, system, acceptance, regression.	Load, stress, stability, security, usability, compatibility.
Who usually performs	Developers (unit/integration), QA engineers, business analysts/users (acceptance).	QA engineers (performance, security specialists).
Metrics	Number of defects in functionality.	Response time, throughput, availability, resource consumption, vulnerabilities.
Example	Successful user login verification.	Page load time verification during load testing.