Non-Functional Testing
Non-functional testing evaluates how well a system performs a function, rather than whether it performs it correctly — covering qualities like performance, security, usability, scalability, and reliability. It answers "how well does it work" where functional testing answers "does it work at all."
A system can pass every functional test — every feature does exactly what it's supposed to — and still fail badly on non-functional grounds: too slow under real load, insecure against basic attacks, or so confusing that users can't actually complete their goals. Both dimensions matter, and neither substitutes for the other.
The category covers a lot of ground, each with its own dedicated glossary of terms: performance testing, security testing, usability testing, accessibility testing, and compatibility testing are all non-functional testing disciplines, distinct from each other but united by testing quality attributes rather than feature correctness.
