Which set of test types is most appropriate to verify the non-functional requirements of a client-server system?

The most appropriate set of test types to verify the non-functional requirements of a client-server system includes Performance, Load, and Stress testing.

Performance testing is essential because it evaluates how the system behaves under various conditions, ensuring that it meets predefined performance standards. This is critical for non-functional requirements, which often address aspects like response times and resource usage.

Load testing assesses the system's ability to handle expected user loads, which is crucial for understanding how the system performs under typical usage conditions. It helps identify performance bottlenecks and ensures that the system can manage the anticipated number of concurrent users without degradation of service.

Stress testing goes a step further by evaluating how the system performs under extreme conditions, such as peak loads or beyond its limits. This is vital for identifying potential points of failure and ensuring that the system can maintain functionality under stressful scenarios.

Together, these three testing types comprehensively address key non-functional requirements, ensuring not only that the system operates effectively under normal loads but also that it is robust enough to handle exceptional situations.