What type of test is designed to measure how a system performs under unexpected conditions?

Stress testing is a crucial method used to evaluate how a system performs under extreme conditions or unexpected workloads. This type of testing involves subjecting the system to high levels of stress—whether that be increased data loads, concurrent user access, or other challenging scenarios—to determine its limits and identify any potential points of failure. By doing this, stress testing helps ensure that the system can handle real-world situations that exceed normal operational levels without crashing or becoming unresponsive.

In contrast, while smoke testing checks basic functionality and confirms that essential features work after a build, it doesn't focus on system limits. Performance testing assesses the system's speed and responsiveness under normal conditions but does not stress it beyond typical operational levels. Regression testing, on the other hand, verifies that new code changes do not negatively impact existing functionality but does not specifically measure performance under unexpected conditions. Therefore, stress testing is the appropriate choice for understanding how a system withstands worse-than-normal conditions and maintains its integrity under pressure.