When end-user-visible behavior deviates from the expected behavior, this situation is called what?

When end-user-visible behavior deviates from the expected behavior, this situation is referred to as a failure. In the context of software testing and development, a failure occurs when the software does not perform as intended or as specified, according to the expectations set during the requirement phase. This kind of issue is observable to the end-user and results in a tangible discrepancy between expected outcomes and actual performance.

The concept of failure is crucial to understanding software quality, as it reflects the consequences of other underlying issues such as bugs or faults within the system. While a fault refers to an incorrect piece of code that could potentially cause a failure, and a defect is a broader term often used interchangeably with fault, a failure specifically focuses on the manifestation of that problem in the user's experience.

By recognizing failure in relation to expected user outcomes, testers can prioritize their efforts in identifying the root causes, whether they're errors or faults, thereby improving software reliability and user satisfaction.