A deviation from the specified or expected behavior that is visible to end-users is referred to as what?

The term that describes a deviation from the specified or expected behavior that is visible to end-users is a failure. In the context of software testing, a failure occurs when the software does not perform as intended in a way that is apparent to the user. This can be due to a fault or defect in the code, but the actual observable impact on the user experience is what defines it as a failure.

Failures are important in the context of testing because they directly affect user satisfaction and usability. Identifying and addressing failures ensures that the software behaves as users expect, which is critical for delivering a quality product.

In contrast, the other terms are related but have different meanings in the software development lifecycle. An error typically refers to a mistake made by a developer or tester, while a fault (or bug) refers to a specific problem in the code that can lead to a failure. A defect is often used interchangeably with these terms but generally refers to the broader category of discrepancies from expected functionality, which may or may not lead to a visible failure. Understanding these distinctions helps in better diagnosing issues within the software and prioritizing fixes based on their impact on end-users.