A tester enters an invalid date in a booking form and the system crashes. The bug — a flaw in the component, for example an incorrect validation statement or data definition — causes the component to fail to perform its required function. The tester records the bug in a defect report with steps to reproduce, and the developer fixes the cause. When the fix is retested and confirmed, the bug is closed.
Is a bug the same as a defect? Yes, in ISTQB terminology bug and defect are synonyms for a flaw in a component or system that can cause it to fail to perform its required function. Related terms: a fault is the state of the component when the flaw is present, and a failure is the observable deviation of the component from its expected behavior.
What is the difference between a bug, a fault, and a failure? A bug (defect) is the flaw itself. A fault is the incorrect state caused by the defect being present. A failure is the externally observable deviation from expected behavior when the fault is activated during execution.
Is every unexpected behavior a bug? Not necessarily. The behavior may be caused by a faulty environment, test data, or user action — or it may be a specification issue. Investigation is needed before labeling something a bug.
Why do testers use “defect” instead of “bug”? Because defect is the precise, specification-oriented term used in standards and exams. Bug is the informal everyday word for the same concept.
What should a good bug report contain? A clear title, steps to reproduce, expected versus actual results, environment details, severity and priority, and supporting evidence such as logs or screenshots.
