The use of these three terms is very common among technology professionals, who use them to describe an unexpected result during program execution or to refer to the cause of that result.
It’s important to have a clear understanding of the basic concepts of these three terms—error, bug, and failure—to grasp the difference between them, and to use them appropriately. It’s easy to confuse these terms in the area of software testing because they are closely related.
In software quality assurance, an error is a human action that produces an incorrect result; a defect, also known as a bug, is the manifestation of that error in the code; and a failure occurs when that defect becomes apparent while the system is in use.
A defect and a failure are related but distinct. A defect exists in the software, while a failure is the observable incorrect behavior that occurs when the defect is triggered during execution.
Relationship between Error, Defect, and Failure
These three concepts are closely related: an error can create one or more defects, and a defect can cause a failure. Human errors are inevitable in software development, which is why defects and failures must be anticipated and managed.
Remember that defects are not the only source of software failures; for example, unexpected changes to libraries or systems that many companies depend on can also result in failures.
