Software Testing | Error, Fault and Failure

The term error, fault and failure are often used interchangeable, but do have different meanings. In software, an error is usually a programmer action or omission that results in a fault. A fault is a software defect that causes a failure, and a failure is the unacceptable departure of a program operation from program requirements.

Failure is an event; fault is a state of the software caused by an error.

 

An error characterizes a particular state of a system, a failure is a particular event namely the transition from correct service delivery to incorrect service. An error may cause a fault to be injected into the application, and a fault may cause failure when the application is executed.

A single error may cause many faults. For example, a wrong algorithm is applied in multiple modules of the system and that causes multiple faults in the system. Similarly, a single fault may cause many failures in repeated executions. A faulty system would fail many times in repeated executions until the problem is fixed or patched. 

Error:

An Error is a human action or mistake when developing/using or operating a system or the software application. Human errors and mistakes introduce or inject faults into the system.

It is an outcome of human mistakes that leads to an inappropriate result from the working product. Error refers to the difference between the actual observed output and the correct expected output. Error is a discrepancy between a computed, observed or measured value/condition and the true specified or theoretically correct value/condition.

An error is a mistake, misconception, or misunderstanding on the part of a software developer. In the category of the developer, we include software engineers, programmers, analysts, and testers. For example, a developer may misunderstand a design notation, or a programmer might type a variable name incorrectly, leads to an Error. The error normally arises in software; it leads to a change in the functionality of the program.

Fault:

The result of an error being made is a fault. The fault is a condition that causes the software to fail in performing its required functionality. It is a symptom of an error in the software. It is something that is wrong in the software. Faults are also known as defects or bugs.

An incorrect step, process or data definition in a computer program causes the program to perform in an unintended or unanticipated manner. A fault is introduced into the software as the result of an error. It is an anomaly in the software that may cause it to behave incorrectly, and not according to its specification.

Failure:

Failures are caused by faults in the software. Failure is the inability of the program to perform its required function. As a result, the product is not able to perform the activity according to its specification. Failure occurs when fault is present in the system.