Difference between Error, Fault and Failure
Overview
In this tutorial, we will look at the differences between Error, Fault, and Failure. These are often misunderstood by beginners in Software Testing.
Error/Mistake
To Err is Human.
Error is the difference between a computed, observed, or measured value or condition
and the true specified, or theoretically correct value or condition.
In Software, an error is a human action or mistake when developing/using, or operating a system or software application. Human errors and mistakes introduce or inject faults into the system.
An Error is an action that produces an incorrect result. An incorrect human action results in faults being injected into the software program. Examples are misinterpretations, omissions, etc.
Fault
A fault is adjudged or hypothesized cause of System Error. An incorrect step, process, or data definition in a software application. System error is a system state that is liable to lead to failure. In normal language, software faults are usually referred to as “bugs” or “defects”.
Failures are caused by faults in the application. Therefore, it refers to an underlying condition within the software application that causes failures to occur.
Note: A high-level picture that doesn’t take system error into consideration.
Failure
The inability of the program to perform its required activity. As a result, the product is not able to perform the activity according to its specification. Failures refer to a behavioral deviation from the user requirement or the product specification. A failure occurs if the observed behavior of a system, or program, deviates from its intended behavior.
The flow
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.
On the other hand, the same failure may be caused by several faults. For example, an interface or interaction failure involving multiple faulty modules.
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