Thursday, 26 February 2026

Error, Defect (Bug), and Failure in Software Testing

 In software development, the terms error, defect/Bug, and failure are generally used together. Many people suppose these words mean the same thing, but actually they are different. Let’s understand them in simple words.


1. Error

An error is a human mistake made during the software development process. It happens when a developer, tester, or analyst does something wrong.

This could be:

  • Misunderstanding a requirement
  • Writing incorrect logic
  • Using a wrong formula
  • Making a typing mistake in the code

In simple words, an error is an incorrect human action.

For example, if a developer writes the wrong calculation formula in a banking application, that is an error.


2. Defect (Bug)

A defect (also called a bug) is the result of an error found in the software. When the code with an error is tested, and it does not behave as expected, the tester identifies and reports it as a defect.

In short:
An error is made by a human → when it is found in the software, it becomes a defect.

For example, if the banking application calculates interest incorrectly because of a wrong formula, the tester will report it as a defect.


3. Failure

A failure happens when the software does not perform as expected in real use. This usually occurs when a defect is not fixed and the software is released to customers.

In simple words, failure is when the system actually breaks or gives wrong output while running.

For example, if customers see wrong interest calculations in the live banking system, that is a failure.


Relationship Between Error, Defect, and Failure

The connection between them is very simple:

Error (human mistake) → Defect (problem in software) → Failure (problem experienced by user)

 








 

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