Difference between Error, Bug, Defect, Fault and Failure

In software testing, we often hear terms like error, bug, defect, fault, and failure used interchangeably, but they all have distinct meanings.

Let's understand them with examples:

1?? Error: Human mistakes are made in the code or design that lead to incorrect results. A developer mistypes a mathematical formula in the code.

2?? Bug: An error is found during testing before the product is released.Example: During testing, the login feature fails because of the incorrect formula in the code.

3?? Defect: The tester reported a discrepancy between expected and actual results in the software. Example: The tester logs a defect in the system because the login feature doesn't work as expected.

4?? Fault: A defect in the system’s code that, when executed, causes the system to behave unexpectedly. Example: The incorrect formula (fault) causes the application to miscalculate values.

5?? Failure: It occurs when the software doesn’t perform as required in the live environment due to an unresolved defect. Example: A user cannot log in because the defect wasn’t fixed before release.

Key Takeaway:

Error: A human mistake.Bug/Defect: Found during testing.Fault: An underlying issue in the code.Failure: This happens when the defect affects users in production.

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