Arunkumar Khannur's Software Testing Knowledge Center
3.2 Mistakes, Bugs, and Failures

Software systems sometimes do not work correctly because of -
  • Errors, also referred to as mistakes
  • Bugs also referred to as defects or faults
  • Failures

An error or a mistake is an incorrect result produced because of a human action. Some examples of errors include- incorrect usage of software by users, bad architecture and design by architects and designers, bad programming by developers, inadequate testing by testers, wrong build using incorrect configuration items by a build team member.

A bug or defect or fault is a flaw that exists in a component or system that can cause the component or system to fail to perform its required function. A bug, if encountered during execution, may cause a failure of the component or system. Examples on bugs include- an incorrect statement; wrong data type; wrong mathematical formula in design document; or a missing functionality in the system. Failure is a deviation of the component or system from its expected delivery, service or result. Thus, errors or mistakes made by human beings in software development produce faults, bugs or defects in software design or code or system. If a code or system with bug is executed, the system may experience a failure.

Low defect containment in any constructed work products and products is an essential prerequisite to a quality software process. To manage defects, each software engineer must address defects where they are injected by removing them, by determining their causes and also learning to prevent the same causes to occur again in future through software process improvement.
Bugs can occur as a result of sporadic events or chronic events.

Bugs caused by sporadic events occur infrequently and difficult and very time consuming to address such errors. Usually cost in terms of expenditure is projected & tracked in such errors and when they occur they demand immediate attention to address them. Example: Field defects reported from the system that is operational.

Bugs caused by chronic events occur frequently and are part of routine exercise like review and testing of software development. They are less time to fix and cost is not tracked. Example: Defects reported as test findings and review findings.
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Arunkumar Khannur, Software Testing - Techniques and Applications, Published by Pearson Publications, 2011 (ISBN:978-81-317-5836-6; Pages:341 + xxii)
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