Bug
A bug is a flaw or fault in the software that causes it to behave incorrectly or produce an unexpected result, deviating from the expected behavior.
A bug answers: “Why is the software not behaving as expected?”
1. Definition
A bug is a flaw or fault in the software that causes it to behave incorrectly or produce an unexpected result, deviating from the expected behavior.
A bug answers: “Why is the software not behaving as expected?”
2. Bug vs Defect (Practical View)
- Bug and Defect are often used interchangeably
- Conceptually:
- Bug → Technical flaw in the software
- Defect → Gap between expected and actual behavior (testing perspective)
| Term | Perspective |
|---|---|
| Bug | Development-centric |
| Defect | Testing / Quality-centric |
3. How Bugs Are Introduced
- Coding mistakes
- Incorrect logic implementation
- Misunderstood requirements
- Missing validations
- Integration issues
- Configuration errors
4. Bug Lifecycle (High-Level)
- New
- Assigned
- Open
- Fixed
- Re-tested
- Closed / Reopened
(Detailed lifecycle usually covered separately.)
5. Types of Bugs
5.1 Functional Bugs
- Feature not working as intended
5.2 UI Bugs
- Alignment, layout, broken buttons
5.3 Logical Bugs
- Incorrect calculations or conditions
5.4 Performance Bugs
- Slowness, freezes, timeouts
5.5 Security Bugs
- Unauthorized access
- Data exposure
6. Severity of Bugs (Impact)
- Critical – System crash, data loss
- High – Major functionality broken
- Medium – Partial functionality issue
- Low – Minor cosmetic issue
7. Priority of Bugs (Urgency)
- P1 – Must fix immediately
- P2 – Fix before release
- P3 – Fix if time permits
- P4 – Can be deferred
8. Manual Tester’s Role
- Identify bugs during test execution
- Reproduce bugs consistently
- Report bugs clearly with evidence
- Assign correct severity
- Re-test after fixes
9. Real-Time Example
Bug: Submit button does nothing
- Expected: Form submitted successfully
- Actual: No response
This is a functional bug with high severity.
10. Common Mistakes
- Reporting bugs without clear steps
- Logging duplicate bugs
- Incorrect severity or priority
- Reporting bugs due to misunderstanding requirements
11. Interview-Ready Answers
Short answer:
A bug is a flaw in software that causes it to behave incorrectly.
Detailed answer:
A bug is an error or fault introduced during development that results in deviation from expected software behavior.
12. Key Takeaway
A bug is a technical manifestation of a quality problem, and effective bug reporting is critical for fast resolution.