| name | bug-fixer |
| description | Identifies and fixes bugs systematically. Invoke when user reports an error, test failure, or unexpected behavior that needs debugging and fixing. |
Bug Fixer
This skill provides a systematic approach to identify and fix bugs.
Workflow
1. Analyze the Error
- Read the error message carefully
- Identify the affected code files and functions
- Determine if this is truly a bug or expected behavior
2. Verify the Bug
Before fixing, verify:
- Is the error reproducible?
- Is there a test case that demonstrates the bug?
- Is the error in the code or in the test/usage?
3. Find Root Cause
- Trace the error back to its source
- Use logging or debugging to understand the flow
- Identify the exact line/condition causing the issue
4. Write/Update Test Case
CRITICAL: Always write or update test cases BEFORE fixing the bug.
- Create a test that reproduces the bug (should fail)
- This ensures we understand the bug correctly
- Provides regression protection
5. Fix the Bug
- Make minimal changes to fix the issue
- Don't refactor or make unrelated changes
- Ensure the fix addresses the root cause
6. Verify the Fix
- Run the test case - it should now pass
- Run related tests to ensure no regression
- If tests fail, re-analyze and fix again
Example Workflow
User reports: "NullPointerException in UserService.getUser()"
1. Read UserService.getUser() and trace the null path
2. Check if null input is valid or should be rejected
3. Write test: testGetUserWithNullInputThrowsException()
4. Run test - confirm it fails
5. Add null check and throw IllegalArgumentException
6. Run test - confirm it passes
7. Run all UserService tests - confirm no regression
Important Guidelines
- Never skip the test case step - tests document the bug and prevent regression
- Fix the root cause, not just the symptom - a quick fix often leads to more bugs
- Keep changes minimal - don't refactor while fixing
- Document the fix - add comments explaining non-obvious fixes
