bug-fixer

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