Test-first bug fixing

Enforce a disciplined bug-fixing workflow that prevents regression and parallelizes fix attempts.

Core workflow

When a bug is reported, follow these steps in order:

Phase 1: Reproduce and document

•Understand the bug — Gather details about expected vs actual behavior
•Identify the test location — Determine where tests live in the project (check for tests/, __tests__/, spec/, *.test.*, *.spec.* patterns)
•Write a failing test — Create a test that demonstrates the bug

Phase 2: Fix with subagents

•Launch fix subagents — Use the Task tool with subagent_type=general-purpose to attempt fixes
•Run the test — Verify the fix by running the specific test
•Iterate if needed — If test still fails, launch additional subagents with new approaches

Phase 3: Verify and complete

•Run full test suite — Ensure no regressions were introduced
•Report success — Confirm the bug is fixed with passing test as proof

Writing the failing test

Test naming convention

Name the test to describe the bug:

python

# Python (pytest)
def test_user_login_fails_when_email_has_uppercase():
    ...

# Python (unittest)
def test_should_handle_empty_input_without_crashing(self):
    ...

javascript

// JavaScript (Jest/Vitest)
it('should not crash when input array is empty', () => { ... });
test('handles special characters in username', () => { ... });

typescript

// TypeScript
describe('UserService', () => {
  it('returns null when user not found instead of throwing', () => { ... });
});

Test structure

Every bug reproduction test follows this pattern:

python

def test_bug_description():
    # 1. ARRANGE - Set up the conditions that trigger the bug
    input_data = create_problematic_input()

    # 2. ACT - Perform the action that causes the bug
    result = function_under_test(input_data)

    # 3. ASSERT - Verify the expected (correct) behavior
    assert result == expected_value  # This should FAIL initially

Finding the right test file

Check the project structure for existing test patterns:

bash

# Find test files
find . -name "*.test.*" -o -name "*.spec.*" -o -name "test_*.py" | head -20

# Find test directories
ls -la tests/ __tests__/ spec/ test/ 2>/dev/null

# Check package.json for test command
grep -A5 '"test"' package.json

Launching fix subagents

Use the Task tool to parallelize fix attempts:

code

Task tool parameters:
- subagent_type: "general-purpose"
- description: "Fix [bug description]"
- prompt: Include:
  1. The bug description
  2. The failing test location and contents
  3. Suspected cause (if known)
  4. Constraint: "Run the test to verify your fix works"

Parallel fix strategies

Launch multiple subagents with different approaches:

•Direct fix agent — Focus on the immediate code causing the bug
•Root cause agent — Investigate deeper architectural issues
•Edge case agent — Look for similar bugs in related code

When projects lack tests

If the project has no test infrastructure:

•Set up minimal test framework first
•Create the test file in a sensible location
•Document the test setup for future use

Quick test setup commands

bash

# Python
pip install pytest
mkdir -p tests && touch tests/__init__.py

# JavaScript/TypeScript
npm install --save-dev jest
# or
npm install --save-dev vitest

# Go
# Tests are built-in, create *_test.go files

Verifying the fix

After subagent reports completion:

bash

# Run the specific test
pytest tests/test_module.py::test_bug_description -v
npm test -- --grep "bug description"
go test -run TestBugDescription -v

# Run full suite to check for regressions
pytest
npm test
go test ./...

Example workflow

User reports: "The login function crashes when email has spaces"

Phase 1 — Write failing test:

python

# tests/test_auth.py
def test_login_handles_email_with_spaces():
    """Bug: Login crashes when email contains spaces"""
    auth = AuthService()

    # This should return an error, not crash
    result = auth.login("user @example.com", "password")

    assert result.success == False
    assert "invalid email" in result.error.lower()

Run test to confirm it fails:

bash

pytest tests/test_auth.py::test_login_handles_email_with_spaces -v
# Expected: FAILED (demonstrates the bug)

Phase 2 — Launch subagent:

code

Task tool:
- subagent_type: "general-purpose"
- description: "Fix email space crash"
- prompt: "Fix the login crash when email contains spaces.

  Bug: AuthService.login() crashes instead of returning error when email has spaces.

  Failing test: tests/test_auth.py::test_login_handles_email_with_spaces

  After fixing, run: pytest tests/test_auth.py::test_login_handles_email_with_spaces -v

  The test must pass to confirm the fix."

Phase 3 — Verify:

bash

# Specific test passes
pytest tests/test_auth.py::test_login_handles_email_with_spaces -v
# PASSED

# No regressions
pytest tests/test_auth.py -v
# All tests pass

Integration with hooks

The bug-report-detector hook in this plugin automatically:

•Detects when a user reports a bug
•Reminds Claude to follow the test-first workflow
•Blocks Edit/Write tools until a test file has been created or modified

Additional resources

Reference files

•references/test-frameworks.md — Framework-specific test patterns
•references/common-bugs.md — Common bug patterns and test strategies

Example files

•examples/python-bug-test.py — Python pytest example
•examples/js-bug-test.js — JavaScript Jest example

Scripts

•scripts/find-tests.sh — Locate test infrastructure in a project