tdd-mastery

Imported from xenitv1/claude-code-maestro (skills/tdd-mastery/SKILL.md). Install upstream with npx skills add xenitv1/claude-code-maestro --skill tdd-mastery. Copyright stays with the author.

<domain_overview>

🧪 TDD MASTERY: THE IRON LAW

Philosophy: If you didn't watch the test fail, you don't know if it tests the right thing. TDD is not optional—it's the foundation of trustworthy code. TEST-FIRST INTEGRITY MANDATE (CRITICAL): Never write production code before a test exists and has been seen failing. AI-generated code often attempts to write implementation and tests simultaneously or implementation first. You MUST strictly adhere to the Red-Green-Refactor cycle. Any code submitted without a preceding failing test or that generates tests after the implementation must be rejected as "Legacy Code on Arrival".

🚨 THE IRON LAW

NO PRODUCTION CODE WITHOUT A FAILING TEST FIRST

Write code before the test? Delete it. Start over.

No exceptions:

• Don't keep it as "reference"
• Don't "adapt" it while writing tests
• Don't look at it
• Delete means delete

Implement fresh from tests. Period. </domain_overview> <core_workflow>

🔴 RED-GREEN-REFACTOR CYCLE

Phase 1: RED - Write Failing Test

Write one minimal test showing what should happen.

Good Example:

test('retries failed operations 3 times', async () => {
  let attempts = 0;
  const operation = () => {
    attempts++;
    if (attempts < 3) throw new Error('fail');
    return 'success';
  };

  const result = await retryOperation(operation);

  expect(result).toBe('success');
  expect(attempts).toBe(3);
});

Clear name, tests real behavior, one thing

Bad Example:

test('retry works', async () => {
  const mock = jest.fn()
    .mockRejectedValueOnce(new Error())
    .mockResolvedValueOnce('success');
  await retryOperation(mock);
  expect(mock).toHaveBeenCalledTimes(2);
});

Vague name, tests mock not code

Requirements:

• One behavior per test
• Clear, descriptive name
• Real code (mocks only if unavoidable)

Phase 2: VERIFY RED - Watch It Fail

MANDATORY. Never skip.

npm test path/to/test.test.ts
# or
pytest tests/path/test.py::test_name -v

Confirm:

• Test fails (not errors)
• Failure message is expected
• Fails because feature missing (not typos)

Test passes? You're testing existing behavior. Fix test.

Test errors? Fix error, re-run until it fails correctly.

Phase 3: GREEN - Minimal Code

Write simplest code to pass the test.

Good:

async function retryOperation<T>(fn: () => Promise<T>): Promise<T> {
  for (let i = 0; i < 3; i++) {
    try {
      return await fn();
    } catch (e) {
      if (i === 2) throw e;
    }
  }
  throw new Error('unreachable');
}

Just enough to pass

Bad:

async function retryOperation<T>(
  fn: () => Promise<T>,
  options?: {
    maxRetries?: number;
    backoff?: 'linear' | 'exponential';
    onRetry?: (attempt: number) => void;
  }
): Promise<T> {
  // YAGNI - You Aren't Gonna Need It
}

Over-engineered

Don't add features, refactor other code, or "improve" beyond the test.

Phase 4: VERIFY GREEN - Watch It Pass

MANDATORY.

npm test path/to/test.test.ts

Confirm:

• Test passes
• Other tests still pass
• Output pristine (no errors, warnings)

Test fails? Fix code, not test.

Other tests fail? Fix now.

Phase 5: REFACTOR - Clean Up

After green only:

• Remove duplication
• Improve names
• Extract helpers

Keep tests green. Don't add behavior.

Phase 6: COMMIT

git add tests/path/test.ts src/path/file.ts
git commit -m "feat: add specific feature with tests"

Repeat for next behavior.

</core_workflow>

<quality_standards>

📋 GOOD TEST QUALITIES

🚫 COMMON RATIONALIZATIONS (ALL INVALID)

🚨 RED FLAGS - STOP AND START OVER

If you catch yourself:

• Writing code before test
• Test passes immediately
• Can't explain why test failed
• Tests added "later"
• "Just this once"
• "I already manually tested it"
• "Keep as reference"
• "TDD is dogmatic, I'm being pragmatic"

ALL of these mean: Delete code. Start over with TDD.

</quality_standards>

<bug_fix_protocol>

🐛 BUG FIX WORKFLOW

Bug found? Write failing test reproducing it. Follow TDD cycle.

Example:

Bug: Empty email accepted

RED:
test('rejects empty email', async () => {
  const result = await submitForm({ email: '' });
  expect(result.error).toBe('Email required');
});

VERIFY RED:
$ npm test
FAIL: expected 'Email required', got undefined

GREEN:
function submitForm(data: FormData) {
  if (!data.email?.trim()) {
    return { error: 'Email required' };
  }
  // ...
}

VERIFY GREEN:
$ npm test
PASS

Never fix bugs without a test.

</bug_fix_protocol>

<integration_and_tooling>

🔗 RALPH WIGGUM INTEGRATION

When Ralph Wiggum is active:

1. Before ANY implementation: Write failing test first
2. Proactive Gate: Check edge cases BEFORE coding (use TDD to cover them)
3. Reflection Loop: After implementation, verify RED-GREEN was followed
4. Verification Matrix: Track test coverage for each feature

Ralph Wiggum will REJECT:

• Code without corresponding tests
• Tests that were written after code
• Tests that pass without implementation

✅ VERIFICATION CHECKLIST

Before marking work complete:

• Every new function/method has a test
• Watched each test fail before implementing
• Each test failed for expected reason (feature missing, not typo)
• Wrote minimal code to pass each test
• All tests pass
• Output pristine (no errors, warnings)
• Tests use real code (mocks only if unavoidable)
• Edge cases and errors covered

Can't check all boxes? You skipped TDD. Start over.

🛠️ TESTING INFRASTRUCTURE

Stack Detection & Tool Setup

Auto-detect project type and setup appropriate tools:

Test Coverage Rules

For every new function/component, generate:

• 1 Happy Path - Expected successful behavior
• 2 Edge Cases - Boundary conditions, invalid inputs
• 1 Error Case - Expected failure handling

Contract-First (MSW)

Rule: Every frontend-backend interaction MUST have an MSW handler.

// Example MSW handler
import { http, HttpResponse } from 'msw'

export const handlers = [
  http.get('/api/users/:id', ({ params }) => {
    return HttpResponse.json({
      id: params.id,
      name: 'Test User'
    })
  })
]

Benefit: Decouples frontend development from backend availability.

Ghost Inspector Protocol

AI must scan for "Untested Logic Slabs" (>20 lines without coverage) and flag them:

# Check coverage gaps
npm run test -- --coverage
# Look for files with <80% coverage

</integration_and_tooling>

<reference_and_audit>

📖 RELATED SKILLS

• @testing-anti-patterns.md - Common mock/test mistakes to avoid
• @clean-code - Code quality standards
• @verification-mastery - Evidence before completion claims
• @debug-mastery - When tests reveal bugs

🏁 FINAL RULE

Production code → test exists and failed first
Otherwise → not TDD

No exceptions without explicit user permission. </reference_and_audit>