TDD Workflow

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Overview

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What This Skill Provides

• TDD Cycle: The RED-GREEN-REFACTOR loop
• Three Laws of TDD: Core principles for test-first development
• RED Phase: Writing failing tests that define behavior
• GREEN Phase: Implementing minimal code to pass tests
• REFACTOR Phase: Improving code quality while keeping tests green
• Test Prioritization: Which tests to write first
• AI-Augmented TDD: Multi-agent patterns for TDD

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The TDD Cycle

🔴 RED → Write failing test
    ↓
🟢 GREEN → Write minimal code to pass
    ↓
🔵 REFACTOR → Improve code quality
    ↓
   Repeat...

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Three Laws of TDD

1. Write production code only to make a failing test pass
2. Write only enough test to demonstrate failure
3. Write only enough code to make the test pass

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Key Phases

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RED Phase Principles

• Test must fail first
• Test name describes expected behavior
• One assertion per test (ideally)

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GREEN Phase Principles

• Don’t write unneeded code
• Don’t optimize yet
• Pass the test, nothing more

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REFACTOR Phase Principles

• All tests must stay green
• Small incremental changes
• Commit after each refactor

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Use Cases

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When to Use TDD

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Example Scenarios

1. New Feature: “Build a user registration system using TDD”
2. Bug Fix: “Write a test that reproduces the bug, then fix it”
3. Refactoring: “Refactor this module with test coverage”
4. Complex Logic: “Implement rate limiting with TDD”

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Test Prioritization

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AAA Pattern

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Anti-Patterns to Avoid

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AI-Augmented TDD

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Multi-Agent Pattern

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Related Skills

• testing-patterns: General testing principles
• webapp-testing: E2E testing with Playwright
• clean-code: Code quality during refactoring
• code-review-checklist: Reviewing TDD code

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Which Agents Use This Skill

• test-engineer: Primary user for TDD methodology

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Workflow Example

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Step 1: RED

test('should calculate total price with tax', () => {
  expect(calculateTotal(100, 0.1)).toBe(110);
});
// ❌ Test fails - function doesn't exist

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Step 2: GREEN

function calculateTotal(price: number, tax: number) {
  return price + (price * tax);
}
// ✅ Test passes - minimal implementation

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Step 3: REFACTOR

function calculateTotal(price: number, taxRate: number) {
  const taxAmount = price * taxRate;
  return price + taxAmount;
}
// ✅ Tests still pass - improved clarity

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Tools Available

• Read, Write, Edit: For test and implementation files
• Glob, Grep: For finding test patterns
• Bash: For running tests in the cycle