tdd-workflow

# TDD Workflow

## Overview

This skill guides the implementation of features using Test-Driven Development (TDD) principles. TDD is a disciplined, framework-agnostic approach where tests are written before implementation code, ensuring comprehensive test coverage and driving clean, testable design.

## Core Principle

**Never write implementation code before a failing test exists for that behavior.**

## Red-Green-Refactor Cycle

### 1. Red Phase: Write a Failing Test

**Goal:** Express the expected behavior through a test that fails.

**Process:**
- Select one small, specific behavior from the requirements
- Write a descriptive test that clearly expresses the expected behavior
- Run the test to confirm it **fails** (red)
- The failure should be for the right reason (not a syntax error or missing dependency)

**Why it must fail first:** A test that passes before any implementation is written might be testing the wrong thing or not actually exercising the code.

### 2. Green Phase: Minimal Implementation

**Goal:** Make the test pass with the simplest possible implementation.

**Process:**
- Implement only the minimal code necessary to pass the failing test
- Resist the urge to add extra features or handle edge cases not yet covered by tests
- Focus on making it work, not making it perfect
- Run the test to confirm it **passes** (green)

**Key principle:** Write the simplest code that could possibly work. Even hardcoding values is acceptable if it makes the current test pass - subsequent tests will force generalization.

### 3. Refactor Phase: Improve Quality

**Goal:** Improve code quality while maintaining passing tests.

**Process:**
- Review both implementation and test code for improvements
- Remove duplication (DRY principle)
- Improve naming and clarity
- Extract methods or classes if responsibilities are growing
- Apply language-specific idioms and patterns
- Ensure tests remain readable and maintainable
- Run tests after each refactoring step to ensure they