tdd-workflow

# TDD Workflow Skill

Guidance for Test-Driven Development methodology.

## The Core Cycle

**RED → GREEN → REFACTOR** (repeat)

| Phase | Purpose | Actions | Verify |
|-------|---------|---------|--------|
| **RED** | Define expected behavior | Write test for ONE behavior, run test | Test FAILS |
| **GREEN** | Make it work | Write MINIMUM code to pass | Test PASSES |
| **REFACTOR** | Make it clean | Improve ONE thing at a time, run tests after each change | Tests stay GREEN |

## Phase 1: RED - Write Failing Test

**Purpose:** Define behavior before implementation.

**Actions:**
1. Create/open test file
2. Write test for ONE behavior
3. Run test
4. Verify FAILURE (if it passes, test is wrong)

**Common mistakes:** Tests pass immediately, testing implementation not behavior, writing too many tests at once

## Phase 2: GREEN - Make It Pass

**Purpose:** Write MINIMUM code to pass test.

**Actions:**
1. Implement just enough to pass
2. No extra features, no optimization
3. Run tests, verify PASS

**Common mistakes:** Over-engineering, adding untested features, "while I'm here" additions

## Phase 3: REFACTOR - Improve Quality

**Purpose:** Clean up while keeping tests green.

**Actions:**
1. Identify improvements: duplication, naming, complex logic, long functions
2. Make ONE change
3. Run tests
4. If green, continue. If red, undo.

**Checklist:** Extract methods, rename variables, remove duplication (DRY), simplify conditionals, add type safety

## Test Patterns

**Arrange-Act-Assert (AAA):**
1. Arrange: Set up test data
2. Act: Execute the behavior
3. Assert: Verify result

**Given-When-Then (BDD):** Structure nested describes for readability

## Coverage Commands

| Language | Command |
|----------|---------|
| JS/TS (Jest) | `npx jest --coverage` |
| JS/TS (Vitest) | `npx vitest run --coverage` |
| Python | `pytest --cov=src --cov-report=html` |
| Go | `go test -cover ./...` |

## Anti-Patterns to Avoid

1. **Test After:** Writing code first defeats TDD purpose
2.