TDD Command

This command invokes the tdd-guide agent to enforce test-driven development methodology.

What This Command Does

1. Scaffold Interfaces - Define types/interfaces first
2. Generate Tests First - Write failing tests (RED)
3. Implement Minimal Code - Write just enough to pass (GREEN)
4. Refactor - Improve code while keeping tests green (REFACTOR)
5. Verify Coverage - Ensure 80%+ test coverage

When to Use

Use /tdd when:

• Implementing new features
• Adding new functions/components
• Fixing bugs (write test that reproduces bug first)
• Refactoring existing code
• Building critical business logic

How It Works

The tdd-guide agent will:

1. Define interfaces for inputs/outputs
2. Write tests that will FAIL (because code doesn't exist yet)
3. Run tests and verify they fail for the right reason
4. Write minimal implementation to make tests pass
5. Run tests and verify they pass
6. Refactor code while keeping tests green
7. Check coverage and add more tests if below 80%

TDD Cycle

RED → GREEN → REFACTOR → REPEAT

RED:      Write a failing test
GREEN:    Write minimal code to pass
REFACTOR: Improve code, keep tests passing
REPEAT:   Next feature/scenario

Example Usage

User: /tdd I need a function to calculate market liquidity score

Agent (tdd-guide):
# TDD Session: Market Liquidity Score Calculator

## Step 1: Define Interface (SCAFFOLD)

```typescript
// lib/liquidity.ts
export interface MarketData {
  totalVolume: number
  bidAskSpread: number
  activeTraders: number
  lastTradeTime: Date
}

export function calculateLiquidityScore(market: MarketData): number {
  // TODO: Implementation
  throw new Error('Not implemented')
}

Step 2: Write Failing Test (RED)

// lib/liquidity.test.ts
import { calculateLiquidityScore } from './liquidity'

describe('calculateLiquidityScore', () => {
  it('should return high score for liquid market', () => {
    const market = {
      totalVolume: 100000,
      bidAskSpread: 0.01,
      activeTraders: 500,
      lastTradeTime: new Date()
    }

    const score = calculateLiquidityScore(market)

    expect(score).toBeGreaterThan(80)
    expect(score).toBeLessThanOrEqual(100)
  })

  it('should return low score for illiquid market', () => {
    const market = {
      totalVolume: 100,
      bidAskSpread: 0.5,
      activeTraders: 2,
      lastTradeTime: new Date(Date.now() - 86400000) // 1 day ago
    }

    const score = calculateLiquidityScore(market)

    expect(score).toBeLessThan(30)
    expect(score).toBeGreaterThanOrEqual(0)
  })

  it('should handle edge case: zero volume', () => {
    const market = {
      totalVolume: 0,
      bidAskSpread: 0,
      activeTraders: 0,
      lastTradeTime: new Date()
    }

    const score = calculateLiquidityScore(market)

    expect(score).toBe(0)
  })
})

Step 3: Run Tests - Verify FAIL

npm test lib/liquidity.test.ts

FAIL lib/liquidity.test.ts
  ✕ should return high score for liquid market (2 ms)
    Error: Not implemented

1 test failed, 0 passed

Tests fail as expected. Ready to implement.

Step 4: Implement Minimal Code (GREEN)

// lib/liquidity.ts
export function calculateLiquidityScore(market: MarketData): number {
  // Handle zero volume edge case
  if (market.totalVolume === 0) {
    return 0
  }

  // Calculate component scores (0-100 scale)
  const volumeScore = Math.min(market.totalVolume / 1000, 100)
  const spreadScore = Math.max(100 - (market.bidAskSpread * 1000), 0)
  const traderScore = Math.min(market.activeTraders / 10, 100)

  // Recent activity bonus
  const hoursSinceLastTrade = (Date.now() - market.lastTradeTime.getTime()) / (1000 * 60 * 60)
  const recencyScore = Math.max(100 - (hoursSinceLastTrade * 10), 0)

  // Weighted average
  const score = (
    volumeScore * 0.4 +
    spreadScore * 0.3 +
    traderScore * 0.2 +
    recencyScore * 0.1
  )

  return Math.min(Math.max(score, 0), 100) // Clamp to 0-100
}

Step 5: Run Tests - Verify PASS

npm test lib/liquidity.test.ts

PASS lib/liquidity.test.ts
  ✓ should return high score for liquid market (3 ms)
  ✓ should return low score for illiquid market (2 ms)
  ✓ should handle edge case: zero volume (1 ms)

3 tests passed

All tests passing!

Step 6: Refactor (IMPROVE)

// lib/liquidity.ts - Refactored with constants and better readability
const WEIGHTS = {
  VOLUME: 0.4,
  SPREAD: 0.3,
  TRADERS: 0.2,
  RECENCY: 0.1,
} as const

const SCALE_FACTORS = {
  VOLUME: 1000,
  SPREAD: 1000,
  TRADERS: 10,
  RECENCY_PENALTY: 10,
} as const

function clamp(value: number, min: number, max: number): number {
  return Math.min(Math.max(value, min), max)
}

export function calculateLiquidityScore(market: MarketData): number {
  if (market.totalVolume === 0) return 0

  const volumeScore = Math.min(market.totalVolume / SCALE_FACTORS.VOLUME, 100)
  const spreadScore = clamp(100 - (market.bidAskSpread * SCALE_FACTORS.SPREAD), 0, 100)
  const traderScore = Math.min(market.activeTraders / SCALE_FACTORS.TRADERS, 100)

  const hoursSinceLastTrade = (Date.now() - market.lastTradeTime.getTime()) / (1000 * 60 * 60)
  const recencyScore = clamp(100 - (hoursSinceLastTrade * SCALE_FACTORS.RECENCY_PENALTY), 0, 100)

  const weightedScore =
    volumeScore * WEIGHTS.VOLUME +
    spreadScore * WEIGHTS.SPREAD +
    traderScore * WEIGHTS.TRADERS +
    recencyScore * WEIGHTS.RECENCY

  return clamp(weightedScore, 0, 100)
}

Step 7: Verify Tests Still Pass

npm test lib/liquidity.test.ts

PASS lib/liquidity.test.ts
  ✓ should return high score for liquid market (3 ms)
  ✓ should return low score for illiquid market (2 ms)
  ✓ should handle edge case: zero volume (1 ms)

3 tests passed

Refactoring complete, tests still passing!

Step 8: Check Coverage

npm test -- --coverage lib/liquidity.test.ts

File           | % Stmts | % Branch | % Funcs | % Lines
---------------|---------|----------|---------|--------
liquidity.ts   |   100   |   100    |   100   |   100

Coverage: 100% (Target: 80%)

TDD session complete!

## TDD Best Practices

**DO:**
- Write the test FIRST, before any implementation
- Run tests and verify they FAIL before implementing
- Write minimal code to make tests pass
- Refactor only after tests are green
- Add edge cases and error scenarios
- Aim for 80%+ coverage (100% for critical code)

**DON'T:**
- Write implementation before tests
- Skip running tests after each change
- Write too much code at once
- Ignore failing tests
- Test implementation details (test behavior)
- Mock everything (prefer integration tests)

## Test Types to Include

**Unit Tests** (Function-level):
- Happy path scenarios
- Edge cases (empty, null, max values)
- Error conditions
- Boundary values

**Integration Tests** (Component-level):
- API endpoints
- Database operations
- External service calls
- React components with hooks

**E2E Tests** (use `/e2e` command):
- Critical user flows
- Multi-step processes
- Full stack integration

## Coverage Requirements

- **80% minimum** for all code
- **100% required** for:
  - Financial calculations
  - Authentication logic
  - Security-critical code
  - Core business logic

## Important Notes

**MANDATORY**: Tests must be written BEFORE implementation. The TDD cycle is:

1. **RED** - Write failing test
2. **GREEN** - Implement to pass
3. **REFACTOR** - Improve code

Never skip the RED phase. Never write code before tests.

## Integration with Other Commands

- Use `/plan` first to understand what to build
- Use `/tdd` to implement with tests
- Use `/build-and-fix` if build errors occur
- Use `/code-review` to review implementation
- Use `/test-coverage` to verify coverage

## Related Agents

This command invokes the `tdd-guide` agent located at:
`~/.claude/agents/tdd-guide.md`

And can reference the `tdd-workflow` skill at:
`~/.claude/skills/tdd-workflow/`