// 1. Write implementation first
function calculateDiscount(price: number, customerType: string): number {
  if (customerType === 'premium') {
    return price * 0.2
  }
  if (customerType === 'regular') {
    return price * 0.1
  }
  return 0
}

// 2. Write test after (often skipped or superficial)
test('calculateDiscount works', () => {
  expect(calculateDiscount(100, 'premium')).toBe(20)
})
// Edge cases forgotten, API already locked in

// 1. Write failing test first (RED)
describe('calculateDiscount', () => {
  it('applies 20% discount for premium customers', () => {
    expect(calculateDiscount(100, 'premium')).toBe(20)
  })

  it('applies 10% discount for regular customers', () => {
    expect(calculateDiscount(100, 'regular')).toBe(10)
  })

  it('returns zero discount for unknown customer types', () => {
    expect(calculateDiscount(100, 'unknown')).toBe(0)
  })
})

// 2. Write minimal implementation to pass (GREEN)
function calculateDiscount(price: number, customerType: string): number {
  const discounts: Record<string, number> = { premium: 0.2, regular: 0.1 }
  return price * (discounts[customerType] ?? 0)
}