unit-testing-first-tests.js

function orderTotal(order) {
  return order.items.reduce((prev, cur) => cur.price * (cur.quantity || 1) + prev, 0)
}

if (orderTotal({
  items: [
    { 'name': 'Dragon candy', price: 2, quantity: 3 }
  ]
}) !== 6) {
  throw new Error('Check fail: Quantity')
}

if (orderTotal({
  items: [
    { 'name': 'Dragon candy', price: 3 }
  ]
}) !== 3) {
  throw new Error('Check fail: No quantity specified')
}

if (orderTotal({
  items: [
    { name: 'Dragon food', price: 8, quantity: 1 },
    { name: 'Dragon cage (small)',  price: 800, quantity: 1 }
  ]
}) !== 808) {
  throw new Error('Check fail: Happy path (Example 1)')
}

if (orderTotal({
  items: [
    { name: 'Dragon collar', price: 20, quantity: 1 },
    { name: 'Dragon chew toy',  price: 40, quantity: 1 }
  ]
}) !== 60) {
  throw new Error('Check fail: Happy path (Example 2)')
}