问使用Rails进行敏捷Web开发4次迭代E3单元测试

EN

test 'duplicates must not be saved as a new line item' do
  # create cart and add one product
  cart = new_cart_with_one_product(:ruby)
  assert cart.save
  assert_equal 1, cart.line_items.count
  assert_equal 1, cart.line_items.find_by(
                   product_id: products(:ruby).id).quantity
  assert_equal 49.50, cart.total_price.to_f
  # ----------------------------------------------------------------


  # create a second (actually the same product) and add it to cart:
  item = products(:ruby)
  cart.add_product(item.id, item.price)
  assert cart.save
  assert_equal 1, cart.line_items.count, 'duplicate saved as new line'

  # test FAILS at the next two lines:
  assert_equal 2, cart.line_items.find_by(product_id: item.id).quantity,
             'quantity has not been increased'
  assert_equal 99.00, cart.total_price.to_f, 'total price is wrong'
end

class Cart < ActiveRecord::Base
  has_many:line_items, dependent: :destroy

  def add_product(product_id, product_price)
    current_item = line_items.find_by(product_id: product_id)

    if current_item
      current_item.quantity +=1
    else
      # create a new line_item
      current_item = line_items.build(product_id: product_id,
                                   price: product_price)
    end

    current_item
  end

  def total_price
    line_items.to_a.sum {|item| item.total_price }
  end
end