describe '#total_price' do
  before(:each) do
    user = User.new(email: 'test1@example.com', password: 'test1234')
    price = 900
    @order = Order.new(user: user, total: price)
  end
  it 'does something' do
    @order.save
    expect(@order.total).to eql(900)
  end
end

1) Order Instance Methods #total_price does something
 Failure/Error: expect(@order.total).to eql(900)

   expected: 900
        got: 0.0

   (compared using eql?)

class Order < ApplicationRecord
  belongs_to :user, optional: true
  has_many :order_items
  before_save :update_total

  def total_price
    price = order_items.collect do |order_item|
      order_item.item_unit_price * order_item.quantity
    end
    price.sum
  end

  private

  def update_total
    self[:total] = total_price
  end
end

def total_price
    price = order_items.collect do |order_item|
      order_item.item_unit_price * order_item.quantity
    end
    price.sum
end

describe '#total_price' do
  before(:each) do
    user = User.new(email: 'test1@example.com', password: 'test1234')
    order = Order.new(user: user)
    order_item = OrderItem.new(order: order, item_unit_price: 100, quantity: 2)
end
   it 'calculates order total' do
     expect(order.total_price).to eq(200)
   end
end