Update RSpec for Order model

app/controllers/orders_controller.rb

@@ -43,8 +43,9 @@ class OrdersController < ApplicationController
 
   def save_order_items(order)
     @cart.product_items.values.each do |attrs|
-      order.product_items.create(product: attrs[:product],
+      product_item = order.product_items.create(product: attrs[:product],
                                                 quantity: attrs[:quantity])
+      product_item.update_product_quantity
     end
   end
 

app/models/product_item.rb

 class ProductItem < ApplicationRecord
   belongs_to :product, optional: true
   belongs_to :order, optional: true
-  after_create :update_product_quantity
 
   validates :quantity, numericality: { only_integer: true,
                                        greater_than: 0 }

spec/models/order_spec.rb

@@ -15,4 +15,16 @@ RSpec.describe Order, type: :model do
     it { is_expected.to belong_to(:user) }
     it { is_expected.to have_many(:product_items) }
   end
+
+  context 'custom methods' do
+    it 'has valid total_price' do
+      user = create(:user)
+      order = create(:order, user: user)
+      product = create(:product, quantity: 3, price: 10)
+      ProductItem.create(quantity: 2,
+                         product_id: product.id,
+                         order: order)
+      expect(order.total_price).to eq 20
+    end
+  end
 end