Display total value with tax on the invoice

- added acceptance test
- implemented as methods on ActiveRecord
- Vat Rate was already stored and displayed

Idea for the future: store product/vat matching in the read model here.
Then we can remove the DetermineVatRate process manager which feels artificial.

Author: andrzejkrzywda

rails_application/app/read_models/invoices/configuration.rb

@@ -2,11 +2,19 @@ module Invoices
   class Invoice < ApplicationRecord
     self.table_name = "invoices"
     has_many :invoice_items
+
+    def total_value_with_tax
+      invoice_items.sum(&:value_with_tax)
+    end
   end
 
   class InvoiceItem < ApplicationRecord
     self.table_name = "invoice_items"
     belongs_to :invoice
+
+    def value_with_tax
+      value + (value * vat_rate / 100)
+    end
   end
 
   class Order < ApplicationRecord

rails_application/app/views/invoices/show.html.erb

@@ -34,7 +34,8 @@
     <th class="text-left py-2">VAT rate</th>
     <th class="text-left py-2">Quantity</th>
     <th class="text-left py-2">Unit Price</th>
-    <th class="text-right py-2">Value</th>
+    <th class="text-right py-2">Value (net)</th>
+    <th class="text-right py-2">Value + VAT</th>
   </tr>
   </thead>
 
@@ -46,13 +47,15 @@
       <td class="py-2"><%= item.quantity %></td>
       <td class="py-2"><%= number_to_currency(item.unit_price) %></td>
       <td class="py-2 text-right"><%= number_to_currency(item.value) %></td>
+      <td class="py-2 text-right"><%= number_to_currency(item.value_with_tax) %></td>
     </tr>
   <% end %>
   </tbody>
   <tfoot>
   <tr class="border-t">
     <td class="py-2" colspan="4">Total</td>
-    <td class="py-2 text-right font-bold"><%= number_to_currency(@invoice.total_value) %></td>
+    <td class="py-2 text-right"><%= number_to_currency(@invoice.total_value) %></td>
+    <td class="py-2 text-right font-bold"><%= number_to_currency(@invoice.total_value_with_tax) %></td>
   </tr>
   </tfoot>
 </table>

rails_application/test/invoices/invoices_test.rb

@@ -19,7 +19,6 @@ def test_create_draft_order_when_not_exists
     end
 
     def test_product_name_change_affects_existing_invoices
-      product_id = SecureRandom.uuid
       initial_product_name = "Initial Name"
       updated_product_name = "Updated Name"
 
@@ -42,6 +41,18 @@ def test_product_name_change_affects_existing_invoices
       assert_invoice_product_name(new_order_id, updated_product_name)
     end
 
+    def test_invoice_value_with_taxes
+      add_available_vat_rate(20)
+      product_id = register_product("Test Product", 100, 20)
+      customer_id = register_customer("Test Customer")
+
+      order_id = SecureRandom.uuid
+      add_product_to_basket(order_id, product_id)
+      submit_order(customer_id, order_id)
+
+      assert_invoice_value_with_taxes(order_id, 120)
+    end
+
     private
 
     def update_product_name(product_id, new_name)
@@ -58,5 +69,11 @@ def assert_invoice_product_name(order_id, expected_name)
       assert_response :success
       assert_select ".py-2", text: expected_name
     end
+
+    def assert_invoice_value_with_taxes(order_id, expected_value)
+      get "/invoices/#{order_id}"
+      assert_response :success
+      assert_select "td.font-bold", text: "$#{expected_value}.00"
+    end
   end
 end