Enhance InvoiceItem

#329

app/models/invoice_item.rb

@@ -2,7 +2,18 @@ class InvoiceItem < ActiveRecord::Base
   include Versions
   belongs_to :invoice
 
+  delegate :vat_rate, to: :invoice
+
   def item_sum_without_vat
     (price * quantity).round(2)
   end
-end
+  alias_method :subtotal, :item_sum_without_vat
+
+  def vat_amount
+    subtotal * (vat_rate / 100)
+  end
+
+  def total
+    subtotal + vat_amount
+  end
+end

test/models/invoice_item_test.rb

@@ -1,8 +1,30 @@
 require 'test_helper'
 
 class InvoiceItemTest < ActiveSupport::TestCase
-  def test_calculates_sum_without_vat
+  def test_calculates_subtotal
     invoice_item = InvoiceItem.new(price: 5, quantity: 2)
     assert_equal 10, invoice_item.item_sum_without_vat
+    assert_equal 10, invoice_item.subtotal
   end
-end
+
+  def test_returns_vat_rate
+    vat_rate = 20
+    invoice = Invoice.new(vat_rate: vat_rate)
+
+    invoice_item = InvoiceItem.new(invoice: invoice)
+
+    assert_equal vat_rate, invoice_item.vat_rate
+  end
+
+  def test_calculates_vat_amount
+    invoice = Invoice.new(vat_rate: 20)
+    invoice_item = InvoiceItem.new(price: 5, quantity: 2, invoice: invoice)
+    assert_equal 2, invoice_item.vat_amount
+  end
+
+  def test_calculates_total
+    invoice = Invoice.new(vat_rate: 20)
+    invoice_item = InvoiceItem.new(price: 5, quantity: 2, invoice: invoice)
+    assert_equal 12, invoice_item.total
+  end
+end