Fix invoice

#623

app/models/invoice.rb

@@ -160,6 +160,7 @@ class Invoice < ActiveRecord::Base
 
   def total
     calculate_total unless total?
+    read_attribute(:total)
   end
 
   private

test/models/invoice_test.rb

@@ -76,6 +76,10 @@ class InvoiceTest < ActiveSupport::TestCase
     end
   end
 
+  def test_returns_persisted_total
+    assert_equal BigDecimal('16.50'), @invoice.total
+  end
+
   def test_calculates_total
     line_item = InvoiceItem.new
     invoice = Invoice.new