Extract order total tax calculations to model

app/models/spree/order_decorator.rb

@@ -206,6 +206,9 @@ Spree::Order.class_eval do
     adjustments(:reload).enterprise_fee.sum(&:included_tax)
   end
 
+  def total_tax
+    (adjustments + price_adjustments).sum &:included_tax
+  end
 
   # Overrride of Spree method, that allows us to send separate confirmation emails to user and shop owners
   def deliver_order_confirmation_email

lib/open_food_network/sales_tax_report.rb

@@ -18,7 +18,7 @@ module OpenFoodNetwork
         shipping_cost = shipping_cost_for order
         shipping_tax = order.shipping_tax
         enterprise_fee_tax = order.enterprise_fee_tax
-        total_tax = (order.adjustments + order.price_adjustments).sum(&:included_tax)
+        total_tax = order.total_tax
 
         [order.number, order.created_at, totals[:items], totals[:items_total],
          totals[:taxable_total], totals[:sales_tax], shipping_cost, shipping_tax, enterprise_fee_tax, total_tax,

spec/models/spree/order_spec.rb

@@ -219,6 +219,24 @@ describe Spree::Order do
     end
   end
 
+  describe "getting the total tax" do
+    let(:order)           { create(:order, shipping_method: shipping_method) }
+    let(:shipping_method) { create(:shipping_method, calculator: Spree::Calculator::FlatRate.new(preferred_amount: 50.0)) }
+    let(:enterprise_fee)  { create(:enterprise_fee) }
+    let!(:adjustment)     { create(:adjustment, adjustable: order, originator: enterprise_fee, label: "EF", amount: 123, included_tax: 2) }
+
+    before do
+      Spree::Config.shipment_inc_vat = true
+      Spree::Config.shipping_tax_rate = 0.25
+      order.create_shipment!
+      order.reload
+    end
+
+    it "returns a sum of all tax on the order" do
+      order.total_tax.should == 12
+    end
+  end
+
   describe "setting the distributor" do
     it "sets the distributor when no order cycle is set" do
       d = create(:distributor_enterprise)