Moved order.shipping_method to the OrderShippingMethod concern

app/models/concerns/order_shipping_method.rb

@@ -0,0 +1,21 @@
+require 'active_support/concern'
+
+# This module is an adapter for OFN to work with Spree 2 code.
+#
+# Although Spree 2 supports multiple shipments per order, in OFN we have only one shipment per order.
+# A shipment is associated to a shipping_method through a selected shipping_rate.
+# See https://github.com/openfoodfoundation/openfoodnetwork/wiki/Spree-Upgrade:-Migration-to-multiple-shipments
+# for details.
+#
+# Methods in this module may become deprecated.
+module OrderShippingMethod
+  extend ActiveSupport::Concern
+
+  # Returns the shipping method of the first and only shipment in the order
+  #
+  # @return [ShippingMethod]
+  def shipping_method
+    return if shipments.empty?
+    shipments.first.shipping_method
+  end
+end

app/models/spree/order_decorator.rb

@@ -2,12 +2,15 @@ require 'open_food_network/enterprise_fee_calculator'
 require 'open_food_network/distribution_change_validator'
 require 'open_food_network/feature_toggle'
 require 'open_food_network/tag_rule_applicator'
+require 'concerns/order_shipping_method'
 
 ActiveSupport::Notifications.subscribe('spree.order.contents_changed') do |name, start, finish, id, payload|
   payload[:order].reload.update_distribution_charge!
 end
 
 Spree::Order.class_eval do
+  include OrderShippingMethod
+
   belongs_to :order_cycle
   belongs_to :distributor, class_name: 'Enterprise'
   belongs_to :customer
@@ -333,13 +336,6 @@ Spree::Order.class_eval do
     payments.select {|p| p.state == "checkout"} # Original definition
   end
 
-  # Although Spree 2 supports multi shipments per order, in OFN we keep the rule one shipment per order
-  #   Thus, this method returns the shipping method of the first and only shipment in the order
-  def shipping_method
-    return if shipments.empty?
-    shipments.first.shipping_method
-  end
-
   private
 
   def address_from_distributor

spec/models/concerns/order_shipping_method_spec.rb

@@ -0,0 +1,22 @@
+require 'spec_helper'
+
+describe OrderShippingMethod do
+  let(:order) { create(:order) }
+
+  describe '#shipping_method' do
+    context 'when order has no shipments' do
+      it 'returns nil' do
+        expect(order.shipping_method).to be_nil
+      end
+    end
+
+    context 'when order has single shipment' do
+      it 'returns the shipments shipping_method' do
+        shipment = create(:shipment_with_flat_rate)
+        order.shipments = [shipment]
+
+        expect(order.shipping_method).to eq shipment.shipping_method
+      end
+    end
+  end
+end