Extract property merging to lib class

app/models/spree/product_decorator.rb

@@ -1,4 +1,5 @@
 require 'open_food_network/permalink_generator'
+require 'open_food_network/property_merge'
 
 Spree::Product.class_eval do
   include PermalinkGenerator
@@ -128,11 +129,7 @@ Spree::Product.class_eval do
     ps = product_properties.all
 
     if inherits_properties
-      supplier.producer_properties.each do |producer_property|
-        unless ps.find { |product_property| product_property.property.presentation == producer_property.property.presentation }
-          ps << producer_property
-        end
-      end
+      ps = OpenFoodNetwork::PropertyMerge.merge(ps, supplier.producer_properties)
     end
 
     ps.

lib/open_food_network/property_merge.rb

@@ -0,0 +1,18 @@
+module OpenFoodNetwork
+  class PropertyMerge
+    def self.merge(primary, secondary)
+      primary + secondary.reject do |secondary_p|
+        primary.any? do |primary_p|
+          property_of(primary_p).presentation == property_of(secondary_p).presentation
+        end
+      end
+    end
+
+
+    private
+
+    def self.property_of(p)
+      p.respond_to?(:property) ? p.property : p
+    end
+  end
+end

spec/factories.rb

@@ -259,6 +259,12 @@ FactoryGirl.define do
     end
   end
 
+  factory :producer_property, class: ProducerProperty do
+    value 'abc123'
+    producer { create(:supplier_enterprise) }
+    property
+  end
+
   factory :customer, :class => Customer do
     email { Faker::Internet.email }
     enterprise

spec/lib/open_food_network/property_merge_spec.rb

@@ -0,0 +1,25 @@
+require 'spec_helper'
+
+module OpenFoodNetwork
+  describe PropertyMerge do
+    let(:p1a) { create(:property, presentation: 'One') }
+    let(:p1b) { create(:property, presentation: 'One') }
+    let(:p2)  { create(:property, presentation: 'Two') }
+
+    describe "merging Spree::Properties" do
+      it "merges properties" do
+        expect(PropertyMerge.merge([p1a], [p1b, p2])).to eq [p1a, p2]
+      end
+    end
+
+    describe "merging ProducerProperties and Spree::ProductProperties" do
+      let(:pp1a) { create(:product_property,  property: p1a) }
+      let(:pp1b) { create(:producer_property, property: p1b) }
+      let(:pp2)  { create(:producer_property, property: p2) }
+
+      it "merges properties" do
+        expect(PropertyMerge.merge([pp1a], [pp1b, pp2])).to eq [pp1a, pp2]
+      end
+    end
+  end
+end

spec/models/spree/product_spec.rb

@@ -420,7 +420,7 @@ module Spree
         end
       end
 
-      context "when product has an inherit_properties value set to true" do
+      context "when product has an inherit_properties value set to false" do
         let(:supplier) { create(:supplier_enterprise) }
         let(:product) { create(:simple_product, supplier: supplier, inherits_properties: false) }