allow non-shared articles to be part of a shared supplier using a blank order number

spec/models/article_spec.rb

@@ -105,5 +105,10 @@ describe Article do
       expect(article.unit_quantity).to eq 5
       expect(article.price).to be_within(1e-3).of(shared_article.price/5)
     end
+
+    it 'does not synchronise when it has no order number' do
+      article.update_attributes :order_number => nil
+      expect(supplier.sync_all).to eq [[], []]
+    end
   end
 end