allow to synchronize all articles of a shared supplier

spec/factories/article.rb

@@ -9,7 +9,7 @@ FactoryGirl.define do
     tax { [6, 21].sample }
     deposit { rand(10) < 8 ? 0 : [0.0, 0.80, 1.20, 12.00].sample }
     unit_quantity { rand(5) < 3 ? 1 : rand(1..20) }
-    #supplier_id
+    supplier { create :supplier }
     article_category { create :article_category }
   end
 

spec/models/article_spec.rb

@@ -108,7 +108,7 @@ describe Article do
 
     it 'does not synchronise when it has no order number' do
       article.update_attributes :order_number => nil
-      expect(supplier.sync_all).to eq [[], []]
+      expect(supplier.sync_all).to eq [[], [], []]
     end
   end
 end