The shipping rates refresh process changed a little in spree 2.1 and the selection is and was random, it picks the first acceptable

In this case we need to specifically select one shipping method so that the test is valid

spec/services/order_syncer_spec.rb

@@ -15,6 +15,7 @@ describe OrderSyncer do
       before do
         # Create shipping rates for available shipping methods.
         order.shipments.each(&:refresh_rates)
+        order.select_shipping_method(shipping_method)
       end
 
       it "updates the shipping_method on the order and on shipments" do