Use Spree::ItemAdjustments in Shipment callbacks for updating adjustments

app/models/spree/shipment.rb

@@ -15,7 +15,7 @@ module Spree
     has_many :adjustments, as: :adjustable, dependent: :destroy
 
     before_create :generate_shipment_number
-    after_save :ensure_correct_adjustment, :update_order
+    after_save :ensure_correct_adjustment, :update_adjustments
 
     attr_accessor :special_instructions
     alias_attribute :amount, :cost
@@ -344,8 +344,14 @@ module Spree
       end
     end
 
-    def update_order
-      order.reload.update!
+    def update_adjustments
+      return unless cost_changed? && state != 'shipped'
+
+      recalculate_adjustments
+    end
+
+    def recalculate_adjustments
+      Spree::ItemAdjustments.new(self).update
     end
   end
 end

spec/models/spree/shipment_spec.rb

@@ -423,13 +423,6 @@ describe Spree::Shipment do
     end
   end
 
-  context "update_order" do
-    it "should update order" do
-      expect(order).to receive_message_chain(:reload, :update!)
-      shipment.__send__(:update_order)
-    end
-  end
-
   describe "#update_amounts" do
     it "persists the shipping cost from the shipping fee adjustment" do
       allow(shipment).to receive(:fee_adjustment) { double(:adjustment, amount: 10) }
@@ -442,7 +435,7 @@ describe Spree::Shipment do
   context "after_save" do
     it "should run correct callbacks" do
       expect(shipment).to receive(:ensure_correct_adjustment)
-      expect(shipment).to receive(:update_order)
+      expect(shipment).to receive(:update_adjustments)
       shipment.run_callbacks(:save)
     end
   end