Compute itemwise shipping cost for a line item

app/models/spree/line_item_decorator.rb

@@ -0,0 +1,5 @@
+Spree::LineItem.class_eval do
+  def itemwise_shipping_cost
+    self.product.shipping_cost_for_distributor(self.order.distributor)
+  end
+end

spec/models/line_item_spec.rb

@@ -0,0 +1,18 @@
+require 'spec_helper'
+
+module Spree
+  describe LineItem do
+    it "computes shipping cost for its product" do
+      distributor = double(:distributor)
+      order = double(:order, :distributor => distributor)
+
+      product = double(:product)
+      product.should_receive(:shipping_cost_for_distributor).with(distributor).and_return(10)
+
+      subject.stub(:order).and_return(order)
+      subject.stub(:product).and_return(product)
+
+      subject.itemwise_shipping_cost.should == 10
+    end
+  end
+end