Spec for customer return referencing existing items

This change adds a pending test which demonstrates an issue with the
`create` action when attempting to pass a reference to existing return
items from a previously created return authorization. Rails does not
allow us to update the association on the return items to the customer
return while creating the return.

Co-authored-by: Mike Conlin <mike@super.gd>

api/spec/requests/spree/api/customer_returns_controller_spec.rb

@@ -133,6 +133,43 @@ module Spree
         end
       end
 
+      context "when referencing existing return items" do
+        subject do
+          post(
+            spree.api_order_customer_returns_path(order),
+            params: {
+              order_id: order.number,
+              customer_return: customer_return_params
+            }
+          )
+        end
+
+        let(:stock_location) { create(:stock_location) }
+        let(:inventory_unit) { create(:inventory_unit, state: "shipped") }
+        let(:return_item) do
+          create(:return_item, inventory_unit: inventory_unit)
+        end
+
+        let(:customer_return_params) do
+          {
+            stock_location_id: stock_location.id,
+            return_items_attributes: [
+              return_item.attributes.merge(reception_status_event: "receive")
+            ]
+          }
+        end
+
+        it "can create a new customer return" do
+          pending("fix for referrencing existing return items")
+          subject
+
+          expect(response).to have_http_status(:success)
+          expect(json_response).to have_attributes(attributes)
+
+          customer_return = Spree::CustomerReturn.last
+
+          expect(customer_return.return_items.first.reception_status).to eql "received"
+        end
       end
     end
   end