Update specs that stub associations inaccurately

These specs fail if the code is using #sum on stubbed objects that don't respond to it nicely.

engines/order_management/spec/services/order_management/order/updater_spec.rb

@@ -11,14 +11,12 @@ module OrderManagement
       before { allow(order).to receive(:backordered?) { false } }
 
       it "updates totals" do
-        payments = [double(amount: 5), double(amount: 5)]
-        allow(order).to receive_message_chain(:payments, :completed).and_return(payments)
+        allow(order).to receive_message_chain(:payments, :completed, :sum).and_return(10)
 
         line_items = [double(amount: 10), double(amount: 20)]
         allow(order).to receive_messages line_items: line_items
 
-        adjustments = [double(amount: 10), double(amount: -20)]
-        allow(order).to receive_message_chain(:adjustments, :eligible).and_return(adjustments)
+        allow(order).to receive_message_chain(:adjustments, :eligible, :sum).and_return(-10)
 
         updater.update_totals
         expect(order.payment_total).to eq 10

spec/models/spree/order/adjustments_spec.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require 'spec_helper'
+
 describe Spree::Order do
   let(:order) { Spree::Order.new }
 
@@ -21,19 +22,20 @@ describe Spree::Order do
   end
 
   context "totaling adjustments" do
-    let(:adjustment1) { build(:adjustment, amount: 5) }
-    let(:adjustment2) { build(:adjustment, amount: 10) }
+    let!(:adjustment1) { create(:adjustment, amount: 5) }
+    let!(:adjustment2) { create(:adjustment, amount: 10) }
+    let(:adjustments) { Spree::Adjustment.where(id: [adjustment1, adjustment2]) }
 
     context "#ship_total" do
       it "should return the correct amount" do
-        allow(order).to receive_message_chain :adjustments, shipping: [adjustment1, adjustment2]
+        allow(order).to receive_message_chain :adjustments, shipping: adjustments
         expect(order.ship_total).to eq 15
       end
     end
 
     context "#tax_total" do
       it "should return the correct amount" do
-        allow(order).to receive_message_chain :adjustments, tax: [adjustment1, adjustment2]
+        allow(order).to receive_message_chain :adjustments, tax: adjustments
         expect(order.tax_total).to eq 15
       end
     end