Add persist flag to #recalculate

We want our new in-memory order updater to be able to persist or not
persist changes to the order record.

WORK IN PROGRESS

This is a first step in ensuring we don't need to write to the database
using the order updater. Clearly we have more work to do to ensure this
functions like the existing updater.

core/app/models/spree/in_memory_order_updater.rb

@@ -16,7 +16,7 @@ def initialize(order)
     # This method should never do anything to the Order that results in a save call on the
     # object with callbacks (otherwise you will end up in an infinite recursion as the
     # associations try to save and then in turn try to call +update!+ again.)
-    def recalculate
+    def recalculate(persist: true)
       order.transaction do
         update_item_count
         update_shipment_amounts
@@ -27,7 +27,8 @@ def recalculate
           update_shipment_state
         end
         Spree::Bus.publish :order_recalculated, order: order
-        persist_totals
+
+        persist_totals if persist
       end
     end
     alias_method :update, :recalculate

core/spec/models/spree/in_memory_order_updater_spec.rb

@@ -8,6 +8,52 @@ module Spree
     let(:order) { Spree::Order.create }
     let(:updater) { described_class.new(order) }
 
+    describe "#recalculate" do
+      subject { updater.recalculate(persist:) }
+
+      let(:new_store) { create(:store) }
+
+      context "when the persist flag is set to 'false'" do
+        let(:persist) { false }
+
+        it "does not persist changes to order" do
+          order.store = new_store
+
+          expect {
+            subject
+          }.not_to make_database_queries(manipulative: true)
+
+          expect(order.store).to eq new_store
+          expect(order.reload.store).not_to eq new_store
+        end
+
+        it "does not persist changes to the item count" do
+          order.line_items << build(:line_item)
+
+          expect {
+            subject
+          }.not_to make_database_queries(manipulative: true)
+
+          expect(order.item_count).to eq 1
+          expect(order.reload.item_count).to eq 0
+        end
+      end
+
+      context "when the persist flag is set to 'true'" do
+        let(:persist) { true }
+
+        it "persists any changes to order" do
+          order.store = new_store
+
+          expect {
+            subject
+          }.to make_database_queries(manipulative: true)
+
+          expect(order.reload.store).to eq new_store
+        end
+      end
+    end
+
     context "order totals" do
       before do
         2.times do