Pull out the item total updater

We want to start breaking out some of the complex logic of the in memory
updater into smaller more focused classes.

Co-Authored-By: Adam Mueller <[email protected]>
Co-Authored-By: Benjamin Willems <[email protected]>
Co-Authored-By: Andrew Stewart <[email protected]>
Co-Authored-By: Harmony Bouvier <[email protected]>
Co-Authored-By: Jared Norman <[email protected]>
Co-Authored-By: Kendra Riga <[email protected]>
Co-Authored-By: Sofia Besenski <[email protected]>
Co-Authored-By: Chris Todorov <[email protected]>
Co-Authored-By: Tom Van Manen <[email protected]>
Co-Authored-By: Noah Silvera <[email protected]>

core/app/models/spree/in_memory_order_updater.rb

@@ -180,11 +180,7 @@ def update_cancellations
 
     def update_item_totals(persist:)
       [*line_items, *shipments].each do |item|
-        # The cancellation_total isn't persisted anywhere but is included in
-        # the adjustment_total
-        item.adjustment_total = item.adjustments.
-          reject(&:included?).
-          sum(&:amount)
+        Spree::ItemTotalUpdater.recalculate(item)
 
         if persist && item.changed?
           item.update_columns(

core/app/models/spree/item_total_updater.rb

@@ -0,0 +1,9 @@
+class Spree::ItemTotalUpdater
+  class << self
+    def recalculate(item)
+      item.adjustment_total = item.adjustments
+        .reject(&:included?)
+        .sum(&:amount)
+    end
+  end
+end

core/spec/models/spree/item_total_updater_spec.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe Spree::ItemTotalUpdater do
+  describe ".recalculate" do
+    subject { described_class.recalculate(item) }
+
+    let(:item) { create :line_item, adjustments: [adjustment] }
+    let(:adjustment) { create :adjustment, amount: 1}
+
+    it "sets the adjustment total on the item" do
+      expect { subject }
+        .to change { item.adjustment_total }
+        .from(0).to(1)
+    end
+  end
+end