WIP: Improving the dry run functionality before implementing persist

How dry run behaves is not consistent, and we think we can make not persisting easier if we first update the dry run functionality.

Author: Noah-Silvera

promotions/app/models/solidus_promotions/order_adjuster/discount_order.rb

@@ -17,6 +17,7 @@ def call
         SolidusPromotions::Promotion.ordered_lanes.each_key do |lane|
           lane_promotions = promotions.select { |promotion| promotion.lane == lane }
           lane_benefits = eligible_benefits_for_promotable(lane_promotions.flat_map(&:benefits), order)
+          # TODO: - (Noah & Sofia) think we should actually build/mark_for_destruction line items make/removed by CreateDiscountedItem on a dry run, and that's an improvement that would make implementing the persist flag easier also
           perform_order_benefits(lane_benefits, lane) unless dry_run
           line_item_discounts = adjust_line_items(lane_benefits)
           shipment_discounts = adjust_shipments(lane_benefits)

promotions/spec/models/solidus_promotions/order_adjuster_spec.rb

@@ -3,8 +3,9 @@
 require "rails_helper"
 
 RSpec.describe SolidusPromotions::OrderAdjuster, type: :model do
-  subject(:order_adjuster) { described_class.new(order) }
+  subject(:order_adjuster) { described_class.new(order, dry_run_promotion: dry_run_promotion) }
 
+  let(:dry_run_promotion) { nil }
   let(:line_item) { create(:line_item) }
   let(:order) { line_item.order }
   let(:promotion) { create(:solidus_promotion, apply_automatically: true) }
@@ -31,6 +32,26 @@
       expect(order.line_items.last.adjustments.promotion.first&.amount).to eq(-10)
     end
 
+    context 'when on a dry run' do
+      let(:dry_run_promotion) { create(:solidus_promotion, :with_adjustable_benefit, promotion_benefit_class: SolidusPromotions::Benefits::CreateDiscountedItem) }
+
+      subject do
+        benefit
+        order_adjuster.call
+      end
+
+      it 'builds the line item but does not save it' do
+        expect {
+          subject
+        }.to change { order.line_items.length }.by(1)
+
+        pending "currently on a dry run this just doesn't happen"
+        expect(order.line_items.last.variant).to eq(variant)
+        expect(order.line_items.last.adjustments.promotion.first&.amount).to eq(-10)
+
+        expect(order.reload.line_items.length).to eq(1)
+      end
+    end
   end
 
   context "adjusting line items" do