Autosave shipment adjustments to persist taxes on recalculate

A commit was made in #6315 (5979f25) in service of the in memory order updater #5872 that changed the behavior in the OrderTaxation class to set the adjustment value but not persist it. Instead, the persistence happens when the order is saved. If a shipment is changed, and an associated adjustment is changed, the shipment adjustment will be autosaved when the order is.

However, if a shipment is *not* changed, but the adjustment is, the adjustment will *not* be autosaved when the order is.

In #6315, we ensured that these changed associations cannot get left behind by setting `autosave: true`, which forces the model to check if it has any associations that need saving instead of telling it's relation "nope I haven't changed"

We can do the same thing here for the shipment to ensure changing  adjustments will make the shipment tell it's order "I have changed", even if none of it's direct properties have changed.

You can test this change by removing the `autosave: true` option the adjustments and running 'when the address has changed to a different state' specs. They fail with the error "expected `order.shipments.first.adjustments.first.amount` to have changed from 1 to 2, but did not change", demonstrating a scenario where the shipment adjustment changes do not get persisted.

Author: Noah-Silvera

core/app/models/spree/shipment.rb

@@ -9,7 +9,7 @@ class Shipment < Spree::Base
     belongs_to :order, class_name: 'Spree::Order', touch: true, inverse_of: :shipments, optional: true
     belongs_to :stock_location, class_name: 'Spree::StockLocation', optional: true
 
-    has_many :adjustments, as: :adjustable, inverse_of: :adjustable, dependent: :delete_all
+    has_many :adjustments, as: :adjustable, inverse_of: :adjustable, dependent: :delete_all, autosave: true
     has_many :inventory_units, dependent: :destroy, inverse_of: :shipment
     has_many :shipping_rates, -> { order(:cost) }, dependent: :destroy, inverse_of: :shipment
     has_many :shipping_methods, through: :shipping_rates

core/spec/models/spree/order_updater_spec.rb

@@ -72,14 +72,14 @@ module Spree
         let(:tax_category) { create(:tax_category) }
         let(:ship_address) { create(:address, state: new_york) }
         let(:new_york) { create(:state, state_code: "NY") }
-        let(:tax_zone) { create(:zone, states: [new_york]) }
+        let(:new_york_tax_zone) { create(:zone, states: [new_york]) }
 
-        let!(:tax_rate) do
+        let!(:new_york_tax_rate) do
           create(
             :tax_rate,
             name: "New York Sales Tax",
             tax_categories: [tax_category],
-            zone: tax_zone,
+            zone: new_york_tax_zone,
             included_in_price: false,
             amount: 0.1
           )
@@ -111,21 +111,67 @@ module Spree
         end
 
         context 'when the address has changed to a different state' do
-          let(:new_shipping_address) { create(:address) }
+          let(:oregon) { create(:state, state_code: "OR") }
+          let(:oregon_tax_zone) { create(:zone, states: [oregon]) }
+          let!(:oregon_tax_rate) do
+            create(
+              :tax_rate,
+              name: "Oregon Sales Tax",
+              tax_categories: [tax_category],
+              zone: oregon_tax_zone,
+              included_in_price: false,
+              amount: 0.2
+            )
+          end
+          let(:new_address) { create(:address, state: oregon) }
+          let(:shipping_method) { create(:shipping_method, tax_category:, zones: [oregon_tax_zone, new_york_tax_zone], cost: 10) }
+          let(:shipping_rate) do
+            create(:shipping_rate, cost: 10, shipping_method: shipping_method)
+          end
+          let(:shipment) { order.shipments[0] }
+
+          subject do
+            order.ship_address = new_address
+            order.bill_address = new_address
+
+            order.recalculate
+          end
 
           before do
-            order.ship_address = new_shipping_address
+            shipment.shipping_rates = [shipping_rate]
+            shipment.selected_shipping_rate_id = shipping_rate.id
+            order.recalculate
           end
 
-          it 'removes the old taxes' do
+          it 'updates the taxes to reflect the new state' do
             expect {
-              order.recalculate
+              subject
             }.to change {
-              order.all_adjustments.tax.count
-            }.from(1).to(0)
+              order.additional_tax_total
+            }.from(2).to(4)
+          end
 
-            expect(order.additional_tax_total).to eq 0
-            expect(order.adjustment_total).to eq 0
+          it 'updates the shipment taxes to reflect the new state' do
+            $started_spec = true
+            expect {
+              subject
+            }.to change {
+              order.shipments.first.additional_tax_total
+            }.from(1).to(2)
+            .and change {
+              order.shipments.first.adjustments.first.amount
+            }.from(1).to(2)
+          end
+
+          it 'updates the line item taxes to reflect the new state' do
+            expect {
+              subject
+            }.to change {
+              order.line_items.first.additional_tax_total
+            }.from(1).to(2)
+            .and change {
+              order.line_items.first.adjustments.first.amount
+            }.from(1).to(2)
           end
         end
 
@@ -179,7 +225,7 @@ module Spree
                 order_taxes: [
                   Spree::Tax::ItemTax.new(
                     label: "Delivery Fee",
-                    tax_rate:,
+                    tax_rate: new_york_tax_rate,
                     amount: 2.60,
                     included_in_price: false
                   )
@@ -188,7 +234,7 @@ module Spree
                   Spree::Tax::ItemTax.new(
                     item_id: line_item.id,
                     label: "Item Tax",
-                    tax_rate:,
+                    tax_rate: new_york_tax_rate,
                     amount: 1.40,
                     included_in_price: false
                   )