Set tax adjustment amount without persistance

To support the in-memory order updater, we want adjustments to be
modified without writing to the database immediately.

We added `autosave: true` in the association on line_items ensures that
the adjustment amount will be saved with the line_item, or by extension
the order when it is eventually persisted by the order updater.

The tests for the OrderTaxation have been updated to use `size` instead
of `count` to ensure an in-memory reported count/size.

Co-authored-by: Adam Mueller <[email protected]>
Co-authored-by: Andrew Stewart <[email protected]>
Co-authored-by: Jared Norman <[email protected]>
Co-authored-by: Noah Silvera <[email protected]>
Co-authored-by: benjamin wil <[email protected]>
Co-authored-by: Alistair Norman <[email protected]>

Author: 7 people

core/app/models/spree/line_item.rb

@@ -18,7 +18,7 @@ class LineItem < Spree::Base
 
     has_one :product, through: :variant
 
-    has_many :adjustments, as: :adjustable, inverse_of: :adjustable, dependent: :destroy
+    has_many :adjustments, as: :adjustable, inverse_of: :adjustable, dependent: :destroy, autosave: true
     has_many :inventory_units, inverse_of: :line_item
 
     before_validation :normalize_quantity

core/app/models/spree/order_taxation.rb

@@ -77,7 +77,8 @@ def update_adjustment(item, tax_item)
         label: tax_item.label,
         included: tax_item.included_in_price
       )
-      tax_adjustment.update!(amount: tax_item.amount)
+
+      tax_adjustment.amount = tax_item.amount
       tax_adjustment
     end
   end

core/spec/models/spree/order_taxation_spec.rb

@@ -68,7 +68,7 @@
 
     it "creates a new tax adjustment", aggregate_failures: true do
       apply
-      expect(line_item.adjustments.count).to eq 1
+      expect(line_item.adjustments.size).to eq 1
 
       tax_adjustment = line_item.adjustments.first
       expect(tax_adjustment.label).to eq "Tax!"
@@ -136,7 +136,7 @@
         expect {
           taxation.apply(new_taxes)
         }.to change {
-          line_item.adjustments.count
+          line_item.adjustments.size
         }.from(1).to(0)
       end
     end
@@ -174,7 +174,7 @@
       end
 
       it "creates a new tax adjustment", aggregate_failures: true do
-        expect(order.adjustments.count).to eq 1
+        expect(order.adjustments.size).to eq 1
 
         tax_adjustment = order.adjustments.first
         expect(tax_adjustment.label).to eq "Order Tax!"