Add test coverage to #create_tax_charge! with legacy taxes

spec/models/spree/order/tax_spec.rb

@@ -113,5 +113,60 @@ module Spree
         end
       end
     end
+
+    describe "#create_tax_charge!" do
+      context "handling legacy taxes" do
+        let(:order) { create(:order) }
+        let(:zone) { create(:zone_with_member) }
+        let(:tax_rate20) {
+          create(:tax_rate, amount: 0.20, included_in_price: false, zone: zone)
+        }
+        let(:tax_rate30) {
+          create(:tax_rate, amount: 0.30, included_in_price: false, zone: zone)
+        }
+        let!(:variant) {
+          create(:variant, tax_category: tax_rate20.tax_category, price: 10)
+        }
+        let!(:line_item) {
+          create(:line_item, variant: variant, order: order, quantity: 2)
+        }
+        let!(:shipping_method) {
+          create(:shipping_method, tax_category: tax_rate30.tax_category)
+        }
+        let!(:shipment) {
+          create(:shipment_with, :shipping_method, order: order, cost: 50,
+                                                   shipping_method: shipping_method)
+        }
+
+        before do
+          shipment.update_columns(cost: 20.0)
+          order.reload
+
+          allow(order).to receive(:completed_at) { Time.zone.now }
+          allow(order).to receive(:tax_zone) { zone }
+        end
+
+        context "when the order has legacy taxes" do
+          let!(:legacy_tax_adjustment) {
+            create(:adjustment, order: order, adjustable: order, included: false,
+                                label: "legacy", originator_type: "Spree::TaxRate")
+          }
+
+          it "removes any legacy tax adjustments on order" do
+            order.create_tax_charge!
+
+            expect(order.reload.adjustments).to_not include legacy_tax_adjustment
+          end
+
+          it "re-applies taxes on individual items" do
+            order.create_tax_charge!
+
+            expect(order.all_adjustments.tax.count).to eq 2
+            expect(line_item.adjustments.tax.first.amount).to eq 4
+            expect(shipment.adjustments.tax.first.amount).to eq 6
+          end
+        end
+      end
+    end
   end
 end