Add a scenario to make sure voucher adjustment a recalculated

This is specificly for voucher with a tax component, but it will
also become relevant for percentage based voucher.

spec/system/consumer/split_checkout_tax_incl_spec.rb

@@ -49,7 +49,7 @@ describe "As a consumer, I want to see adjustment breakdown" do
   let!(:order_within_zone) {
     create(:order, order_cycle: order_cycle, distributor: distributor, user: user_within_zone,
                    bill_address: address_within_zone, ship_address: address_within_zone,
-                   state: "cart", line_items: [create(:line_item, variant: variant_with_tax)])
+                   state: "cart", line_items: [create(:line_item, variant: variant_with_tax, quantity: 1)])
   }
   let!(:order_outside_zone) {
     create(:order, order_cycle: order_cycle, distributor: distributor, user: user_outside_zone,
@@ -139,11 +139,65 @@ describe "As a consumer, I want to see adjustment breakdown" do
           end
 
           # DB check
-          order_within_zone.reload
-          voucher_adjustment = order_within_zone.voucher_adjustments.first
+          assert_db_voucher_adjustment(-10.00, -1.15)
+        end
 
-          expect(voucher_adjustment.amount.to_f).to eq(-10)
-          expect(voucher_adjustment.included_tax.to_f).to eq(-1.15)
+        describe "moving between summary to summary via edit cart" do
+          let!(:voucher) do
+            create(:voucher, code: 'good_code', enterprise: distributor, amount: 15)
+          end
+
+          it "recalculate the tax component properly" do
+            visit checkout_step_path(:details)
+            proceed_to_payment
+
+            # add Voucher
+            fill_in "Enter voucher code", with: voucher.code
+            click_button("Apply")
+
+            proceed_to_summary
+
+            assert_db_voucher_adjustment(-10.00, -1.15)
+
+            # Click on edit link
+            within "div", text: /Order details/ do
+              # It's a bit brittle, but the scoping doesn't seem to work
+              all(".summary-edit").last.click
+            end
+
+            # Update quantity
+            within ".cart-item-quantity" do
+              input = find(".line_item_quantity")
+              input.send_keys :up
+            end
+
+            click_button("Update")
+
+            # Check adjustment has been recalculated
+            assert_db_voucher_adjustment(-15.00, -1.73)
+
+            within "#cart-container" do
+              click_link("Checkout")
+            end
+
+            # Go back to payment step
+            proceed_to_payment
+
+            # Check voucher is still there
+            expect(page).to have_content("$15.00 Voucher")
+
+            # Go to summary
+            proceed_to_summary
+
+            # Check voucher value
+            within ".summary-right" do
+              expect(page).to have_content "good_code"
+              expect(page).to have_content "-15"
+            end
+
+            # Check adjustment has been recalculated, we are not expecting any changes here
+            assert_db_voucher_adjustment(-15.00, -1.73)
+          end
         end
       end
     end
@@ -190,4 +244,11 @@ describe "As a consumer, I want to see adjustment breakdown" do
     expect(order_outside_zone.included_tax_total).to eq(0.0)
     expect(order_outside_zone.additional_tax_total).to eq(0.0)
   end
+
+  def assert_db_voucher_adjustment(amount, tax_amount)
+    adjustment = order_within_zone.voucher_adjustments.first
+    #adjustment.reload
+    expect(adjustment.amount.to_f).to eq(amount)
+    expect(adjustment.included_tax.to_f).to eq(tax_amount)
+  end
 end