Sales Tax Totals by order, fix tax amount when voucher applied

Apply the tax discount to the tax collumn when a voucher is added
to the order, and update total excluding tax accordingly.

app/models/spree/adjustment.rb

@@ -70,6 +70,7 @@ module Spree
     scope :credit, -> { where('amount < 0') }
     scope :return_authorization, -> { where(originator_type: "Spree::ReturnAuthorization") }
     scope :voucher, -> { where(originator_type: "Voucher") }
+    scope :voucher_tax, -> { where(originator_type: "Voucher").where("label LIKE 'Tax%'") }
     scope :non_voucher, -> { where.not(originator_type: "Voucher") }
     scope :inclusive, -> { where(included: true) }
     scope :additional, -> { where(included: false) }

lib/reporting/reports/sales_tax/sales_tax_totals_by_order.rb

@@ -92,8 +92,8 @@ module Reporting
               summary_row: proc do |_key, items, _rows|
                 order = items.first.second
                 {
-                  total_excl_tax: order.total - order.total_tax,
-                  tax: order.total_tax,
+                  total_excl_tax: order.total - (order.total_tax + voucher_tax_adjustment(order)),
+                  tax: order.total_tax + voucher_tax_adjustment(order),
                   total_incl_tax: order.total,
                   first_name: order.customer&.first_name,
                   last_name: order.customer&.last_name,
@@ -130,20 +130,36 @@ module Reporting
         end
 
         def total_excl_tax(query_result_row)
-          order(query_result_row).total - order(query_result_row).total_tax
+          order = order(query_result_row)
+          total_excl_tax = order.total - order.total_tax
+
+          # Tax adjusment is a negative value, so we need to substract to add it to the total
+          total_excl_tax - voucher_tax_adjustment(order)
         end
 
         def tax_rate_total(query_result_row)
+          total_tax = non_adjusted_tax_rate_total(query_result_row)
+
+          # Tax adjustment is already a negative value
+          order = order(query_result_row)
+          total_tax + voucher_tax_adjustment(order)
+        end
+
+        def total_incl_tax(query_result_row)
+          order(query_result_row).total -
+            order(query_result_row).total_tax +
+            non_adjusted_tax_rate_total(query_result_row)
+        end
+
+        def non_adjusted_tax_rate_total(query_result_row)
           order(query_result_row).all_adjustments
             .tax
             .where(originator_id: tax_rate_id(query_result_row))
             .pick('sum(amount)') || 0
         end
 
-        def total_incl_tax(query_result_row)
-          order(query_result_row).total -
-            order(query_result_row).total_tax +
-            tax_rate_total(query_result_row)
+        def voucher_tax_adjustment(order)
+          order.all_adjustments.voucher_tax.first&.amount || 0
         end
 
         def first_name(query_result_row)

spec/system/admin/reports/sales_tax/sales_tax_totals_by_order_spec.rb

@@ -174,7 +174,7 @@ describe "Sales Tax Totals By order" do
         OrderWorkflow.new(order).complete!
       end
 
-      pending "generates the report with the correct tax amount" do
+      it "generates the report with the correct tax amount" do
         visit_sales_tax_totals_by_order
 
         expect(page).to have_button("Go")