Check if internal payment can be voided

Add extra security, we don't want to void a credit payment that is not
completed, otherwise we would be refunding credit that was not used.
A credit payment should not be in a non completed state, but you never
know.

app/models/spree/payment/processing.rb

@@ -146,6 +146,9 @@ module Spree
 
       def internal_void!
         return true if void?
+        # We should only void complete payment, otherwise we will be refunding credit that was
+        # not used in the first place.
+        return gateway_error(Spree.t(:internal_payment_not_voidable)) if state != "completed"
 
         options = { customer_id: order.customer_id, payment_id: id, order_number: order.number }
         response = payment_method.void(

config/locales/en.yml

@@ -4196,6 +4196,7 @@ en:
     items_cannot_be_shipped: "Items cannot be shipped"
     gateway_config_unavailable: "Gateway config unavailable"
     gateway_error: "Payment failed"
+    internal_payment_not_voidable: Payment not voidable
     more: "More"
     new_adjustment: "New adjustment"
     new_tax_category: "New Tax Category"

spec/models/spree/payment_spec.rb

@@ -944,6 +944,13 @@ RSpec.describe Spree::Payment do
     end
 
     describe "internal_void!" do
+      let(:payment) do
+        payment = create(:payment, :completed)
+        payment.order = order
+        payment.payment_method = payment_method
+        payment
+      end
+
       let(:order) { create(:order, customer:) }
       let(:customer) { create(:customer) }
       let(:payment_method) {
@@ -1018,6 +1025,17 @@ RSpec.describe Spree::Payment do
           payment.internal_void!
         end
       end
+
+      context "when payment not voidable" do
+        it "raises an error" do
+          payment.update(state: "pending")
+          expect(payment_method).not_to receive(:void)
+
+          expect {
+            payment.internal_void!
+          }.to raise_error(Spree::Core::GatewayError, "Payment not voidable")
+        end
+      end
     end
 
     describe "applying transaction fees" do