Handle unique voucher code exception

Rails validation doesn't handle unique validation for soft deleted
object. So we rescue the exception raise by the database and display
a nice error message. We don't want an enterprise to be able to reuse
a code in case the voucher get reactivated.

app/controllers/admin/vouchers_controller.rb

@@ -22,6 +22,11 @@ module Admin
     rescue ActiveRecord::SubclassNotFound
       @voucher.errors.add(:type)
       render_error
+    rescue ActiveRecord::RecordNotUnique
+      # Rails unique validation doesn't work with soft deleted object, so we rescue the database
+      # exception  to display a nice message to the user
+      @voucher.errors.add(:code, :taken)
+      render_error
     end
 
     private

spec/requests/admin/vouchers_spec.rb

@@ -81,6 +81,20 @@ describe "/admin/enterprises/:enterprise_id/vouchers", type: :request do
       end
     end
 
+    context "with a code used by a deactivated voucher" do
+      before do
+        voucher = create(:voucher, code:, enterprise:)
+        voucher.destroy
+      end
+
+      it "render the new page with a code taken error" do
+        create_voucher
+
+        expect(response).to render_template("admin/vouchers/new")
+        expect(flash[:error]).to eq("Code has already been taken")
+      end
+    end
+
     it "redirects to admin enterprise setting page, voucher panel" do
       create_voucher