Simple implementation of subscription trial period

argocd_sale/tests/test_free_period.py

@@ -41,7 +41,25 @@ def test_next_payment_date(self):
         sub.generate_invoice()
         sub._invoice_paid_hook()
         self.assertEqual(
-            sub.invoice_ids[0].amount_untaxed,
+            sub.invoice_ids[0].amount_untaxed,  # It's order newest to oldest
             30.0,
             "Next invoice should be the normal price",
         )
+
+        sub2 = self.env["sale.subscription"].create(
+            {
+                "template_id": sub_tmpl.id,
+                "sale_subscription_line_ids": [
+                    Command.create({"product_id": sub_product.id})
+                ],
+                "partner_id": partner_id.id,
+                "pricelist_id": partner_id.property_product_pricelist.id,
+            }
+        )
+        sub2.generate_invoice()
+        sub2._invoice_paid_hook()
+        self.assertEqual(
+            sub2.invoice_ids.amount_untaxed,
+            30.0,
+            "Invoice of new second subscription must be the normal price",
+        )