test: add test case for coupon without maximum use

(cherry picked from commit 3413bad51d)

erpnext/accounts/doctype/coupon_code/test_coupon_code.py

@@ -142,3 +142,39 @@ class TestCouponCode(unittest.TestCase):
 
 		so.submit()
 		self.assertEqual(frappe.db.get_value("Coupon Code", "SAVE30", "used"), 1)
+
+	def test_coupon_without_max_use(self):
+		from erpnext.accounts.doctype.pricing_rule.utils import (
+			update_coupon_code_count,
+			validate_coupon_code,
+		)
+
+		coupon = frappe.get_doc(
+			{
+				"doctype": "Coupon Code",
+				"coupon_name": "_Test Coupon Without Max Use",
+				"coupon_code": "TESTUNLIMITED",
+				"from_external_ecomm_platform": 1,  # avoids requirement for pricing rule
+				"valid_from": frappe.utils.nowdate(),
+				"maximum_use": 0,
+				"used": 0,
+			}
+		)
+		coupon.insert(ignore_permissions=True)
+
+		# Validate initial state
+		self.assertEqual(coupon.used, 0)
+		self.assertEqual(coupon.maximum_use, 0)
+
+		# Use coupon multiple times
+		for _ in range(5):
+			validate_coupon_code(coupon.name)
+			update_coupon_code_count(coupon.name, "used")
+			coupon.reload()
+
+		# Check that the coupon is still valid and usage count increased
+		self.assertEqual(coupon.used, 5)
+		validate_coupon_code(coupon.name)  # This should not raise an error
+
+		# Clean up
+		coupon.delete()