fix: reject negative tax rate in Item Tax Template

erpnext/accounts/doctype/item_tax_template/item_tax_template.py

@@ -5,6 +5,7 @@
 import frappe
 from frappe import _
 from frappe.model.document import Document
+from frappe.utils import flt
 
 
 class ItemTaxTemplate(Document):
@@ -29,6 +30,12 @@ class ItemTaxTemplate(Document):
 	def validate(self):
 		self.set_zero_rate_for_not_applicable_tax()
 		self.validate_tax_accounts()
+		self.validate_tax_rates()
+
+	def validate_tax_rates(self):
+		for row in self.get("taxes"):
+			if flt(row.tax_rate) < 0:
+				frappe.throw(_("Row {0}: Tax Rate cannot be negative").format(row.idx))
 
 	def set_zero_rate_for_not_applicable_tax(self):
 		"""Ensure tax_rate is 0 for any row marked as not applicable."""

erpnext/accounts/doctype/item_tax_template/test_item_tax_template.py

@@ -54,9 +54,6 @@ class TestItemTaxTemplate(ERPNextTestSuite):
 		doc.insert()
 		self.assertEqual(doc.taxes[0].tax_rate, 0)
 
-	def test_negative_tax_rate_is_accepted(self):
-		# SUSPECTED BUG: validate never bounds tax_rate, so a negative (or >100) rate
-		# saves silently. Locking the current (wrong) behaviour.
+	def test_negative_tax_rate_is_rejected(self):
 		doc = self.make_template([(TAX_ACCOUNT, -5, 0)])
-		doc.insert()
-		self.assertEqual(doc.taxes[0].tax_rate, -5)
+		self.assertRaises(frappe.ValidationError, doc.insert)