test(sales_invoice): characterize POSService default and mode-of-payment logic

Pin the behaviour of POSService.set_pos_fields (POS-profile default
resolution and the for_validate guard) and the mode-of-payment query
helpers before refactoring them.

erpnext/accounts/doctype/sales_invoice/test_sales_invoice.py

@@ -20,6 +20,12 @@ from erpnext.accounts.doctype.purchase_invoice.test_purchase_invoice import (
 	unlink_payment_on_cancel_of_invoice,
 )
 from erpnext.accounts.doctype.sales_invoice.mapper import make_inter_company_transaction
+from erpnext.accounts.doctype.sales_invoice.services.pos import (
+	POSService,
+	get_all_mode_of_payments,
+	get_mode_of_payment_info,
+	get_mode_of_payments_info,
+)
 from erpnext.accounts.utils import PaymentEntryUnlinkError
 from erpnext.assets.doctype.asset.depreciation import post_depreciation_entries
 from erpnext.assets.doctype.asset.test_asset import create_asset
@@ -1346,6 +1352,101 @@ class TestSalesInvoice(ERPNextTestSuite):
 		self.assertEqual(pos.grand_total, 100.0)
 		self.assertEqual(pos.write_off_amount, 0)
 
+	def test_set_pos_fields_populates_invoice_from_profile(self):
+		terms = frappe.db.exists("Terms and Conditions", "_Test POS Terms")
+		if not terms:
+			terms = (
+				frappe.get_doc(
+					{
+						"doctype": "Terms and Conditions",
+						"title": "_Test POS Terms",
+						"terms": "POS terms and conditions",
+						"selling": 1,
+					}
+				)
+				.insert()
+				.name
+			)
+
+		profile = make_pos_profile()
+		profile.customer = "_Test Customer"
+		profile.tax_category = "_Test Tax Category 1"
+		profile.account_for_change_amount = "Cash - _TC"
+		profile.ignore_pricing_rule = 1
+		profile.update_stock = 1
+		profile.apply_discount_on = "Grand Total"
+		profile.tc_name = terms
+		profile.taxes_and_charges = "_Test Sales Taxes and Charges Template - _TC"
+		profile.save()
+
+		si = create_sales_invoice(do_not_save=True)
+		si.is_pos = 1
+		si.pos_profile = profile.name
+		si.customer = None
+		si.taxes = []
+
+		POSService(si).set_pos_fields(for_validate=False)
+
+		self.assertEqual(si.customer, "_Test Customer")
+		self.assertEqual(si.tax_category, "_Test Tax Category 1")
+		self.assertEqual(si.ignore_pricing_rule, 1)
+		self.assertEqual(si.account_for_change_amount, "Cash - _TC")
+		self.assertEqual(si.taxes_and_charges, "_Test Sales Taxes and Charges Template - _TC")
+		self.assertEqual(si.apply_discount_on, "Grand Total")
+		self.assertEqual(si.update_stock, 1)
+		self.assertEqual(si.terms, "POS terms and conditions")
+		self.assertTrue(si.get("payments"))
+		self.assertTrue(si.get("taxes"))
+
+	def test_set_pos_fields_for_validate_preserves_existing_values(self):
+		profile = make_pos_profile()
+		profile.tax_category = "_Test Tax Category 1"
+		profile.save()
+
+		si = create_sales_invoice(do_not_save=True)
+		si.is_pos = 1
+		si.pos_profile = profile.name
+		si.apply_discount_on = "Net Total"
+		existing_customer = si.customer
+
+		POSService(si).set_pos_fields(for_validate=True)
+
+		# for_validate must not overwrite a field the user already set
+		self.assertEqual(si.apply_discount_on, "Net Total")
+		# for_validate skips mode-of-payment fetch and profile-driven customer/tax_category
+		self.assertFalse(si.get("payments"))
+		self.assertEqual(si.customer, existing_customer)
+		self.assertFalse(si.tax_category)
+
+	def test_set_pos_fields_uses_profile_price_list_without_customer(self):
+		profile = make_pos_profile(selling_price_list="_Test Price List")
+		profile.customer = None
+		profile.save()
+
+		si = create_sales_invoice(do_not_save=True)
+		si.is_pos = 1
+		si.pos_profile = profile.name
+		si.customer = None
+
+		POSService(si).set_pos_fields(for_validate=False)
+
+		self.assertEqual(si.selling_price_list, "_Test Price List")
+
+	def test_pos_service_mode_of_payment_queries(self):
+		make_pos_profile()  # ensures a Cash mode-of-payment account for _Test Company
+		si = create_sales_invoice(do_not_save=True)
+
+		single = get_mode_of_payment_info("Cash", "_Test Company")
+		self.assertTrue(single)
+		self.assertEqual(single[0].parent, "Cash")
+
+		all_modes = get_all_mode_of_payments(si)
+		self.assertTrue(any(row.parent == "Cash" for row in all_modes))
+
+		grouped = get_mode_of_payments_info(["Cash"], "_Test Company")
+		self.assertIn("Cash", grouped)
+		self.assertEqual(grouped["Cash"].mop, "Cash")
+
 	def test_auto_write_off_amount(self):
 		make_pos_profile(
 			company="_Test Company with perpetual inventory",