test(accounts): enable perpetual inventory through its cached flag

Earlier tests cache the flag as off on frappe.local, so setting it on the Company alone did not reach get_valuation_rate.

erpnext/accounts/doctype/pos_invoice_merge_log/test_pos_invoice_merge_log.py

@@ -6,6 +6,7 @@ from contextlib import contextmanager
 import frappe
 from frappe.utils import flt
 
+import erpnext
 from erpnext.accounts.doctype.coupon_code.test_coupon_code import test_create_test_data
 from erpnext.accounts.doctype.mode_of_payment.test_mode_of_payment import (
 	set_default_account_for_mode_of_payment,
@@ -37,6 +38,16 @@ def rounding_method(method):
 		frappe.local.system_settings = None
 
 
+@contextmanager
+def perpetual_inventory(company):
+	previous = erpnext.is_perpetual_inventory_enabled(company)
+	frappe.local.enable_perpetual_inventory[company] = 1
+	try:
+		yield
+	finally:
+		frappe.local.enable_perpetual_inventory[company] = previous
+
+
 def sell_over_the_counter(lines, discount_percentage=0):
 	item_code, qty, rate = lines[0]
 	sale = create_pos_invoice(item_code=item_code, qty=qty, rate=rate, do_not_save=True)
@@ -666,20 +677,18 @@ class TestPOSInvoiceMergeLog(ERPNextTestSuite):
 	def test_consolidating_standalone_return_without_stock_history(self):
 		from erpnext.stock.doctype.item.test_item import make_item
 
-		frappe.db.set_value(
-			"Company",
-			"_Test Company",
-			{"enable_perpetual_inventory": 1, "default_inventory_account": "Stock In Hand - _TC"},
-		)
+		frappe.db.set_value("Company", "_Test Company", "default_inventory_account", "Stock In Hand - _TC")
 		item_code = make_item("_Test Standalone POS Return Item", {"is_stock_item": 1}).name
 		pos_return = create_pos_invoice(item_code=item_code, qty=-1, rate=100, is_return=1, do_not_save=1)
 		pos_return.append("payments", {"mode_of_payment": "Cash", "account": "Cash - _TC", "amount": -100})
 		pos_return.paid_amount = pos_return.base_paid_amount = -100
-		self.assertRaises(frappe.ValidationError, pos_return.insert)
 
-		pos_return.items[0].incoming_rate = 80
-		pos_return.insert().submit()
-		self.make_closing_entry()
+		with perpetual_inventory("_Test Company"):
+			self.assertRaises(frappe.ValidationError, pos_return.insert)
+
+			pos_return.items[0].incoming_rate = 80
+			pos_return.insert().submit()
+			self.make_closing_entry()
 
 		pos_return.load_from_db()
 		credit_note = frappe.get_doc("Sales Invoice", pos_return.consolidated_invoice)