test(stock): add ledger preview unit tests (#58700)

erpnext/controllers/tests/test_ledger_preview.py

@@ -0,0 +1,23 @@
+# Copyright (c) 2026, Frappe Technologies Pvt. Ltd. and Contributors
+# See license.txt
+
+from unittest.mock import patch
+
+import frappe
+from frappe.tests import UnitTestCase
+
+from erpnext.controllers.stock_controller import get_sl_entries_for_preview
+
+
+class TestLedgerPreview(UnitTestCase):
+	def test_in_out_rate_is_only_set_for_outgoing_entries(self):
+		stock_ledger_entries = [
+			frappe._dict(actual_qty=5, stock_value_difference=10),
+			frappe._dict(actual_qty=-5, stock_value_difference=-15),
+		]
+
+		with patch("frappe.get_all", return_value=stock_ledger_entries):
+			entries = get_sl_entries_for_preview("Delivery Note", "DN-0001", [])
+
+		self.assertIsNone(entries[0].get("in_out_rate"))
+		self.assertEqual(entries[1].in_out_rate, 3)