diff --git a/erpnext/stock/report/cogs_by_item_group/test_cogs_by_item_group.py b/erpnext/stock/report/cogs_by_item_group/test_cogs_by_item_group.py
new file mode 100644
index 00000000000..36b9d4ad1da
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+++ b/erpnext/stock/report/cogs_by_item_group/test_cogs_by_item_group.py
@@ -0,0 +1,57 @@
+# Copyright (c) 2026, Frappe Technologies Pvt. Ltd. and Contributors
+# See license.txt
+
+import frappe
+
+from erpnext.accounts.doctype.sales_invoice.test_sales_invoice import create_sales_invoice
+from erpnext.stock.doctype.stock_entry.stock_entry_utils import make_stock_entry
+from erpnext.stock.report.cogs_by_item_group.cogs_by_item_group import execute
+from erpnext.tests.utils import ERPNextTestSuite
+
+
+class TestCogsByItemGroup(ERPNextTestSuite):
+	def run_report(self, **extra) -> list:
+		filters = frappe._dict(
+			company="_Test Company with perpetual inventory",
+			from_date="2026-01-01",
+			to_date="2026-12-31",
+		)
+		filters.update(extra)
+		return execute(filters)[1]
+
+	def test_cogs_for_item_group(self):
+		# Reuse the bootstrap item `_Test Item` (item group `_Test Item Group`).
+		# It has zero stock in `Stores - TCP1`, so this receipt starts from a clean balance.
+		item = "_Test Item"
+
+		make_stock_entry(
+			item_code=item,
+			to_warehouse="Stores - TCP1",
+			qty=10,
+			rate=100,
+			company="_Test Company with perpetual inventory",
+			posting_date="2026-06-01",
+		)
+
+		# A Sales Invoice with update_stock delivers the goods and books the COGS
+		# against the company's default expense account, which the report keys on.
+		create_sales_invoice(
+			item_code=item,
+			qty=4,
+			rate=150,
+			warehouse="Stores - TCP1",
+			company="_Test Company with perpetual inventory",
+			update_stock=1,
+			cost_center="Main - TCP1",
+			parent_cost_center="Main - TCP1",
+			debit_to="Debtors - TCP1",
+			income_account="Sales - TCP1",
+			expense_account="Cost of Goods Sold - TCP1",
+			posting_date="2026-06-02",
+		)
+
+		data = self.run_report()
+		rows = [row for row in data if "_Test Item Group" in row.get("item_group")]
+		self.assertTrue(rows, "No row found for _Test Item Group")
+		# 4 units delivered at 100 valuation rate -> 400 COGS.
+		self.assertEqual(rows[0].get("cogs_debit"), 400)