test: add coverage for COGS By Item Group report

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

erpnext/stock/report/cogs_by_item_group/test_cogs_by_item_group.py

@@ -0,0 +1,67 @@
+# 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.item.test_item import make_item
+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):
+		frappe.get_doc(
+			{
+				"doctype": "Item Group",
+				"item_group_name": "_Test COGS Group",
+				"parent_item_group": "All Item Groups",
+				"is_group": 0,
+			}
+		).insert(ignore_if_duplicate=True)
+
+		item = make_item(
+			properties={"is_stock_item": 1, "is_sales_item": 1, "item_group": "_Test COGS Group"}
+		).name
+
+		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 COGS Group" in row.get("item_group")]
+		self.assertTrue(rows, "No row found for _Test COGS Group")
+		# 4 units delivered at 100 valuation rate -> 400 COGS.
+		self.assertEqual(rows[0].get("cogs_debit"), 400)