test: add end-to-end procure-to-pay flow coverage

Cross-document integration tests for the purchase cycle:
- full chain: Purchase Order -> Receipt -> Invoice -> Payment, asserting
  received/billed status propagation and that outstanding clears on payment
- partial receipt and billing propagates the right percentages and status
- a submitted Purchase Order marks its source Material Request as Ordered
- a purchase return reduces the received qty on the originating order

erpnext/tests/test_procure_to_pay_flow.py

@@ -0,0 +1,92 @@
+# Copyright (c) 2026, Frappe Technologies Pvt. Ltd. and Contributors
+# See license.txt
+
+"""End-to-end procure-to-pay flow tests.
+
+These exercise the full purchase cycle across module boundaries and assert that
+quantity/billing status propagates between documents and that the money and
+stock invariants hold (outstanding cleared on payment, received qty reduced on
+return).
+"""
+
+import frappe
+from frappe.utils import flt
+
+from erpnext.accounts.doctype.payment_entry.payment_entry import get_payment_entry
+from erpnext.buying.doctype.purchase_order.mapper import make_purchase_receipt
+from erpnext.buying.doctype.purchase_order.test_purchase_order import create_purchase_order
+from erpnext.controllers.sales_and_purchase_return import make_return_doc
+from erpnext.stock.doctype.material_request.mapper import make_purchase_order
+from erpnext.stock.doctype.material_request.test_material_request import make_material_request
+from erpnext.stock.doctype.purchase_receipt.mapper import make_purchase_invoice
+from erpnext.tests.utils import ERPNextTestSuite
+
+
+class TestProcureToPayFlow(ERPNextTestSuite):
+	def test_full_chain_po_to_receipt_to_invoice_to_payment(self):
+		po = create_purchase_order(qty=10, rate=100)  # total 1000
+
+		pr = make_purchase_receipt(po.name)
+		pr.submit()
+		po.reload()
+		self.assertEqual(po.per_received, 100)
+
+		pi = make_purchase_invoice(pr.name)
+		pi.submit()
+		po.reload()
+		self.assertEqual(po.per_billed, 100)
+		self.assertEqual(flt(pi.outstanding_amount), 1000)
+
+		pe = get_payment_entry("Purchase Invoice", pi.name, bank_account="_Test Cash - _TC")
+		pe.submit()
+
+		outstanding, status = frappe.db.get_value(
+			"Purchase Invoice", pi.name, ["outstanding_amount", "status"]
+		)
+		self.assertEqual(flt(outstanding), 0)
+		self.assertEqual(status, "Paid")
+
+	def test_partial_receipt_and_billing_propagates_status(self):
+		po = create_purchase_order(qty=10, rate=100)
+
+		pr = make_purchase_receipt(po.name)
+		pr.items[0].qty = 6
+		pr.submit()
+		po.reload()
+		self.assertEqual(po.per_received, 60)
+		# still has qty left to receive and nothing billed yet
+		self.assertEqual(po.status, "To Receive and Bill")
+
+		pi = make_purchase_invoice(pr.name)
+		pi.submit()
+		po.reload()
+		self.assertEqual(po.per_billed, 60)
+
+	def test_material_request_to_purchase_order_marks_it_ordered(self):
+		mr = make_material_request(qty=10)
+
+		po = make_purchase_order(mr.name)
+		po.supplier = "_Test Supplier"
+		for item in po.items:
+			item.rate = 100
+		po.submit()
+
+		mr.reload()
+		self.assertEqual(mr.per_ordered, 100)
+		self.assertEqual(mr.status, "Ordered")
+
+	def test_purchase_return_reduces_received_qty_on_order(self):
+		po = create_purchase_order(qty=10, rate=100)
+
+		pr = make_purchase_receipt(po.name)
+		pr.submit()
+		po.reload()
+		self.assertEqual(po.per_received, 100)
+
+		return_pr = make_return_doc("Purchase Receipt", pr.name)
+		return_pr.items[0].qty = -4
+		return_pr.items[0].received_qty = -4
+		return_pr.submit()
+
+		po.reload()
+		self.assertEqual(po.per_received, 60)