diff --git a/erpnext/selling/doctype/sales_order/test_sales_order.py b/erpnext/selling/doctype/sales_order/test_sales_order.py
index a33d401..643e7cf 100644
--- a/erpnext/selling/doctype/sales_order/test_sales_order.py
+++ b/erpnext/selling/doctype/sales_order/test_sales_order.py
@@ -1064,6 +1064,7 @@
 	so.company = args.company or "_Test Company"
 	so.customer = args.customer or "_Test Customer"
 	so.currency = args.currency or "INR"
+	so.po_no = args.po_no or '12345'
 	if args.selling_price_list:
 		so.selling_price_list = args.selling_price_list
 
diff --git a/erpnext/stock/doctype/delivery_note/test_delivery_note.py b/erpnext/stock/doctype/delivery_note/test_delivery_note.py
index 0168613..9566af7 100644
--- a/erpnext/stock/doctype/delivery_note/test_delivery_note.py
+++ b/erpnext/stock/doctype/delivery_note/test_delivery_note.py
@@ -442,9 +442,15 @@
 		self.assertEqual(dn.status, "To Bill")
 		self.assertEqual(dn.per_billed, 0)
 
+		# Testing if Customer's Purchase Order No was rightly copied
+		self.assertEqual(dn.po_no, so.po_no)
+
 		si = make_sales_invoice(dn.name)
 		si.submit()
 
+		# Testing if Customer's Purchase Order No was rightly copied
+		self.assertEqual(dn.po_no, si.po_no)
+
 		dn.load_from_db()
 		self.assertEqual(dn.get("items")[0].billed_amt, 200)
 		self.assertEqual(dn.per_billed, 100)
@@ -461,16 +467,25 @@
 		si.insert()
 		si.submit()
 
+		# Testing if Customer's Purchase Order No was rightly copied
+		self.assertEqual(so.po_no, si.po_no)
+
 		frappe.db.set_value("Stock Settings", None, "allow_negative_stock", 1)
 
 		dn1 = make_delivery_note(so.name)
 		dn1.get("items")[0].qty = 2
 		dn1.submit()
 
+		# Testing if Customer's Purchase Order No was rightly copied
+		self.assertEqual(so.po_no, dn1.po_no)
+
 		dn2 = make_delivery_note(so.name)
 		dn2.get("items")[0].qty = 3
 		dn2.submit()
 
+		# Testing if Customer's Purchase Order No was rightly copied
+		self.assertEqual(so.po_no, dn2.po_no)
+
 		dn1.load_from_db()
 		self.assertEqual(dn1.get("items")[0].billed_amt, 200)
 		self.assertEqual(dn1.per_billed, 100)
@@ -492,9 +507,15 @@
 		dn1.get("items")[0].qty = 2
 		dn1.submit()
 
+		# Testing if Customer's Purchase Order No was rightly copied
+		self.assertEqual(dn1.po_no, so.po_no)
+
 		si1 = make_sales_invoice(dn1.name)
 		si1.submit()
 
+		# Testing if Customer's Purchase Order No was rightly copied
+		self.assertEqual(dn1.po_no, si1.po_no)
+
 		dn1.load_from_db()
 		self.assertEqual(dn1.per_billed, 100)
 
@@ -502,10 +523,16 @@
 		si2.get("items")[0].qty = 4
 		si2.submit()
 
+		# Testing if Customer's Purchase Order No was rightly copied
+		self.assertEqual(si2.po_no, so.po_no)
+
 		dn2 = make_delivery_note(so.name)
 		dn2.get("items")[0].qty = 5
 		dn2.submit()
 
+		# Testing if Customer's Purchase Order No was rightly copied
+		self.assertEqual(dn2.po_no, so.po_no)
+
 		dn1.load_from_db()
 		self.assertEqual(dn1.get("items")[0].billed_amt, 200)
 		self.assertEqual(dn1.per_billed, 100)
@@ -525,9 +552,15 @@
 		si = make_sales_invoice(so.name)
 		si.submit()
 
+		# Testing if Customer's Purchase Order No was rightly copied
+		self.assertEqual(so.po_no, si.po_no)
+
 		dn = make_delivery_note(si.name)
 		dn.submit()
 
+		# Testing if Customer's Purchase Order No was rightly copied
+		self.assertEqual(dn.po_no, si.po_no)
+
 		self.assertEqual(dn.get("items")[0].billed_amt, 1000)
 		self.assertEqual(dn.per_billed, 100)
 		self.assertEqual(dn.status, "Completed")