test: created a new user to test child perms (#24943)

Co-authored-by: Sagar Vora <sagar@resilient.tech>
diff --git a/erpnext/selling/doctype/sales_order/test_sales_order.py b/erpnext/selling/doctype/sales_order/test_sales_order.py
index ee16f44..2eff80d 100644
--- a/erpnext/selling/doctype/sales_order/test_sales_order.py
+++ b/erpnext/selling/doctype/sales_order/test_sales_order.py
@@ -1,11 +1,12 @@
 # Copyright (c) 2015, Frappe Technologies Pvt. Ltd. and Contributors
 # License: GNU General Public License v3. See license.txt
 from __future__ import unicode_literals
-import frappe
 import json
-from frappe.utils import flt, add_days, nowdate
-import frappe.permissions
 import unittest
+import frappe
+import frappe.permissions
+from frappe.utils import flt, add_days, nowdate
+from frappe.core.doctype.user_permission.test_user_permission import create_user
 from erpnext.selling.doctype.sales_order.sales_order \
 	import make_material_request, make_delivery_note, make_sales_invoice, WarehouseRequired
 from erpnext.stock.doctype.stock_entry.stock_entry_utils import make_stock_entry
@@ -444,10 +445,8 @@
 	def test_update_child_perm(self):
 		so = make_sales_order(item_code= "_Test Item", qty=4)
 
-		user = 'test@example.com'
-		test_user = frappe.get_doc('User', user)
-		test_user.add_roles("Accounts User")
-		frappe.set_user(user)
+		test_user = create_user("test_so_child_perms@example.com", "Accounts User")
+		frappe.set_user(test_user.name)
 
 		# update qty
 		trans_item = json.dumps([{'item_code' : '_Test Item', 'rate' : 200, 'qty' : 7, 'docname': so.items[0].name}])
@@ -456,18 +455,14 @@
 		# add new item
 		trans_item = json.dumps([{'item_code' : '_Test Item', 'rate' : 100, 'qty' : 2}])
 		self.assertRaises(frappe.ValidationError, update_child_qty_rate,'Sales Order', trans_item, so.name)
-		test_user.remove_roles("Accounts User")
-		frappe.set_user("Administrator")
 
 	def test_update_child_qty_rate_with_workflow(self):
 		from frappe.model.workflow import apply_workflow
 
-		frappe.set_user("Administrator")
 		workflow = make_sales_order_workflow()
 		so = make_sales_order(item_code= "_Test Item", qty=1, rate=150, do_not_submit=1)
 		apply_workflow(so, 'Approve')
 
-		frappe.set_user("Administrator")
 		user = 'test@example.com'
 		test_user = frappe.get_doc('User', user)
 		test_user.add_roles("Sales User", "Test Junior Approver")