[py3] Used six.StringIO to simulate stdout buffer in tests

tests/regressiontests/m2m_through_regress/tests.py

@@ -1,10 +1,9 @@
 from __future__ import absolute_import
 
-from io import BytesIO
-
 from django.core import management
 from django.contrib.auth.models import User
 from django.test import TestCase
+from django.utils.six import StringIO
 
 from .models import (Person, Group, Membership, UserMembership, Car, Driver,
     CarDriver)
@@ -70,11 +69,11 @@ class M2MThroughTestCase(TestCase):
 
         pks = {"p_pk": p.pk, "g_pk": g.pk, "m_pk": m.pk}
 
-        out = BytesIO()
+        out = StringIO()
         management.call_command("dumpdata", "m2m_through_regress", format="json", stdout=out)
         self.assertEqual(out.getvalue().strip(), """[{"pk": %(m_pk)s, "model": "m2m_through_regress.membership", "fields": {"person": %(p_pk)s, "price": 100, "group": %(g_pk)s}}, {"pk": %(p_pk)s, "model": "m2m_through_regress.person", "fields": {"name": "Bob"}}, {"pk": %(g_pk)s, "model": "m2m_through_regress.group", "fields": {"name": "Roll"}}]""" % pks)
 
-        out = BytesIO()
+        out = StringIO()
         management.call_command("dumpdata", "m2m_through_regress", format="xml",
             indent=2, stdout=out)
         self.assertEqual(out.getvalue().strip(), """
@@ -142,6 +141,6 @@ class ThroughLoadDataTestCase(TestCase):
 
     def test_sequence_creation(self):
         "Check that sequences on an m2m_through are created for the through model, not a phantom auto-generated m2m table. Refs #11107"
-        out = BytesIO()
+        out = StringIO()
         management.call_command("dumpdata", "m2m_through_regress", format="json", stdout=out)
         self.assertEqual(out.getvalue().strip(), """[{"pk": 1, "model": "m2m_through_regress.usermembership", "fields": {"price": 100, "group": 1, "user": 1}}, {"pk": 1, "model": "m2m_through_regress.person", "fields": {"name": "Guido"}}, {"pk": 1, "model": "m2m_through_regress.group", "fields": {"name": "Python Core Group"}}]""")