[1.8.x] Sorted imports with isort; refs #23860.

Backport of 0ed7d15563 from master

tests/check_framework/tests.py

@@ -1,21 +1,22 @@
 # -*- coding: utf-8 -*-
 from __future__ import unicode_literals
 
-from django.utils.six import StringIO
 import sys
 
 from django.apps import apps
 from django.conf import settings
 from django.core import checks
 from django.core.checks import Error, Warning
+from django.core.checks.compatibility.django_1_7_0 import \
+    check_1_7_compatibility
 from django.core.checks.registry import CheckRegistry
-from django.core.checks.compatibility.django_1_7_0 import check_1_7_compatibility
-from django.core.management.base import CommandError
 from django.core.management import call_command
+from django.core.management.base import CommandError
 from django.db import models
 from django.test import TestCase
 from django.test.utils import override_settings, override_system_checks
 from django.utils.encoding import force_text
+from django.utils.six import StringIO
 
 from .models import SimpleModel