sort imports using isort. tested.

core/TESTS/tests.py

@@ -25,10 +25,11 @@ todo = '''ADD TESTS when we are redirecting /expofiles/ to a remote file-deliver
 - Add test for running cavern to produce a .3d file
 '''
 
-import unittest
 import re
+import unittest
 from http import HTTPStatus
-from django.test import TestCase, SimpleTestCase, Client
+
+from django.test import Client, SimpleTestCase, TestCase
 
 
 #class SimplePageTest(unittest.TestCase):