Use unittest-mixins instead of coverage.test_helpers

Author: nedbat

tests/plugin_test.py

@@ -8,9 +8,9 @@
 import re
 import unittest
 
-import coverage
-from coverage.test_helpers import TempDirMixin
+from unittest_mixins import StdStreamCapturingMixin, TempDirMixin
 
+import coverage
 import django
 from django.conf import settings
 

tox.ini

@@ -21,6 +21,7 @@ envlist =
 
 [testenv]
 deps =
+    unittest-mixins==1.0
     django14: Django >=1.4, <1.5
     django15: Django >=1.5, <1.6
     django16: Django >=1.6, <1.7