Import test case classes from their public API module.

django/contrib/messages/tests/test_mixins.py

@@ -1,4 +1,4 @@
-from django.test.testcases import TestCase
+from django.test import TestCase
 from django.contrib.messages.tests.urls import ContactFormViewWithMsg
 from django.core.urlresolvers import reverse
 

tests/deprecation/tests.py

@@ -1,7 +1,7 @@
 from __future__ import unicode_literals
 import warnings
 
-from django.test.testcases import SimpleTestCase
+from django.test import SimpleTestCase
 from django.utils import six
 from django.utils.deprecation import RenameMethodsBase
 

tests/runtests.py

@@ -97,7 +97,7 @@ def get_installed():
 def setup(verbosity, test_labels):
     from django.conf import settings
     from django.db.models.loading import get_apps, load_app
-    from django.test.testcases import TransactionTestCase, TestCase
+    from django.test import TransactionTestCase, TestCase
 
     # Force declaring available_apps in TransactionTestCase for faster tests.
     def no_available_apps(self):