Use mock from the standard library when available

https://docs.python.org/3/library/unittest.mock.html

requirements/test.txt

@@ -4,4 +4,4 @@ flake8
 nose
 six>=1.4.0
 PyYAML
-mock
+mock; python_version < '3.3'

test/test_functional.py

@@ -2,7 +2,10 @@
 import json
 
 import six
-import mock
+try:
+    from unittest import mock
+except ImportError:
+    import mock
 
 from ddt import ddt, data, file_data
 from nose.tools import (

tox.ini

@@ -8,14 +8,14 @@ deps =
     flake8
     six>=1.4.0
     PyYAML
-    mock
 commands = 
     nosetests -s --with-coverage --cover-package=ddt --cover-html
     flake8 ddt.py test
 
 [testenv:py27]
 deps =
     {[testenv]deps}
+    mock
     Sphinx
     sphinxcontrib-programoutput
 commands =