Add testing extras_require, and move six to it

Author: blueyed

setup.py

@@ -33,13 +33,19 @@ def read(fname):
     install_requires=[
         'pytest>=3.6',
         'pathlib;python_version<"3.4"',
-        'six',
     ],
     extras_require={
         'docs': [
             'sphinx',
             'sphinx_rtd_theme',
-        ]
+        ],
+        'testing': [
+            'pytest>=3.6',
+            'Django',
+            'django-configurations==2.0',
+            'pytest-xdist==1.15',
+            'six',
+        ],
     },
     classifiers=['Development Status :: 5 - Production/Stable',
                  'Framework :: Django',

tox.ini

@@ -7,10 +7,8 @@ envlist =
     - py{36,py27}-checkqa
 
 [testenv]
+extras = testing
 deps =
-    pytest>=3.6
-    django-configurations==2.0
-    pytest-xdist==1.15
     {env:_PYTESTDJANGO_TOX_EXTRA_DEPS:}
 
     djmaster: https://github.com/django/django/archive/master.tar.gz