you don't need to install tox in tox virtualenv, but in your host env, you do

brunobord · brunobord · commit 64199a6da29d · 2016-09-08T16:12:04.000+02:00
diff --git a/requirements_dev.txt b/requirements_dev.txt
@@ -2,3 +2,4 @@
 bumpversion==0.5.3
 wheel==0.29.0
 sphinx>=1.4.6
+tox>=1.7.0
diff --git a/requirements_test.txt b/requirements_test.txt
@@ -1,6 +1,5 @@
 -r requirements.txt
 coverage==4.1
 mock>=1.0.1
-tox>=1.7.0
 psycopg2>=2.6.2
 dj_database_url>=0.4.1
