Use tox for tests

.travis.yml

@@ -1,9 +1,15 @@
 sudo: false
 language: python
 python:
-  - "2.7"
-  - "3.5"
+- "3.5"
+env:
+  global:
+  - PIP_RETRIES=10
+  - PIP_TIMEOUT=30
+  matrix:
+  - TOXENV=py27
+  - TOXENV=py35
 install:
-  - if [[ $TRAVIS_PYTHON_VERSION == 2.7 ]]; then pip install unittest2; fi
-  - pip install asgiref twisted autobahn
-script: if [[ $TRAVIS_PYTHON_VERSION == 2.7 ]]; then python -m unittest2; else python -m unittest; fi
+- travis_retry pip install tox
+script:
+- tox

tox.ini

@@ -0,0 +1,18 @@
+[tox]
+envlist = py{27,35}
+
+[testenv]
+usedevelop = true
+commands =
+    python -m unittest
+deps =
+    asgiref
+    twisted
+    autobahn
+
+[testenv:py27]
+commands =
+    python -m unittest2
+deps =
+    unittest2
+    {[testenv]deps}