travis: Introduce autopep8 test

This patch add a new test using "autopep8" to keep codes reformatted
easily by using Python tool.

Signed-off-by: IWASE Yusuke <iwase.yusuke0@gmail.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>

.travis.yml

@@ -8,6 +8,7 @@ env:
   - TOX_ENV=py35
   - TOX_ENV=pypy26
   - TOX_ENV=pycodestyle
+  - TOX_ENV=autopep8
 
 services:
   - docker

CONTRIBUTING.rst

@@ -20,19 +20,24 @@ style.
   # You can send patches by "git send-email" command
   $ git send-email --to="ryu-devel@lists.sourceforge.net" *.patch
 
-Please check your changes with pycodestyle(pep8) and run unittests to make sure
-that they don't break the existing features. The following command
-does both for you.
+Please check your changes with autopep8, pycodestyle(pep8) and running
+unit tests to make sure that they don't break the existing features.
+The following command does all for you.
 
 .. code-block:: bash
 
   # Install dependencies of tests
   $ pip install -r tools/test-requires
 
+  # Execute autopep8
+  # Also, it is convenient to add settings of your editor or IDE for
+  # applying autopep8 automatically.
+  $ autopep8 --recursive --in-place ryu/
+
   # Execute unit tests and pycodestyle(pep8)
   $ ./run_tests.sh
 
-Of course, you are encouraged to add unittests when you add new
+Of course, you are encouraged to add unit tests when you add new
 features (it's not a must though).
 
 Python version and libraries

tools/test-requires

@@ -1,3 +1,4 @@
+autopep8
 coverage
 mock
 nose

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py27,py34,py35,pypy26,pycodestyle
+envlist = py27,py34,py35,pypy26,pycodestyle,autopep8
 
 [testenv]
 deps =
@@ -38,6 +38,18 @@ deps =
 commands =
   pycodestyle
 
+[testenv:autopep8]
+# If some errors displayed with this test, please reformat codes with the
+# following command first.
+# $ autopep8 --recursive --in-place ryu/
+whitelist_externals=bash
+deps =
+  -U
+  --no-cache-dir
+  autopep8
+commands =
+  bash -c 'test -z "$(autopep8 --recursive --diff ryu/)"'
+
 [pycodestyle]
 exclude = pbr-*,.venv,.tox,.git,doc,dist,tools,vcsversion.py,.pyc,ryu/contrib
 # W503: line break occurred before a binary operator