Switch to tox for unit test execution.

Author: johnthagen

.coveragerc

@@ -0,0 +1,5 @@
+[run]
+branch = True
+omit =
+    .tox/*
+    setup.py

.travis.yml

@@ -1,16 +1,21 @@
 language: python
+
+# Python 3.5 specified to make tox environment 'py35' work.
+# See: https://github.com/travis-ci/travis-ci/issues/4794
 python:
   - 3.5
-  - 3.4
-  - 3.3
-  - 2.7
+
+# Environment changes have to be manually synced with 'tox.ini'.
+# See: https://github.com/travis-ci/travis-ci/issues/3024
+env:
+  - TOXENV=py27
+  - TOXENV=py33
+  - TOXENV=py34
+  - TOXENV=py35
+  - TOXENV=pypy
+
 install:
-  - pip install -r requirements.txt
-  - pip install codecov
-  - pip install flake8 pep8-naming flake8-quotes flake8-import-order
-before_script:
-  flake8 --max-line-length=99 --import-order-style=google
+  - pip install tox
+
 script:
-  python -Werror -m coverage run test.py
-after_success:
-  codecov
+  tox

requirements-dev.txt

@@ -0,0 +1,6 @@
+flake8<3.0.0
+pep8-naming
+flake8-quotes
+flake8-import-order
+pytest
+pytest-cov

requirements.txt

@@ -1,2 +1,2 @@
-exitstatus
+exitstatus>1.0.0
 typing

test.py

@@ -130,6 +130,3 @@ def write(self, s):    # type: (str) -> None
 
             sys.stderr = NullWriter()
             parse_arguments()
-
-if __name__ == '__main__':
-    unittest.main()

tox.ini

@@ -0,0 +1,25 @@
+[tox]
+# Environment changes have to be manually synced with '.travis.yml'.
+envlist =
+    py27
+    py33
+    py34
+    py35
+    pypy
+
+[flake8]
+max-line-length = 99
+import-order-style = google
+
+[testenv]
+passenv = CI TRAVIS_BUILD_ID TRAVIS TRAVIS_BRANCH TRAVIS_JOB_NUMBER TRAVIS_PULL_REQUEST TRAVIS_JOB_ID TRAVIS_REPO_SLUG TRAVIS_COMMIT
+deps =
+    -rrequirements-dev.txt
+    codecov
+
+commands =
+    flake8
+    # Ignore DeprecationWarning / PendingDeprecationWarning triggered by tox/virtualenv
+    python -bb -Werror -Wignore::DeprecationWarning -Wignore::PendingDeprecationWarning \
+        -m pytest --cov=./ test.py
+    codecov -e TOXENV