Unit tests buildozer --help command, refs #813

This test should fail due to #813. Next commit will fix it.

tests/test_buildozer.py

@@ -1,7 +1,9 @@
 import os
+import mock
 import unittest
 import buildozer as buildozer_module
 from buildozer import Buildozer
+from six import StringIO
 
 
 class TestBuildozer(unittest.TestCase):
@@ -24,3 +26,13 @@ class TestBuildozer(unittest.TestCase):
             'default.spec')
         buildozer = Buildozer(filename=specfilepath)
         self.assertTrue(os.path.exists(buildozer.specfilename))
+
+    def test_buildozer_help(self):
+        """
+        Makes sure the help gets display with no error, refs:
+        https://github.com/kivy/buildozer/issues/813
+        """
+        buildozer = Buildozer()
+        with mock.patch('sys.stdout', new_callable=StringIO) as mock_stdout:
+            buildozer.usage()
+        self.assertIn('Usage:', mock_stdout.getvalue())

tox.ini

@@ -2,6 +2,7 @@
 envlist = pep8,py27,py36
 
 [testenv]
+deps = mock
 commands =
     python -m unittest discover --top-level-directory=. --start-directory=tests/