'Test major, minor, and patch-level differences.'

def test_levels(self):

    self.assertEqual(version_diff('1', '2'), (-1), 'Major    version    diff    (no    minor)')
    self.assertEqual(version_diff('1.0', '2.0'), (-1), 'Major    version    diff    (matching    minor)')
    self.assertEqual(version_diff('0.1', '0.2'), (-1), 'Minor    version    diff    (no    patch)')
    self.assertEqual(version_diff('0.1.0', '0.2.0'), (-1), 'Minor    version    diff    (matching    patch)')
    self.assertEqual(version_diff('0.0.1', '0.0.2'), (-1), 'Patch    version    diff    (no    sub-patch)')
    self.assertEqual(version_diff('0.0.1.0', '0.0.2.0'), (-1), 'Patch    version    diff    (matching    sub-patch)')
