Add test capturing failure. Ref #126.

Author: jaraco

testing/test_functions.py

@@ -14,6 +14,7 @@ def __format__(self, *k):
     ('1.1', '1.2.dev0'),
     ('1.2.dev', '1.2.dev0'),
     ('1.1a2', '1.1a3.dev0'),
+    ('23.24post2+deadbeef', '23.24post3.dev0'),
     ])
 def test_next_tag(tag, expected):
     version = pkg_resources.parse_version(tag)