Ensure tests actually generate expected failures (#47)

tests/auth.py

diff --git a/tests/auth.py b/tests/auth.py
index 021cda7..9d6e9c3 100644
--- a/tests/auth.py
+++ b/tests/auth.py
@@ -39,6 +39,10 @@
     """convert arbitrary string to fullmatch regex"""
     return re.escape(s) + '$'
 
+def _string_to_re(s):
+    """convert arbitrary string to fullmatch regex"""
+    return re.escape(s) + '$'
+
 @pytest.mark.auth
 async def test_auth_basics():
     app = asfquart.construct("foobar", token_file=None)