Fix unittest if run from non-unicode shell

When opening files (like os.devnull) in text mode, python uses the shell's
default encoding. In case LANG=C or when redirecting (for example), that
is just 'ascii', so writing non-ascii strings to /dev/null fails with
UnicodeError

diff --git a/test/test_cnfvar.py b/test/test_cnfvar.py
index 2f5355a..046f56a 100755 (executable)
--- a/test/test_cnfvar.py
+++ b/test/test_cnfvar.py
@@ -412,7 +412,7 @@ class CnfVarUnittest(unittest.TestCase):
 
     def test_read_json_nonascii(self):
         cnf = cnfvar.read_cnf_json(demo_latin1crap)
-        with open(os.devnull, "w") as devnull:
+        with open(os.devnull, "wb") as devnull:
             cnfvar.print_cnf(cnf, out=devnull)
 
     def test_parse_cnf_quotes(self):