Issue #8313: traceback.format_exception_only() encodes unicode message to
ASCII with backslashreplace error handler if str(value) failed
diff --git a/Lib/test/test_traceback.py b/Lib/test/test_traceback.py
index c79961e..811feac 100644
--- a/Lib/test/test_traceback.py
+++ b/Lib/test/test_traceback.py
@@ -159,6 +159,15 @@
         err = traceback.format_exception_only(None, None)
         self.assertEqual(err, ['None\n'])
 
+    def test_unicode(self):
+        err = AssertionError('\xff')
+        lines = traceback.format_exception_only(type(err), err)
+        self.assertEqual(lines, ['AssertionError: \xff\n'])
+
+        err = AssertionError(u'\xe9')
+        lines = traceback.format_exception_only(type(err), err)
+        self.assertEqual(lines, ['AssertionError: \\xe9\n'])
+
 
 class TracebackFormatTests(unittest.TestCase):