Correct test description and add explicit encoding

Python 2 defaults to 'ascii' rather than 'utf-8 as used in Python 3, so
needs explicit setting.

test/test_ssm.py

@@ -95,12 +95,12 @@ def test_on_message(self):
         test_ssm.on_message({'empa-id': '012345'}, 'body')
 
     def test_str_bytes_outgoing(self):
-        """Test to ensure that outgoing messages are converted from Bytes to Str"""
+        """Test to ensure that incoming messages are converted from Bytes to Str"""
         test_ssm = Ssm2(self._brokers, self._msgdir, TEST_CERT_FILE,
                         self._key_path, dest=self._dest, listen=self._listen)
 
         message = "Appelle Hippocampéléphantocamélos"
-        byte_message = message.encode()
+        byte_message = message.encode('utf-8')
         test_ssm.on_message({'empa-id': '012345'}, byte_message)
 
     def test_init_expired_cert(self):