added new module 'chat.py'

tests/test_message.py

@@ -600,18 +600,15 @@ class MessageIDTestCase(CmmTestCase):
 class MessageHashTestCase(CmmTestCase):
     def setUp(self) -> None:
         self.message1 = Message(Question('This is a question.'),
-                                tags={Tag('tag1')},
                                 file_path=pathlib.Path('/tmp/foo/bla'))
         self.message2 = Message(Question('This is a new question.'),
                                 file_path=pathlib.Path('/tmp/foo/bla'))
         self.message3 = Message(Question('This is a question.'),
                                 Answer('This is an answer.'),
                                 file_path=pathlib.Path('/tmp/foo/bla'))
-        # message4 is a copy of message1, because only question and
-        # answer are used for hashing and comparison
+        # message4 is a copy of message1, because 'file_path'
+        # is ignored for hashing and comparison
         self.message4 = Message(Question('This is a question.'),
-                                tags={Tag('tag1'), Tag('tag2')},
-                                ai='Blabla',
                                 file_path=pathlib.Path('foobla'))
 
     def test_set_hashing(self) -> None: