added 'message_in()' function and test

tests/test_message.py

@@ -2,7 +2,7 @@ import pathlib
 import tempfile
 from typing import cast
 from .test_main import CmmTestCase
-from chatmastermind.message import source_code, Message, MessageError, Question, Answer, AILine, ModelLine, MessageFilter
+from chatmastermind.message import source_code, Message, MessageError, Question, Answer, AILine, ModelLine, MessageFilter, message_in
 from chatmastermind.tags import Tag, TagLine
 
 
@@ -761,3 +761,17 @@ class MessageFilterTagsTestCase(CmmTestCase):
         self.assertSetEqual(tags_pref, {Tag('atag1')})
         tags_cont = self.message.filter_tags(contain='2')
         self.assertSetEqual(tags_cont, {Tag('btag2')})
+
+
+class MessageInTestCase(CmmTestCase):
+    def setUp(self) -> None:
+        self.message1 = Message(Question('This is a question.'),
+                                tags={Tag('atag1'), Tag('btag2')},
+                                file_path=pathlib.Path('/tmp/foo/bla'))
+        self.message2 = Message(Question('This is a question.'),
+                                tags={Tag('atag1'), Tag('btag2')},
+                                file_path=pathlib.Path('/tmp/bla/foo'))
+
+    def test_message_in(self) -> None:
+        self.assertTrue(message_in(self.message1, [self.message1]))
+        self.assertFalse(message_in(self.message1, [self.message2]))