tests: added testcases for Message.from_file() and Message.to_file()

tests/test_message.py

@@ -1,5 +1,9 @@
+from unittest import mock
+import pathlib
+from typing import cast
 from .test_main import CmmTestCase
-from chatmastermind.message import source_code, MessageError, Question, Answer
+from chatmastermind.message import source_code, Message, MessageError, Question, Answer
+from chatmastermind.tags import Tag
 
 
 class SourceCodeTestCase(CmmTestCase):
@@ -76,3 +80,42 @@ class AnswerTestCase(CmmTestCase):
         answer = Answer("No")
         self.assertIsInstance(answer, Answer)
         self.assertEqual(answer, "No")
+
+
+class TestMessage(CmmTestCase):
+
+    @mock.patch('builtins.open',
+                mock.mock_open(read_data="TAGS: tag1 tag2\n=== QUESTION ===\nThis is a question\n=== ANSWER ===\nThis is an answer"))
+    def test_from_file_txt(self) -> None:
+        file_path = pathlib.Path('message.txt')
+        with mock.patch('chatmastermind.message.pathlib.Path.exists', return_value=True):
+            message = Message.from_file(file_path)
+
+        self.assertIsInstance(message, Message)
+        self.assertEqual(message.question, 'This is a question')
+        self.assertEqual(message.answer, 'This is an answer')
+        self.assertSetEqual(cast(set[Tag], message.tags), {Tag('tag1'), Tag('tag2')})
+        self.assertEqual(message.file_path, file_path)
+
+    def test_from_file_yaml(self) -> None:
+        # TODO: Create a test yaml file
+        pass
+
+    @mock.patch('builtins.open', mock.mock_open())
+    def test_to_file_txt(self) -> None:
+        file_path = pathlib.Path('message.txt')
+        message = Message(Question('This is a question'),
+                          Answer('This is an answer'),
+                          {Tag('tag1'), Tag('tag2')},
+                          file_path)
+        message.to_file(None)
+
+        with open(file_path, "r") as fd:
+            file_contents = fd.read()
+
+        expected_contents = "TAGS: tag1 tag2\n=== QUESTION ===\nThis is a question\n=== ANSWER ===\nThis is an answer\n"
+        self.assertEqual(file_contents, expected_contents)
+
+    def test_to_file_yaml(self) -> None:
+        # TODO: Create a test yaml file
+        pass