diff --git a/tests/test_main.py b/tests/test_main.py
index c02204217..fc363ce5f 100644
--- a/tests/test_main.py
+++ b/tests/test_main.py
@@ -182,6 +182,20 @@ class TestMain(TestCase):
             _, kwargs = MockCoder.call_args
             assert kwargs["dirty_commits"] is True
 
+    @patch('aider.main.InputOutput.confirm_ask', return_value=True)
+    def test_message_file_flag(self, mock_confirm):
+        message_file_content = "This is a test message from a file."
+        message_file_path = "test_message.txt"
+        with open(message_file_path, 'w', encoding='utf-8') as message_file:
+            message_file.write(message_file_content)
+
+        with patch("aider.main.Coder.create") as MockCoder:
+            MockCoder.return_value.run = MagicMock()
+            main(["--message-file", message_file_path], input=DummyInput(), output=DummyOutput())
+            MockCoder.return_value.run.assert_called_once_with(with_message=message_file_content)
+
+        os.remove(message_file_path)
+
     def test_encodings_arg(self):
         fname = "foo.py"