Messages shouldn't be modified by responding (#30)

* Test if messages are affected by responding

* Messages are copied when responding

opsdroid/message.py

@@ -1,5 +1,7 @@
 """Class to encapsulate a message."""
 
+from copy import copy
+
 
 class Message:
     # pylint: disable=too-few-public-methods
@@ -15,5 +17,6 @@ def __init__(self, text, user, room, connector):
 
     def respond(self, text):
         """Respond to this message using the connector it was created by."""
-        self.text = text
-        self.connector.respond(self)
+        response = copy(self)
+        response.text = text
+        self.connector.respond(response)

tests/test_message.py

@@ -19,4 +19,11 @@ def test_message(self):
         message.respond("Goodbye world")
 
         self.assertEqual(len(mock_connector.mock_calls), 1)
-        self.assertEqual(message.text, "Goodbye world")
+
+    def test_response_effects(self):
+        """Responding to a message shouldn't change the message."""
+        mock_connector = mock.MagicMock()
+        message_text = "Hello world"
+        message = Message(message_text, "user", "default", mock_connector)
+        message.respond("Goodbye world")
+        self.assertEqual(message_text, message.text)