I\'m trying to find the best way to uncouple messageboxes from my logic so I can properly unittest it. Now I was wondering if it would be enough if I just made a seperate he
Ideally, you want the code your testing with Unit Tests to be logic and not UI. Therefore, the logic your testing shouldn't really be displaying a message box. If you are wanting to test the UI, then I would suggest Coded UI Tests.
Judging by your question, I would imagine your code shouldn't really be using a MessageBox. Perhaps instead consider using a callback or arbitrary Action, or the approaches mentioned by Luke McGregor and Sergey V.