[rsgrn]

If I wanted to use mitmproxy to mitm and observe traffic during automated testing, what mode/settings should I be using on Windows?

The setup is: A client (dev machine or pipeline) running tests that communicate to a Windows VM that hosts the app under test. The client RPCs to call automation APIs on the host/server.

However I couldn't get both communicating and using mitmproxy to observe traffic to work at the same time.

[mhils]

If your server is really just one service on one port, I would just run mitmproxy as a reverse proxy and point your client to that (https://docs.mitmproxy.org/stable/concepts-modes/). If there are multiple services, having it running as a regular proxy sounds best to me.