After the conversion is complete, you can start a local server with the new map.
$ test/start_server {xp2_file}
Then join it with an XPilot client.
$ xpilot -join localhost -port 15346
When you're done testing, press ctrl+c to stop the server. If you already had a server running on the port 15346, I probably don't need to tell you what to modify in the start script.