In the listener, if no IP addresses are supplied, we bind to 0.0.0.0. In a testing environment, we only need to bind on localhost 127.0.0.1. Binding to 0.0.0.0 invokes the OS X firewall and pops up dialogue boxes about it for every process that resmoke.py starts.

I believe that this can be fixed by setting the --bind_ip startup option to 127.0.0.1 when starting mongod and mongos.