Homebrew services - how to stream its log?
The mongodb-community service logs to the following places:

$HOMEBREW_PREFIX/var/log/mongodb/mongo.log
$HOMEBREW_PREFIX/var/log/mongodb/output.log


Usually this means that they're located in:

/usr/local/var/log/mongodb/


You can continually stream the logs using a command like this in the Terminal:

tail -f /usr/local/var/log/mongodb/*.log