Yes it's being run on the testnet, I have no other nodes running.
I have no firewalls as far as I know, I'm running Ubuntu with default settings and I even tried disabling ufw.
I configured the config file to according to the book "Mastering bitcoin" as so:

rpcuser=bitcoinrpc
rpcpassword=(arbitrary digits I chose)

I'm using an external harddrive as datadir.
Btw, when using an external hdd as datadir I have to run bitcoind as sudo for it to work.
I'm downloading the testnet to my internal datadir as I'm writing this message, don't know if it will fit though.
I haven't tried the mainnet because the blockchain is to big for my internal hdd.