Which testnet am I on? How can I know which testnet am I on?

I just ran bitcoind -testnet, and I would assume it would connect to the most recent one, but is there a way to know it?
Bitcoin and bitcoind versions v0.3.14 - v0.3.19 used the first testnet.
Bitcoin, Bitcoin-Qt and bitcoind versions v0.3.20 - v0.6.1 used the second testnet.
Bitcoin-Qt and bitcoind version v0.7.0 and above use the third testnet.