If you look in
debug.log, you should see a message that says "proof-of-work found".
Here is an excerpt from
debug.log for a testnet block that I found. (It was immediately orphaned; in fact an earlier block had been found several minutes earlier but had not yet reached me. So you won't find it in the blockchain.)
CBlock(hash=00000000609b21ea1d67f7220d12f7e6f06542907fa24511fa416b286e11cb54, ver=2, hashPrevBlock=00000000b96e8a2e2f27bf209a1059fd10b117cdf5a6373559eb93268853bc04, hashMerkleRoot=f25394d1360a276fa5e3c51b245969d193710d06b5bda12468e11074c8740d50, nTime=1383697696, nBits=1d00ffff, nNonce=2576125723, vtx=1)
CTransaction(hash=f25394d1360a276fa5e3c51b245969d193710d06b5bda12468e11074c8740d50, ver=1, vin.size=1, vout.size=1, nLockTime=0)
CTxIn(COutPoint(0000000000000000000000000000000000000000000000000000000000000000, 4294967295), coinbase 0330f6010101062f503253482f)
keypool keep 6
AddToWallet f25394d1360a276fa5e3c51b245969d193710d06b5bda12468e11074c8740d50 new
Committing 1 changed transactions to coin database...
SetBestChain: new best=00000000609b21ea1d67f7220d12f7e6f06542907fa24511fa416b286e11cb54 height=128560 log2_work=57.064666 tx=708022 date=2013-11-06 00:28:16 progress=1.000000
debug.log is overwritten periodically, so if your block was created some time ago, you may no longer have this entry in yours.
Newly generated coins require 100 confirmations before they can be spent, and
bitcoind apparently won't show them as spendable until 120. See also this question. As far as I know these rules are the same on testnet.
Congratulations on your newfound fake wealth!