Indeed... I remember the time where you could just spin up a testnet node and run cpuminer with one or two threads to solomine tBTC, but as it stands now, the diff was pushed to 10.5M with a block reward of only 0.39 tBTC/block. The time between 2 blocks is often ~20 minutes tough (at which point the diff drops to 1 for the next block), telling me that the person who pushed so much hashrate on the test network has since turned of his ASIC.
That being said, there's still somebody with an ASIC that's being active on the testnet, since i've tried mining with my geckoscience stick and my server (8 threads, old XEON's) and i can't hit a single block, so even at diff 1, somebody is hashing at such speeds they beat me to a diff 1 valid block long before my cpu or stickminer finds a valid block at diff 1.

10.5M means that somebody was mining with about 75 Th, it also means that an "old" S7 (for example) would generate:
(((((Hashrate (hashes/sec) * average block reward * 600 * 65535) / 2^48) / Difficulty) * 6 * 24)
(((((4700000000000‬ * 0.39 * 600 * 65535) / 2^48) / 10500000) * 6 * 24) = 3.51 tBTC/day

This while burning 1.25 KWatt * 24 hours * 0.3€/kwh = 9€/day

So, if you have an old S7, and you run it 24/7, 1tBTC would cost you ~2.6 euro's to mine because somebody tought it was funny to mine with a total hashrate of 75 Th...

I, for one, would applaud resetting the testnet once again... Hopefully this time people won't push the diff to such heights... It's a testnet for pete's sake... It's worthless, the dev's can pull the plug at any moment... I can't imagine why anybody would want to push the diff to a height where a simple dev can't just solo cpu mine some tBTC when he needs to test something...