I'm mining Testnet now! It's CPU only, on a server. Let's see if it catches a block.
It's been 4 days, and at 6.33Mh/s, I haven't found a single block. Maybe I did something wrong, or maybe CPU mining is still too slow even when the difficulty is 1. Either way, I gave up for now, and killed the miner. It seems like a waste of CPU. I'll keep Bitcoin Core Testnet running for a while.
If you use bitcoind or CLI environment, did you check whether you actually mine block but become stale?
As far as I could see, I never mined a block.
Based on these posts, did you try to mine tBTC on a month without any result? IIRC my GPU has speed about 200 Mh/s, so you should already mine at least a block within a month.