But something change in the difficult of testnet in the last hours, somebody is mining like 5 blocks per second, so if someone wants to learn how to mining they can try Testnet on this momment.
Does this mean the difficulty is very low, or, more likely, someone is mining with a massive hash rate? In your screenshot it stopped "2 minutes ago",
currently it stopped 5 minutes ago. But there are now 3356 more blocks than when you posted this (less than an hour ago).
If it's someone with very high hash rate, this doesn't mean anyone can try mining testnet now.
I tried, and even when the difficulty drops to the minimum CPU mining is futile.