Why on gods earth would someone name a prod db xxx_Test?!

maybe the same logic of people that keep important files on the trash. I'm not even joking...

Maybe it's an adult site?

The OP propably meant "xxx" as in anything, eg "why would someone name a prod db with a name ending in _Test".

And probably, its just because the administrator forgot to change the name when moving from test to prod. And now its too difficult to change the name, like many scripts and configs to change.

Its just a name. It don't matter->.

@sebastian correct. It shouldn't matter except they also have xxx and xxx_dev on the same server...