If you want to be an online beta tester, you have to watch the release dates of games and their web sites and keep an eye out for beta signups. As for a career as a game tester, just find a way to put gaming in a resume and have a high-school diploma. I warn you its not as fun as you think, though.

Generally you wouldn't just get a demo...you'd get a beta version of a game to test and report bugs on (if online testing). They probably just got that demo from a source you haven't found yet.

Final Fantasy 7 remake (I know its not a sequel)

Age of Mythology

Bushido Blade

Final Fantasy Tactics (NONE of that Advance stuff...I want a real story, not a kids book)

Castlevania; Symphony of the Night (ALUCARD)

Ogre Battle

Tactics Ogre

I can't think...will post more later.