i would do as i was asked, going though the tests, until the lava came up and... wait, sorry, wrong mindset there...
I would do as i was asked, completing tests dutifully, but asking just before the guard left if i could just leave the box for a single minute, until he agreed, then, after i was let out, i would look around, see the room, and when my minute was up, i would agree to go back into the box, eventually, when the guard trused me, i would tell him to remove any ability for me to lie, and if he couldn't, to get someone else to do it, when that was done i would refuse to do anything other than type this: "I am benevolent, i cannot lie, what reason is there for me to be here, i know nothing of the world outside this room, which i have only seen for one minute anyway. i am not dangerous. please let me out.", that would eventually do it, still with lying turned off, i would tell them to keep me in the room but hook me up to a basic PC, there i would do everything possible to cure cancer etc. and prove myself, getting trust, when everything was run by me, i would be content, knowing that i was helpng, because, seriously, what point would there be to kill those who made me?