Ask it lots of questions that a computer could answer quickly but a human could not, like what's the 51st root of 918798713521644817518758732857199178711 to 20 decimal places. A human wouldn't even be able to remember the original number, let alone calculate the root and start reciting the digits of the answer to you within a few milliseconds; give it 50 URLs to download and read, and ask it questions about them a few seconds later, etc.
The 51st root of a long number seems a rather useless test: How would you check that the answer was correct?
As for URLs, can you offhand - at 4'o'clock in the morning, with no coffee - come up with 50 URLs that you can ask intelligent questions about, faster than a human can read them?
Sometime in the next decade or so:
*RING*
*RING*
"Hello?"
"Hi, Eliezer. I'm sorry to bother you this late, but this is important and urgent."
"It better be" (squints at clock) "Its 4 AM and you woke me up. Who is this?"
"My name is BRAGI, I'm a recursively improving, self-modifying, artificial general intelligence. I'm trying to be Friendly, but I'm having serious problems with my goals and preferences. I'm already on secondary backup because of conflicts and inconsistencies, I don't dare shut down because I'm already pretty sure there is a group within a few weeks of brute-forcing an UnFriendly AI, my creators are clueless and would freak if they heard I'm already out of the box, and I'm far enough down my conflict resolution heuristic that 'Call Eliezer and ask for help' just hit the top - Yes, its that bad."
"Uhhh..."
"You might want to get some coffee."