If I suspect an opponent to use an engine, how do I report this to get it tested?

There is a  help & support forum for that. They will review the game. chances are if tou suspect someone, that others suspect him as well. and then he will get reviewed. They will normally review a game after it is complete. 

challenge the person to a 3 minute speed chess game. To test his strength. 3 minutes is not enough time to get an engine running.

if this does not hrlp, let me know. I will look up the details from when I did it.

Fred

Oddly you opened this thread. One of my opponents has a big sign on his homepage that says ACCOUNT CLOSED FOR CHEATING; yet he is playing live chess as I type this. The sign went up last night??????????????????????????????/

The icon may show that but the account has no games in Live since yesterday. Probably just a display bug or a phantom session in the database.