You two are wrong. "Testify" comes from the Latin "witness" and has nothing to do with "testicle" which also comes from the Latin for "witness". I was asked this in class by the professor in college English. I would have been wrong and embarrassed myself, so I just said "I don't know". But here's what I got from the Internet:
testatio -onis f. calling to witness , or bearing witness.

testificatio -onis f. bearing witness , testifying; evidence, proof.

testificor -ari dep. to bear witness to , give evidence of; to show, bring to light; to call to witness.

testimonium -i n. witness , evidence; proof, indication.

testis (1) -is c. one who gives evidence , a witness; an eye-witness, a spectator.

testor -ari dep. (1) to bear witness to , give evidence of; to make known, publish, declare; as pass. to be attested, declared. (2) to make a will. (3) to call to witness.

BTW they are called "testicles" because they WITNESS to the procreative power of a man.

1. To give one's information "as truthfully as possible." Taken from an old Roman phrase "to swear on one's testicles." Now, think about that, and think about how differently court cases would turn out if that meaning held true to this day...

A greeting or callback created for the Repo Army (fan-base) for 'Repo! The Genetic Opera', a film written and directed by Darren Lynn Bousman. It is similar to the "ribbit" callback for 'The Devil's Carnival'.

To attend a religious revival event, during which you would be prompted by the preacher to testify.

The act of testifying normally involves babbling incoherently while sharing folksy stories of your nasty life being turned around because the creator of the universe decided to pay you a personal visit and issue a get out of jail free card. He's nice like that, and as a pensioner he has a free bus pass allowing him to travel anywhere in the world.

When your testicles are being touched

the testifyer is given when the man squats over the womans asshole while she lays on her back with the legs above her, near her head. The balls and cock are inserted into the womans fuck holes and then are "pumped" multiple times.

To defile an object or area with your testicles.

To snitch

Testify means lot's of things. It can be said almost in any situation. Nancy Grace is a fan of Testification. Testifying can mean you're trying to receive some justice (see receiving justice for more info). You're hitting on someone. You're trying to get laid. You're trying to tell someone what the fuck is up. You're trying to get belligerent drunk. You're trying this, trying that. Ect.