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.
Since I was a witness to the crime, they want me to testify in court.

by Carey1234 November 2, 2008
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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...
"Testify" is usually used in reference to a court setting or a confession of some sort.
by aka_Pyro June 27, 2007
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To defile an object or area with your testicles.
That nekid dude just testified Boomhauer's forehead. See also, teabaggin'.
by don nalgotas August 16, 2005
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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'.
Person#1: This is Sarah. She's starting a shadow cast
Persons#2, #3: Testify!
by lolzitsme March 12, 2012
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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.
Peter Popoff: Testify brother!
Hick: Well, I dun gone crashed mah car while drunk, and then I cheated on my sister with mah cousin. I's a sinner, but the baby Jesus came in to mah trailer and fixed me up good. Now I 'aint feelin' no guilt when I'm porking mah cousin.
by DairyGod June 22, 2009
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