Vanessa Hudgens tested Zac Efron to see if he was loyal to her.

Vanessa sent “a really hot friend” to chat him up at the gym where he works out.

“He had no idea she was a friend of Vanessa’s,” says an insider involved in the scheme. “The hottie started talking to him, but Zac didn’t flirt back — and she’s gorgeous!”

Apparently Zac passed the test! Added the insider, “He’s only got eyes for Vanessa. And we had fun with the prank!”

Are they sure it was with a girl? Just saying….

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