Kate Upton's Bra -- HOLDING ON FOR DEAR LIFE!!

Kate Upton's bra was battle tested yesterday ... pushed to its ultimate limits ... and unfortunately for us, it emerged victorious.

Kate was hangin' out on the set of "The Other Woman" in Westhampton, NY ... when for some glorious reason, she began to jump around ... bouncing ... and bouncing ... and bouncing some more.

In the end, the bra -- like anyone else in its position -- refused to surrender its grip.