The vIt 'Iw tay ritual is a Klingon ceremony where a being whose biological origins are in doubt is cut by six different warriors using their own d'k tahgs to prove that the being in question is Klingon.
The ritual was created by the Klingon High Council shortly after Imperial Intelligence began surgically altering Klingons for spying purposes and the Council was worried that their enemies would be doing the same.
The vIt 'Iw tay was forcibly performed several times during the Dominion War, but no Changelings were ever found this way.
In 2379, it was discovered that Emperor Kahless had been replaced by a hologram. Upon his return, Kahless was ordered to undergo the ritual to convince people that he was indeed real. The ritual was performed by Chancellor Martok, three other members of the High Council, Captain Wovogh, and a commoner chosen at random. (TNG novel: A Time for War, A Time for Peace)