是骡子是马，拉出来遛遛
shì​luó​zi​shì​mǎ​lā​chū​lai​liù​liu

the proof is in the pudding

是骡子是马，拉出来遛遛 是騾子是馬，拉出來遛遛 shì​luó​zi​shì​mǎ​lā​chū​lai​liù​liu
the proof is in the pudding
literally meaning "whether it is a mule or a horse, take it out for a walk"; used to express that the only way to judge someone's true ability or the quality of a thing is to put it to a practical test