The Trickery Domain cleric gets the Channel Divinity: Invoke Duplicity feature at 2nd level, which creates "a perfect illusion of yourself" (PHB p.63).
However, CD:ID's description doesn't really tell us anything about what this illusory double actually does while it lasts (does it mimic its originator's actions, or does it act independently?), nor do the rules tell us whether this duplicate can be revealed to be an illusion -- using an Intelligence (Investigation) test, perhaps, or via a physical attack? -- and if it can be, what happens if someone "sees through it".
Have I missed something, or are the answers completely up to the DM? (I think the latter is perfectly fine, btw, just don't want to houserule something that's covered officially.)