The Ideological Turing Test is an exercise where you try to pretend to hold an opposing ideology convincingly enough that outside observers can't reliably distinguish you from a true believer.
It was first described by economist Bryan Caplan:
Put me and five random liberal social science Ph.D.s in a chat room. Let liberal readers ask questions for an hour, then vote on who isn't really a liberal. Then put [economist Paul] Krugman and five random libertarian social science Ph.D.s in a chat room. Let libertarian readers ask questions for an hour, then vote on who isn't really a libertarian. Simple as that.
Passing the ideological Turing test is a sign that you understand the opposing ideology on a deep level.
The ideological Turing test has a similar motivation to Steelmanning, but works in a different way.
The name comes from the Turing Test proposed by computer scientist Alan Turing, where a computer program must pretend to be a human while human judges try to tell it apart from real humans.