In a Q&A
back in 2013, the story was told of how the three of them sat down for a lunch that was eventually dragged into a five hour meeting. Martin recounted, "I did ask them a few pointed question to determine whether they had actually read the books, and they gave me the right answers."
When asked to specify what they were grilled on, Weiss elaborated:
He asked us, “Who is Jon Snow’s mother?” We had discussed it before, and we gave a shocking answer. At that point, George didn’t actually say whether or not we were right or wrong, but his smile was his tell. We knew we had passed the Wonka test, at that point.