My favorite test is "Build an MTG Arena Deck in historic format around <strategy_and_or_cards> in <these_colors>. It must be exactly 60 cards and all cards must be from Arena only. Search all sets/cards currently availble on Arena, new and old".
Many times they’ll include cards that are only available in paper and/or go over the limit, and when asked to correct a mistake they'll continue to make mistakes. But recently I found that Claude is pretty damn good now at fixing its mistakes and building/optimizing decks for Arena. Asked it to make a deck based on insights it gained from my current decklist, and what it came up with was interesting and pretty fun to play.
Many times they’ll include cards that are only available in paper and/or go over the limit, and when asked to correct a mistake they'll continue to make mistakes. But recently I found that Claude is pretty damn good now at fixing its mistakes and building/optimizing decks for Arena. Asked it to make a deck based on insights it gained from my current decklist, and what it came up with was interesting and pretty fun to play.