FA-82748 / Chess move legality / Member archive

White promotes to a black queen · case 03

After b7b8q the new piece on b8 is the lower-case (black) "q".

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

Input: {"board", "moves": [uci strings]}. Apply the moves in order and return the final board sorted by square. A king moving two files castles: the rook jumps from h to f (g-file destination) or from a to d (c-file destination). A pawn moving diagonally onto an empty square captures en passant, removing the pawn on the destination file and origin rank. A fifth character promotes to that piece in the mover's colour.

Why this case matters

Move application defines the position every later legality check sees.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
white promotion	`{"b8": "q", "e1": "K", "e8": "k"}`	`{"b8": "Q", "e1": "K", "e8": "k"}`	Failed

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