assert(relative_rank(us, to) == RANK_6);
assert(piece_on(to) == piece_of_color_and_type(us, PAWN));
assert(piece_on(from) == EMPTY);
assert(relative_rank(us, to) == RANK_6);
assert(piece_on(to) == piece_of_color_and_type(us, PAWN));
assert(piece_on(from) == EMPTY);