Add 'ChessBoard::is_valid'
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384f361da2
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@ -184,4 +184,333 @@ impl ChessBoard {
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self.total_plies -= 1;
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self.side = !self.side;
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}
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/// Return true if the current state of the board looks valid, false if something is definitely
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/// wrong.
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fn is_valid(&self) -> bool {
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// Don't overlap pieces.
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for piece in Piece::iter() {
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for other in Piece::iter() {
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if piece != other {
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if !(self.piece_occupancy(piece) & self.piece_occupancy(other)).is_empty() {
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return false;
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}
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}
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}
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}
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// Don't overlap colors.
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if !(self.color_occupancy(Color::White) & self.color_occupancy(Color::Black)).is_empty() {
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return false;
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}
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// Calculate the union of all pieces.
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let combined =
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Piece::iter().fold(Bitboard::EMPTY, |board, p| board | self.piece_occupancy(p));
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// Ensure that the pre-computed version is accurate.
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if combined != self.combined_occupancy() {
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return false;
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}
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// Ensure that all pieces belong to a color, and no color has pieces that don't exist.
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if combined != (self.color_occupancy(Color::White) | self.color_occupancy(Color::Black)) {
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return false;
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}
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// Have exactly one king of each color.
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for color in Color::iter() {
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if (self.piece_occupancy(Piece::King) & self.color_occupancy(color)).count() != 1 {
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return false;
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}
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}
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// Verify that rooks and kings that are allowed to castle have not been moved.
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for color in Color::iter() {
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let castle_rights = self.castle_rights(color);
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// Nothing to check if there are no castlings allowed.
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if castle_rights == CastleRights::NoSide {
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continue;
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}
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let actual_rooks = self.piece_occupancy(Piece::Rook) & self.color_occupancy(color);
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let expected_rooks = castle_rights.unmoved_rooks(color);
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// We must check the intersection, in case there are more than 2 rooks on the board.
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if (expected_rooks & actual_rooks) != expected_rooks {
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return false;
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}
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let actual_king = self.piece_occupancy(Piece::King) & self.color_occupancy(color);
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let expected_king = Square::new(File::E, color.first_rank());
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// We have checked that there is exactly one king, no need for intersecting the sets.
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if actual_king != expected_king.into_bitboard() {
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return false;
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}
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}
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// The current en-passant target square must be empty, right behind an opponent's pawn.
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if let Some(square) = self.en_passant() {
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if !(self.combined_occupancy() & square).is_empty() {
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return false;
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}
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let opponent_pawns =
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self.piece_occupancy(Piece::Pawn) & self.color_occupancy(!self.current_player());
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let double_pushed_pawn = self
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.current_player()
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.backward_direction()
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.move_board(square.into_bitboard());
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if (opponent_pawns & double_pushed_pawn).is_empty() {
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return false;
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}
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}
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// FIXME: check for opponent being in check.
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// FIXME: check for kings touching.
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true
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}
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}
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#[cfg(test)]
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mod test {
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use super::*;
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#[test]
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fn valid() {
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let default_position = ChessBoard {
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piece_occupancy: [
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// King
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Square::E1 | Square::E8,
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// Queen
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Square::D1 | Square::D8,
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// Rook
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Square::A1 | Square::A8 | Square::H1 | Square::H8,
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// Bishop
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Square::C1 | Square::C8 | Square::F1 | Square::F8,
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// Knight
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Square::B1 | Square::B8 | Square::G1 | Square::G8,
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// Pawn
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Rank::Second.into_bitboard() | Rank::Seventh.into_bitboard(),
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],
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color_occupancy: [
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Rank::First.into_bitboard() | Rank::Second.into_bitboard(),
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Rank::Seventh.into_bitboard() | Rank::Eighth.into_bitboard(),
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],
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combined_occupancy: Rank::First.into_bitboard()
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| Rank::Second.into_bitboard()
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| Rank::Seventh.into_bitboard()
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| Rank::Eighth.into_bitboard(),
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castle_rights: [CastleRights::BothSides; 2],
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en_passant: None,
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half_move_clock: 0,
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total_plies: 0,
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side: Color::White,
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};
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assert!(default_position.is_valid());
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}
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#[test]
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fn invalid_overlapping_pieces() {
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let position = ChessBoard {
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piece_occupancy: [
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// King
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Square::E1 | Square::E8,
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// Queen
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Square::E1 | Square::E8,
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// Rook
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Bitboard::EMPTY,
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// Bishop
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Bitboard::EMPTY,
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// Knight
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Bitboard::EMPTY,
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// Pawn
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Bitboard::EMPTY,
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],
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color_occupancy: [Square::E1.into_bitboard(), Square::E8.into_bitboard()],
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combined_occupancy: Square::E1 | Square::E8,
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castle_rights: [CastleRights::NoSide; 2],
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en_passant: None,
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half_move_clock: 0,
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total_plies: 0,
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side: Color::White,
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};
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assert!(!position.is_valid());
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}
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#[test]
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fn invalid_overlapping_colors() {
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let position = ChessBoard {
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piece_occupancy: [
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// King
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Square::E1 | Square::E8,
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// Queen
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Bitboard::EMPTY,
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// Rook
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Bitboard::EMPTY,
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// Bishop
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Bitboard::EMPTY,
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// Knight
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Bitboard::EMPTY,
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// Pawn
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Bitboard::EMPTY,
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],
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color_occupancy: [Square::E1 | Square::E8, Square::E1 | Square::E8],
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combined_occupancy: Square::E1 | Square::E8,
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castle_rights: [CastleRights::NoSide; 2],
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en_passant: None,
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half_move_clock: 0,
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total_plies: 0,
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side: Color::White,
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};
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assert!(!position.is_valid());
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}
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#[test]
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fn invalid_combined_does_not_equal_pieces() {
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let position = ChessBoard {
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piece_occupancy: [
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// King
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Square::E1 | Square::E8,
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// Queen
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Bitboard::EMPTY,
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// Rook
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Bitboard::EMPTY,
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// Bishop
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Bitboard::EMPTY,
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// Knight
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Bitboard::EMPTY,
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// Pawn
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Bitboard::EMPTY,
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],
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color_occupancy: [Square::E1.into_bitboard(), Square::E8.into_bitboard()],
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combined_occupancy: Square::E1.into_bitboard(),
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castle_rights: [CastleRights::NoSide; 2],
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en_passant: None,
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half_move_clock: 0,
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total_plies: 0,
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side: Color::White,
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};
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assert!(!position.is_valid());
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}
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#[test]
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fn invalid_combined_does_not_equal_colors() {
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let position = ChessBoard {
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piece_occupancy: [
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// King
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Square::E1 | Square::E8,
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// Queen
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Bitboard::EMPTY,
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// Rook
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Bitboard::EMPTY,
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// Bishop
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Bitboard::EMPTY,
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// Knight
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Bitboard::EMPTY,
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// Pawn
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Bitboard::EMPTY,
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],
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color_occupancy: [Square::E1 | Square::H1, Square::E8 | Square::H8],
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combined_occupancy: Square::E1 | Square::E8,
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castle_rights: [CastleRights::NoSide; 2],
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en_passant: None,
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half_move_clock: 0,
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total_plies: 0,
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side: Color::White,
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};
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assert!(!position.is_valid());
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}
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#[test]
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fn invalid_multiple_kings() {
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let position = ChessBoard {
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piece_occupancy: [
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// King
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Square::E1 | Square::E2 | Square::E7 | Square::E8,
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// Queen
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Bitboard::EMPTY,
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// Rook
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Bitboard::EMPTY,
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// Bishop
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Bitboard::EMPTY,
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// Knight
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Bitboard::EMPTY,
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// Pawn
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Bitboard::EMPTY,
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],
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color_occupancy: [Square::E1 | Square::E2, Square::E7 | Square::E8],
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combined_occupancy: Square::E1 | Square::E2 | Square::E7 | Square::E8,
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castle_rights: [CastleRights::NoSide; 2],
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en_passant: None,
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half_move_clock: 0,
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total_plies: 0,
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side: Color::White,
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};
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assert!(!position.is_valid());
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}
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#[test]
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fn invalid_castling_rights_no_rooks() {
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let position = ChessBoard {
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piece_occupancy: [
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// King
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Square::E1 | Square::E8,
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// Queen
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Bitboard::EMPTY,
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// Rook
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Bitboard::EMPTY,
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// Bishop
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Bitboard::EMPTY,
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// Knight
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Bitboard::EMPTY,
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// Pawn
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Bitboard::EMPTY,
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],
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color_occupancy: [Square::E1.into_bitboard(), Square::E8.into_bitboard()],
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combined_occupancy: Square::E1 | Square::E8,
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castle_rights: [CastleRights::BothSides; 2],
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en_passant: None,
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half_move_clock: 0,
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total_plies: 0,
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side: Color::White,
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};
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assert!(!position.is_valid());
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}
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#[test]
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fn invalid_castling_rights_moved_king() {
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let position = ChessBoard {
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piece_occupancy: [
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// King
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Square::E2 | Square::E7,
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// Queen
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Bitboard::EMPTY,
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// Rook
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Square::A1 | Square::A8 | Square::H1 | Square::H8,
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// Bishop
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Bitboard::EMPTY,
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// Knight
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Bitboard::EMPTY,
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// Pawn
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Bitboard::EMPTY,
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],
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color_occupancy: [
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Square::A1 | Square::E2 | Square::H1,
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Square::A8 | Square::E7 | Square::H8,
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],
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combined_occupancy: Square::A1
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| Square::A8
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| Square::E1
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| Square::E8
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| Square::H1
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| Square::H8,
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castle_rights: [CastleRights::BothSides; 2],
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en_passant: None,
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half_move_clock: 0,
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total_plies: 0,
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side: Color::White,
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};
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assert!(!position.is_valid());
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}
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}
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