chess/tests/unit/pieces/King.test.js

/**
 * @jest-environment jsdom
 * King piece comprehensive tests - includes castling, check evasion, and movement restrictions
 */

import { King } from '../../../js/pieces/King.js';
import { Board } from '../../../js/game/Board.js';

describe('King', () => {
  let board;

  beforeEach(() => {
    board = new Board();
    board.clear();
  });

  describe('One Square Movement', () => {
    test('king can move one square in any direction', () => {
      const king = new King('white', { row: 4, col: 4 });
      board.setPiece(4, 4, king);

      const moves = king.getValidMoves(board);

      const expectedMoves = [
        { row: 3, col: 3 }, { row: 3, col: 4 }, { row: 3, col: 5 },
        { row: 4, col: 3 }, /* king here */ { row: 4, col: 5 },
        { row: 5, col: 3 }, { row: 5, col: 4 }, { row: 5, col: 5 }
      ];

      expect(moves).toHaveLength(8);
      expectedMoves.forEach(expected => {
        expect(moves).toContainEqual(expected);
      });
    });

    test('king in corner has 3 moves', () => {
      const king = new King('white', { row: 0, col: 0 });
      board.setPiece(0, 0, king);

      const moves = king.getValidMoves(board);

      expect(moves).toHaveLength(3);
      expect(moves).toContainEqual({ row: 0, col: 1 });
      expect(moves).toContainEqual({ row: 1, col: 0 });
      expect(moves).toContainEqual({ row: 1, col: 1 });
    });

    test('king on edge has 5 moves', () => {
      const king = new King('white', { row: 0, col: 4 });
      board.setPiece(0, 4, king);

      const moves = king.getValidMoves(board);

      expect(moves).toHaveLength(5);
    });

    test('king cannot move two squares (except castling)', () => {
      const king = new King('white', { row: 4, col: 4 });
      board.setPiece(4, 4, king);

      const moves = king.getValidMoves(board);

      // No move should be more than 1 square away
      moves.forEach(move => {
        const rowDiff = Math.abs(move.row - 4);
        const colDiff = Math.abs(move.col - 4);
        expect(rowDiff).toBeLessThanOrEqual(1);
        expect(colDiff).toBeLessThanOrEqual(1);
      });
    });
  });

  describe('Cannot Move Into Check', () => {
    test('king cannot move into attacked square', () => {
      const whiteKing = new King('white', { row: 7, col: 4 });
      const blackRook = { type: 'rook', color: 'black', position: { row: 0, col: 5 } };

      board.setPiece(7, 4, whiteKing);
      board.setPiece(0, 5, blackRook);

      const moves = whiteKing.getValidMoves(board, board);

      // Cannot move to (7,5) or (6,5) - attacked by rook
      expect(moves).not.toContainEqual({ row: 7, col: 5 });
      expect(moves).not.toContainEqual({ row: 6, col: 5 });
    });

    test('king cannot move adjacent to opponent king', () => {
      const whiteKing = new King('white', { row: 4, col: 4 });
      const blackKing = { type: 'king', color: 'black', position: { row: 4, col: 6 } };

      board.setPiece(4, 4, whiteKing);
      board.setPiece(4, 6, blackKing);

      const moves = whiteKing.getValidMoves(board, board);

      // Cannot move to (4,5) - adjacent to black king
      expect(moves).not.toContainEqual({ row: 4, col: 5 });
      expect(moves).not.toContainEqual({ row: 3, col: 5 });
      expect(moves).not.toContainEqual({ row: 5, col: 5 });
    });
  });

  describe('Castling - Kingside', () => {
    test('king can castle kingside when conditions met', () => {
      const king = new King('white', { row: 7, col: 4 });
      const rook = { type: 'rook', color: 'white', position: { row: 7, col: 7 }, hasMoved: false };

      board.setPiece(7, 4, king);
      board.setPiece(7, 7, rook);

      const gameState = { castlingRights: { whiteKingside: true } };
      const moves = king.getValidMoves(board, board, gameState);

      expect(moves).toContainEqual({ row: 7, col: 6, castling: 'kingside' });
    });

    test('cannot castle if king has moved', () => {
      const king = new King('white', { row: 7, col: 4 });
      king.hasMoved = true;
      const rook = { type: 'rook', color: 'white', position: { row: 7, col: 7 }, hasMoved: false };

      board.setPiece(7, 4, king);
      board.setPiece(7, 7, rook);

      const gameState = { castlingRights: { whiteKingside: false } };
      const moves = king.getValidMoves(board, board, gameState);

      expect(moves).not.toContainEqual({ row: 7, col: 6, castling: 'kingside' });
    });

    test('cannot castle if rook has moved', () => {
      const king = new King('white', { row: 7, col: 4 });
      const rook = { type: 'rook', color: 'white', position: { row: 7, col: 7 }, hasMoved: true };

      board.setPiece(7, 4, king);
      board.setPiece(7, 7, rook);

      const gameState = { castlingRights: { whiteKingside: false } };
      const moves = king.getValidMoves(board, board, gameState);

      expect(moves).not.toContainEqual({ row: 7, col: 6, castling: 'kingside' });
    });

    test('cannot castle through pieces', () => {
      const king = new King('white', { row: 7, col: 4 });
      const rook = { type: 'rook', color: 'white', position: { row: 7, col: 7 }, hasMoved: false };
      const bishop = { type: 'bishop', color: 'white', position: { row: 7, col: 5 } };

      board.setPiece(7, 4, king);
      board.setPiece(7, 7, rook);
      board.setPiece(7, 5, bishop);

      const gameState = { castlingRights: { whiteKingside: true } };
      const moves = king.getValidMoves(board, board, gameState);

      expect(moves).not.toContainEqual({ row: 7, col: 6, castling: 'kingside' });
    });

    test('cannot castle through check', () => {
      const king = new King('white', { row: 7, col: 4 });
      const rook = { type: 'rook', color: 'white', position: { row: 7, col: 7 }, hasMoved: false };
      const blackRook = { type: 'rook', color: 'black', position: { row: 0, col: 5 } };

      board.setPiece(7, 4, king);
      board.setPiece(7, 7, rook);
      board.setPiece(0, 5, blackRook);

      const gameState = { castlingRights: { whiteKingside: true } };
      const moves = king.getValidMoves(board, board, gameState);

      expect(moves).not.toContainEqual({ row: 7, col: 6, castling: 'kingside' });
    });

    test('cannot castle while in check', () => {
      const king = new King('white', { row: 7, col: 4 });
      const rook = { type: 'rook', color: 'white', position: { row: 7, col: 7 }, hasMoved: false };
      const blackRook = { type: 'rook', color: 'black', position: { row: 0, col: 4 } };

      board.setPiece(7, 4, king);
      board.setPiece(7, 7, rook);
      board.setPiece(0, 4, blackRook);

      const gameState = { castlingRights: { whiteKingside: true }, inCheck: true };
      const moves = king.getValidMoves(board, board, gameState);

      expect(moves).not.toContainEqual({ row: 7, col: 6, castling: 'kingside' });
    });
  });

  describe('Castling - Queenside', () => {
    test('king can castle queenside when conditions met', () => {
      const king = new King('white', { row: 7, col: 4 });
      const rook = { type: 'rook', color: 'white', position: { row: 7, col: 0 }, hasMoved: false };

      board.setPiece(7, 4, king);
      board.setPiece(7, 0, rook);

      const gameState = { castlingRights: { whiteQueenside: true } };
      const moves = king.getValidMoves(board, board, gameState);

      expect(moves).toContainEqual({ row: 7, col: 2, castling: 'queenside' });
    });
  });
});