Game of Life in 50 lines and 20 specs

game.js

// http://en.wikipedia.org/wiki/Conway's_Game_of_Life

var Game = {

    init: function (options) {
        this.grid = new Grid(options);
    },

    putCell: function (x, y, state) {
        this.grid.putCell(x, y, state);
    },

    getCell: function (x, y) {
        return this.grid.getCell(x, y);
    },

    nextStep: function () {
        var cells = this.grid.allCells();

        _.each(cells, function(currentCell) {
            var neighboursCount = getNeighboursCountFor(currentCell, cells);

            var nextCellState = getNextCellState(currentCell, neighboursCount);
            currentCell.cell.setStateTo(nextCellState);
        });

        function getNeighboursCountFor(currentCell, cells) {
            var neighboursCells = _.filter(cells, function (otherCell) {
                
                return isCloseTo(currentCell, otherCell);

                function isCloseTo(currentCell, otherCell) {
                    var yDistance = otherCell.y - currentCell.y;
                    var xDistance = otherCell.x - currentCell.x;

                    return (yDistance !== 0 || xDistance !== 0) && (yDistance >= 1 || xDistance >= 1);
                }
            });

            return neighboursCells.length;
        }

        function getNextCellState(currentCell, neighboursCount) {
            if (currentCell.cell.state === CellState.Dead && neighboursCount === 3) {
                return CellState.Live;
            } else if (neighboursCount < 2 || neighboursCount >= 3) {
                return CellState.Dead;
            }

            return currentCell.cell.state;
        }
    }
};

game.spec.js

describe('game spec', function () {

    describe('when game is initialing', function () {

        beforeEach(function () {
            Game.init();
        });

        it ('should create game field', function () {
            expect(Game.grid).toBeDefined();
        });

    });

    describe('when game is constructing with options', function () {

        beforeEach(function () {
            Game.init({ height: 4, width: 14});
        });

        it ('should create game field with dimentions', function () {
            expect(Game.grid.height).toEqual(4);
            expect(Game.grid.width).toEqual(14);
        });

    });

    describe('when cell are placed on game', function () {

        beforeEach(function () {
            Game.init({ height: 4, width: 4});
            Game.putCell(0, 2);
        });

        it ('should field have corresponding cell', function () {
            expect(Game.getCell(0, 2)).toBeDefined();
        });

    });

    describe('when game step is happen', function () {

        beforeEach(function () {
            Game.init({ height: 4, width: 4});
        });

        describe('live cell with fewer than two live neighbours', function () {

            beforeEach(function () {
                Game.putCell(0, 0);
                Game.nextStep();
            });

            it ('should cell die', function () {
                expect(Game.getCell(0, 0).state).toEqual(CellState.Dead);
            });

        });

        describe('live cell with fewer than two live neighbours', function () {

            beforeEach(function () {
                Game.putCell(0, 0);
                Game.putCell(0, 1);
                Game.nextStep();
            });

            it ('should cell die', function () {
                expect(Game.getCell(0, 0).state).toEqual(CellState.Dead);
            });

        });

        describe('live cell with two or three live neighbours lives on to the next generation', function () {

            beforeEach(function () {
                Game.putCell(0, 0);
                Game.putCell(0, 1);
                Game.putCell(1, 0);
                Game.nextStep();
            });

            it ('should cell live', function () {
                expect(Game.getCell(0, 0).state).toEqual(CellState.Live);
            });

            it ('rest cells should be dead', function () {
                expect(Game.getCell(0, 1).state).toEqual(CellState.Dead);
                expect(Game.getCell(1, 0).state).toEqual(CellState.Dead);
            });

        });

        describe('live cell with more than three live neighbours dies, as if by overcrowding', function () {

            beforeEach(function () {
                Game.putCell(0, 0);
                Game.putCell(0, 1);
                Game.putCell(1, 0);
                Game.putCell(1, 1);
                Game.nextStep();
            });

            it ('should die', function () {
                expect(Game.getCell(0, 0).state).toEqual(CellState.Dead);
            });
        });

        describe('dead cell with exactly three live neighbours becomes a live cell, as if by reproduction', function () {

            beforeEach(function () {
                Game.putCell(0, 0, CellState.Dead);
                Game.putCell(0, 1);
                Game.putCell(1, 0);
                Game.putCell(1, 1);
                Game.nextStep();
            });

            it ('should live', function () {
                expect(Game.getCell(0, 0).state).toEqual(CellState.Live);
            });

        });

    });

});

game.spec2.js

    describe('when game step is happen 2x2 grid', function () {

        beforeEach(function () {
            Game.init({ height: 2, width: 2});
        });

        describe('live cell with fewer than two live neighbours', function () {

            beforeEach(function () {
                Game.putCell(0, 0);
                Game.nextStep();
            });

            it ('should cell die', function () {
                expect(Game.getCell(0, 0).state).toEqual(CellState.Dead);
            });

        });

        describe('live cell with fewer than two live neighbours', function () {

            beforeEach(function () {
                Game.putCell(0, 0);
                Game.putCell(0, 1);
                Game.nextStep();
            });

            it ('should cell die', function () {
                expect(Game.getCell(0, 0).state).toEqual(CellState.Dead);
            });

        });

        describe('live cell with two or three live neighbours lives on to the next generation', function () {

            beforeEach(function () {
                Game.putCell(0, 0);
                Game.putCell(0, 1);
                Game.putCell(1, 0);
                Game.nextStep();
            });

            it ('should cell live', function () {
                expect(Game.getCell(0, 0).state).toEqual(CellState.Live);
            });

            it ('rest cells should be dead', function () {
                expect(Game.getCell(0, 1).state).toEqual(CellState.Dead);
                expect(Game.getCell(1, 0).state).toEqual(CellState.Dead);
            });

        });

        describe('live cell with more than three live neighbours dies, as if by overcrowding', function () {

            beforeEach(function () {
                Game.putCell(0, 0);
                Game.putCell(0, 1);
                Game.putCell(1, 0);
                Game.putCell(1, 1);
                Game.nextStep();
            });

            it ('should die', function () {
                expect(Game.getCell(0, 0).state).toEqual(CellState.Dead);
            });
        });

        describe('dead cell with exactly three live neighbours becomes a live cell, as if by reproduction', function () {

            beforeEach(function () {
                Game.putCell(0, 0, CellState.Dead);
                Game.putCell(0, 1);
                Game.putCell(1, 0);
                Game.putCell(1, 1);
                Game.nextStep();
            });

            it ('should live', function () {
                expect(Game.getCell(0, 0).state).toEqual(CellState.Live);
            });

        });

    });