app.js

var single_pair_validator = function(hand){
  
};

var high_card_validation = function(white_numbered_hand, black_numbered_hand){
  for(var i=0; i < white_numbered_hand.length; i++){
    if(white_numbered_hand[i] > black_numbered_hand[i]){
      return "White wins";
    }
    if(white_numbered_hand[i] < black_numbered_hand[i]){
      return "Black wins";
    }
  }
  return "They tie";
};

var poker_validator = function(white_hand, black_hand) {
  var white_numbered_hand = convert_hand_to_numbers(white_hand);
  white_numbered_hand = white_numbered_hand.sort(sortNumber);
  var black_numbered_hand = convert_hand_to_numbers(black_hand);
  black_numbered_hand = black_numbered_hand.sort(sortNumber);
  
  var validators = [high_card_validation];
  var result;
  for(var i = 0; i < validators.length; i++){
    result = validators[i](white_numbered_hand, black_numbered_hand);
  }
  return result;
};

var convert_card_to_number = function(card){
  var rank = card.slice(0, card.length - 1);
  var suit = card.slice(-1);
  var number = parseInt(rank);
  
  if(!isNaN(number)){
    return number;
  }
  return {
     "J": 11,
     "Q": 12,
     "K": 13, 
     "A": 14 
  }[rank];
};

var convert_hand_to_numbers = function(hand){
  var result = Array();
  for(var i=0; i < hand.length; i++){
    result.push(convert_card_to_number(hand[i]));
  }
  return result;
}

var highest_card = function(hand){
    var numbered_hand = convert_hand_to_numbers(hand);
    return numbered_hand.sort(sortNumber)[0];
};

function sortNumber(a,b) {
    return b - a;
}

test.js

describe('Highest Card Finder',function(){
  it('finds highest number', function(){
    var hand = ['2H', '3D', '5S', '9C', '4H'];
    expect(highest_card(hand)).toBe(9);
  });
  it('finds king', function(){
    var hand = ['2H', '3D', '5S', '9C', 'KH'];
    expect(highest_card(hand)).toBe(13);
  });
  it('finds queen', function(){
    var hand = ['2H', '3D', '5S', '9C', 'QH'];
    expect(highest_card(hand)).toBe(12);
  });
});

describe('Convert Card To Number',function(){
  it('converts number', function(){
    expect(convert_card_to_number("4H")).toBe(4);
  });
  it('converts non number', function(){
    expect(convert_card_to_number("JH")).toBe(11);
  });
  it('converts 10', function(){
    expect(convert_card_to_number("10H")).toBe(10);
  });
});

describe('Convert Hand To Numbers',function(){
  it('converts number', function(){
    var hand = ["4H", "3C", "KD", "AS", "8S"];
    var result = [4,3,13,14,8];
    expect(convert_hand_to_numbers(hand)).toEqual(result);
  });
  it('converts non number', function(){
    expect(convert_card_to_number("JH")).toBe(11);
  });
});

describe('Poker Validator',function(){
  it('says black wins',function(){
    var white_hand = ['2H', '3D', '5S', '9C', 'KD'];
    var black_hand = ['2C', '3H', '4S', '8C', 'AH'];
    expect(poker_validator(white_hand, black_hand)).toBe('Black wins');
  });

  it('says white wins',function(){
    var black_hand = ['2H', '3D', '5S', '9C', 'KD'];
    var white_hand = ['2C', '3H', '4S', '8C', 'AH'];
    expect(poker_validator(white_hand, black_hand)).toBe('White wins');
  });

  it('says they tie with same cards',function(){
    var black_hand = ['2H', '3D', '5S', '9C', 'KD'];
    var white_hand = ['2C', '3H', '5C', '9H', 'KH'];
    expect(poker_validator(white_hand, black_hand)).toBe('They tie');
  });

  it('says black wins with matching highest card',function(){
    var black_hand = ['2H', '3D', '5S', '9C', 'KD'];
    var white_hand = ['2C', '3H', '4S', '8C', 'KH'];
    expect(poker_validator(white_hand, black_hand)).toBe('Black wins');
  });

  it('says white wins with matching highest card with reversed ordering',function(){
    var black_hand = ['KD', '2H', '3D', '7C', '5S'];
    var white_hand = ['2C', 'KH', '3H', '4S', '8C'];
    expect(poker_validator(white_hand, black_hand)).toBe('White wins');
  });
});

describe('Pair Validator',function(){
  it('hand has pair',function(){
    var hand = ['2H', '2D', '5S', '9C', 'KD'];
    expect(pair_validator(hand)).toBeTruthy();
  });
});