Kumite

function groupCombinations_() {
    var r = [], arg = arguments, max = arg.length-1;
    function helper(arr, i) {
        for (var j=0, l=arg[i].length; j<l; j++) {
            var a = arr.slice(0); 
            a.push(arg[i][j]);
            if (i==max)
                r.push(a);
            else
                helper(a, i+1);
        }
    }
    helper([], 0);
    return r;
}

function groupCombinationsCheck(arr2D) {
    var combL = groupCombinations_.apply(this, arr2D);
    return [combL.length, combL];
}



describe("Basic Tests", function(){
  it("Simple Cases", function(){
    var arr2D = [[1,2,3,4], [1,2,3,4,5,6]];
    Test.assertSimilar(groupCombinations(arr2D), [24, [[1, 1], [1, 2], [1, 3], [1, 4],
    [1, 5], [1, 6], [2, 1], [2, 2],[2, 3], [2, 4], [2, 5], [2, 6], [3, 1], [3, 2], 
    [3, 3], [3, 4], [3, 5], [3, 6], [4, 1], [4, 2], [4, 3], [4, 4],[4, 5], [4, 6]]]);
    
    arr2D = [[1,2,3,4,5,6], [1,2,3,4,5,6]]; 
    Test.assertSimilar(groupCombinations(arr2D), [36, [[1, 1], [1, 2], [1, 3], [1, 4],
    [1, 5], [1, 6], [2, 1], [2, 2], [2, 3], [2, 4], [2, 5], [2, 6], [3, 1], [3, 2], 
    [3, 3], [3, 4], [3, 5], [3, 6], [4, 1], [4, 2], [4, 3], [4, 4], [4, 5], [4, 6], 
    [5, 1], [5, 2], [5, 3], [5, 4], [5, 5], [5, 6], [6, 1], [6, 2], [6, 3], [6, 4],
    [6, 5], [6, 6]]]);
  });
});

function range(start, stop){
    var a=[start], b=start;
    while(b<stop){b++;a.push(b)}
    return a;
}

function randint(min, max) {
    return Math.floor(Math.random() * (max - min + 1)) + min;
}

function choice(items) {
    var item = items[Math.floor(Math.random()*items.length)];
    return item;
}

describe("Random Tests", function(){
  it("Challenging Cases", function(){
    var ranges = [range(1, 4), range(1,6), range(1,8), range(1,10), range(1,12), range(1,20)];
    for (var h = 1; h <= 20 ; h ++) {
        var n = randint(2, 3);
        var arr2D = [];
        while (true){
            arr2D.push(choice(ranges))
            if (arr2D.length == n) break;
        }
        var result = groupCombinationsCheck(arr2D);
        var res = groupCombinations(arr2D);
        it("Testing for arr2D = " + arr2D.toString(), function(){
          Test.assertSimilar(res, result);
        })
    }
  })
})