using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    static int[][] NArr(long n) => Enumerable.Repeat(0, (int)n).Select(_ => NList).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var t = NN;
        var ans = new List<string>();
        for (var u = 0; u < t; ++u)
        {
            var c = NList;
            var (n, l) = (c[0], c[1]);
            var map = NArr(n);
            ans.AddRange(Drone(n, l, map));
        }
        WriteLine(string.Join("\n", ans));
    }
    static List<string> Drone(int n, int l, int[][] map)
    {
        var div = (int)Math.Sqrt(n);
        var width = (l + div) / div;
        var list = new List<int[]>[div];
        for (var i = 0; i < list.Length; ++i) list[i] = new List<int[]>();
        for (var i = 0; i < n; ++i)
        {
            list[map[i][1] / width].Add(map[i]);
        }
        for (var i = 0; i < list.Length; ++i)
        {
            if (i % 2 == 0) list[i].Sort((l, r) => l[0].CompareTo(r[0]));
            else list[i].Sort((l, r) => r[0].CompareTo(l[0]));
        }
        var ans = new List<string>{ n.ToString() };
        foreach (var li in list) foreach (var m in li) ans.Add($"{m[0]} {m[1]}");
        return ans;
    }
}