namespace AtCoder;

#nullable enable

using System.Numerics;

static class Extensions
{
    public static T[] Repeat<T>(this int time, Func<T> F) => Enumerable.Range(0, time).Select(_ => F()).ToArray();
}

class AtCoder
{
    object? Solve()
    {
        var t = Int();
        var ans = new List<List<(int, int)>>();
        for (var i = 0; i < t; i++)
        {
            ans.Add(Solve2());
        }
        foreach (var l in ans)
        {
            Out(l.Count);
            foreach (var (x, y) in l) Out(x + " " + y);
        }
        return null;
    }

    List<(int, int)> Solve2()
    {
        var res = new List<(int, int)>();
        var n = Int();
        var l = Int();
        var d = 1;
        while (d * d <= n * 2) d++;
        var z = l / d + 1;
        var g = new Dictionary<(int, int), List<(int, int)>>();
        for (var i = 0; i < n; i++)
        {
            var x = Int();
            var y = Int();
            var (xd, yd) = (x / z, y / z);
            if (!g.ContainsKey((xd, yd))) g[(xd, yd)] = new();
            g[(xd, yd)].Add((x, y));
        }
        var kz = new List<(int, int)>(g.Keys);
        kz.Sort();
        var kz2 = new Dictionary<int, List<int>>();
        foreach (var (x, y) in kz)
        {
            if (!kz2.ContainsKey(x)) kz2[x] = new();
            kz2[x].Add(y);
        }
        var rev = false;
        foreach (var (x, yl) in kz2)
        {
            yl.Sort();
            if (rev)
            {
                yl.Reverse();
                rev = !rev;
            }
            foreach (var y in yl)
            {
                var a = g[(x, y)];
                a.Sort();
                foreach (var (xo, yo) in a) res.Add((xo, yo));
            }
        }

        {
            var check = 0L;
            var (xl, yl) = res[^1];
            foreach (var (x, y) in res)
            {
                check += Math.Abs(x - xl) + Math.Abs(y - yl);
                (xl, yl) = (x, y);
            }
            if (check >= 1000L * l) throw new Exception();
        }

        return res;
    }

    public static void Main() => new AtCoder().Run();
    public void Run()
    {
        var res = Solve();
        if (res != null)
        {
            if (res is bool yes) res = yes ? "Yes" : "No";
            sw.WriteLine(res);
        }
        sw.Flush();
    }

    string[] input = Array.Empty<string>();
    int iter = 0;
    readonly StreamWriter sw = new(Console.OpenStandardOutput()) { AutoFlush = false };

    #pragma warning disable IDE0051
    string String()
    {
        while (iter >= input.Length) (input, iter) = (Console.ReadLine()!.Split(' '), 0);
        return input[iter++];
    }
    T Input<T>() where T : IParsable<T> => T.Parse(String(), null);
    int Int() => Input<int>();
    void Out(object? x, string? separator = null)
    {
        separator ??= Environment.NewLine;
        if (x is System.Collections.IEnumerable obj and not string)
        {
            var firstLine = true;
            foreach (var item in obj)
            {
                if (!firstLine) sw.Write(separator);
                firstLine = false;
                sw.Write(item);
            }
        }
        else sw.Write(x);
        sw.WriteLine();
    }
    #pragma warning restore IDE0051
}