#include<iostream>

 #include<algorithm>

 #include<cstdio>

 #include<cstring>

 #include<vector>

 using namespace std;

 struct T

 {

     int x,y;

     friend int operator < (T a, T b)

 {

     if((a.x<b.x) || (a.x==b.x && a.y<b.y))

         return ;

     return ;

 }

 }a[],ans[];

 //用来判断第三点在当前两点构成的直线的左侧还是右侧，右侧返回值小于0；

 double judge(T a, T b,T c)

 {

   return (b.x-a.x)*(c.y-a.y)-(c.x-a.x)*(b.y-a.y);

 }

 int main()

 {

   int T,m;

   scanf("%d",&T);

   while(T--)

   {

       scanf("%d",&m);

       for(int i=; i<m; i++)

       {

         scanf("%d %d",&a[i].x,&a[i].y);

       }

    sort(a,a+m);

    int k1=;

    for(int i=; i<m; i++)//下凸包，从下面扫描个点；

    {

        while(k1> && judge(ans[k1-],ans[k1-],a[i])<=)

        {

             k1--;

        }

      ans[k1++]=a[i];

    }

     int k2=k1;

     for(int i=m-; i>=; i--)//上凸包，从上面扫描各点；

    {

        while(k1>k2 && judge(ans[k1-],ans[k1-],a[i])<=)

        {

             k1--;

        }

      ans[k1++]=a[i];

    }

    k1--;

    sort(ans,ans+k1);

    for(int i=; i<k1; i++)

     printf("%d %d\n",ans[i].x,ans[i].y);

   }

   return ;

 }