/*

     Name:nyoj-78-圈水池

     Copyright:

     Author:

     Date: 2018/4/27 9:52:48

     Description:

     Graham求凸包

     zyj大佬的模板，改个输出就能用

 */

 #include <cstring>

 #include <iostream>

 #include <cstdio>

 #include <algorithm>

 using namespace std;

 struct point{

     double x, y;

 };

 bool mult(point sp, point ep, point op){ //叉积

     return (sp.x - op.x) * (ep.y - op.y) >= (ep.x - op.x) * (sp.y - op.y);

 }

 inline bool operator < (const point &l, const point &r){

      return l.y < r.y || (l.y == r.y && l.x < r.x);

 }

 int graham(int n, point pnt[], point res[]){

     int i, len, top = ;

     sort(pnt, pnt + n);//排序找最小的点

     if (n == ){

         return ;

     }

     res[] = pnt[];

     if (n == ){

         return ;

     }

     res[] = pnt[];

     if (n == ){

         return ;

     }

     res[] = pnt[];

     for (i = ; i < n; i++){

         while (top && mult(pnt[i], res[top], res[top - ])){

             top--;

         }

         res[++top] = pnt[i];

     }

     len = top;

     res[++top] = pnt[n - ];

     for (i = n - ; i >= ; i--){

         while (top != len && mult(pnt[i], res[top], res[top - ])){

             top--;

         }

         res[++top] = pnt[i];

     }

     return top;  // 返回凸包中点的个数

 }

 bool cmp(const point &l, const point &r){

      return l.x < r.x || (l.x == r.x && l.y < r.y);

 }

 int main()

 {

     int t;

     cin>>t;

     point pnt[], res[];

     while (t--)  {

         memset(res, , sizeof(res));

         memset(pnt, , sizeof(pnt));

         int m;

         cin>>m;

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

             cin>>pnt[i].x>>pnt[i].y;

         int ct = graham(m, pnt, res);

         sort(res, res + ct, cmp);

         for (int i=; i<ct; i++) {

             printf("%.0f %.0f\n", res[i].x, res[i].y);

         }

     }

     return ;

 }