#include<bits/stdc++.h>
using namespace std;
const int N=5e5+10;
struct Point
{
    double x,y;
    Point(){}
    Point(double a,double b):x(a),y(b){}
    void input(){scanf("%lf%lf",&x,&y);} 
    friend bool operator<(Point a,Point b){return a.x!=b.x?a.x<b.x:a.y<b.y;}
    friend bool operator==(Point a,Point b){return a.x==b.x && a.y==b.y;}
    friend Point operator-(Point a,Point b){ return {a.x-b.x,a.y-b.y};}
    friend double det(Point a,Point b){return a.x*b.y-a.y*b.x;}
    friend double dis(Point a,Point b){Point p=a-b;return sqrt(p.x*p.x+p.y*p.y);}
};
Point P[N],sta[N];int n,top;

void Andrew()
{
    sort(P+1,P+n+1);
    top=0;
    for(int i=1;i<=n;i++)
    {
        while( top>1 && det(sta[top]-sta[top-1],P[i]-sta[top-1])<=0 ) top--;
        sta[++top]=P[i];
    }
    int t=top;
    for(int i=n-1;i>=1;i--)
    {
        while( top>t && det(sta[top]-sta[top-1],P[i]-sta[top-1])<=0 ) top--;
        sta[++top]=P[i];
    }
    n=top-1;//注意：sta[1]和sta[top]都是P[1]  
    while(n>1 && sta[n]==sta[n-1]) n--;
}
int main()
{
    int T;scanf("%d",&T);
    while(T--)
    {
        scanf("%d",&n);
        for(int i=1;i<=n;i++)P[i].input();
        if(n==0) {printf("0\n");continue;}
        if(n==1) {printf("1\n%0.0lf %0.0lf\n",P[1].x,P[1].y);continue;} 
        Andrew();
        printf("%d\n",n);  
        for(int i=1;i<=n;i++) printf("%0.0lf %0.0lf\n",sta[i].x,sta[i].y);
    }
    return 0;
}