#include<bits/stdc++.h>
using namespace std;
#define pii pair<int,int>
#define ff first
#define ss second
#define mp make_pair
#define pb push_back
#define N 505
#define ll long long 
#define mod 1000000007
map<int,int> mark1,mark2;
int main() {
    int q;
    cin>>q;
    while(q--)
    {
    	int n,a,b,cnt1=0,cnt2=0,i;
    	cin>>n;
    	mark1.clear();
           mark2.clear();
        for(i=1;i<=n;i++)
    	{
    	  cin>>a>>b;
    	  if(mark1[a]==0)
    	    cnt1++;
    	  if(mark2[b]==0)
    	    cnt2++;
    	  mark1[a]++;
    	  mark2[b]++;
    	}
    	if(cnt1==2&&cnt2==2)
    	  cout<<"YES\n";
    	else
    	  cout<<"NO\n";
    }
    return 0;
}