#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;


int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */  
    int q,i,n,j,k,x[10000],y[10000],flag=0;
    cin>>q;
    for(i=0; i<q; i++)
        {
        flag=0;
        cin>>n;
        for(j=0; j<n; j++)
            {
            cin>>x[j]>>y[j];
        }
        for(j=0; j<n; j++)
            {
            for(k=0; k<n; k++)
                {
                if((x[k]==x[j])||(y[k]==y[j]))
                    {
                    break;
                }
                if((x[k]!=x[j])&&(y[k]!=y[j]))
                        {
                    //cout<<j<<" "<<k<<endl;
                        flag=1;
                        break;
                    }
                }
            
            if(flag==1)
                {
                break;
            }
        }
        if(flag==1)
            cout<<"NO"<<endl;
        else
            cout<<"YES"<<endl;
    }
    return 0;
}