#include<iostream>
#include <vector>
#include <bitset>
#include <string>
#include <queue>
#include <set>
#include <algorithm>

using namespace std;



auto main()->int
{
   long long q;
   cin>>q;
   while(q--)
   {
        long long a;
        cin>>a;
        set<long long>s;
        for(auto i=0;i<a;i++)
        {
            long long x, y;
            cin>>x>>y;
            s.insert(x);
            s.insert(y);
        }
        if(s.size()>2)
        {
            cout<<"NO"<<endl;
        }
        else{
            cout<<"YES"<<endl;
        }
   }
}