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

int main() {
    int k = 0;
    cin>>k;
    while(k--){
        int n = 0;
        cin>>n;
        vector<pair<int, int>> v(n);
        for(int i = 0; i<n; i++){
            cin>>v[i].first>>v[i].second;
        }
        if(n<=3){
            cout<<"YES"<<endl;
            continue;
        }
        vector<int> x;
        for(int i = 0; i < v.size(); i++){
            if(find(x.begin(), x.end(), v[i].first) != x.end()){
                v.erase(v.begin() + i);
                i--;
            }
            else{
                x.push_back(v[i].first);
            }
        }
        vector<int> y;
        for(int i = 0; i < v.size(); i++){
            if(find(y.begin(), y.end(), v[i].second) != y.end()){
                v.erase(v.begin() + i);
                i--;
            }
            else{
                y.push_back(v[i].second);
            }
        }
        if(v.size() == 0)
            cout<<"YES"<<endl;
        else
            cout<<"NO"<<endl;
        
    }
    return 0;
}