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

void run(){
    int n;
    cin>>n;
    int x[n],y[n];
    bool ans[n];
    for(int i=0;i<n;i++){
        cin>>x[i]>>y[i];
        ans[i]=false;
    }
    
    
    
    for(int i=0;i<n;i++){
        for(int j=0;j<n;j++){
            if(x[i]==y[j] && x[j]==y[i] && i!=j){
                ans[i]=true;
                break;
            }
        }
    }
    int ggwp=0;
	for(int i=0;i<n;i++)
        if(!ans[i]){
        	ggwp++;
        	if(ggwp==2){
        		cout<<"NO"<<endl;
        		return ;
        	}
        }
    
    cout<<"YES"<<endl;
}

int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
    int q;
    cin>>q;
    for(int i=0;i<q;i++)
        run();
    return 0;
}