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


int main() {
    int q, n;
	int a, b;
	cin >> q;

	for (int i = 0; i < q; ++i) {
		set<int> sx, sy;
		bool yes = true;
        
        cin >> n;				
		
        cin >> a>> b;
        sx.insert(a);
        sy.insert(b);
        
		for (int j = 1; j < n; ++j) {						
			cin >> a >> b;		
			
            if (sx.find(a) == sx.end() && sy.find(b) == sy.end())
			{
				yes = false;
				break;
			}
            
            sx.insert(a);
            sy.insert(b);
		}

		cout << (yes ? "YES" : "NO") << endl;
    }
    return 0;
}