#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int Mod=1e9+7;
const ll INF = 10000000000000;
const int N = 1e6+7;
 
    void solve() {
        int n;
        cin >> n;
        vector<pair<int,int>> a(n);
        for(int i=0;i<n;i++) cin >> a[i].first >> a[i].second;
        sort(a.begin(),a.end());
        for(int i=0;i<n;i++) cout << a[i].first << " " << a[i].second << " ";
        cout << '\n';
      }       
 
int main(){ 
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
 
    int t;
    cin >> t;
    while (t--) solve();
 
    return 0;
}
 

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