#include <bits/stdc++.h>
using namespace std;

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    int T; cin >> T;
    while(T--){
        int K; cin >> K;
        string s; cin >> s;
        K = min(K,(int)s.size());
        reverse(s.begin(),s.end());
        s += string(K,s.back());
        reverse(s.begin(),s.end());
        while(K--) s.pop_back();
        cout << s << "\n";
    }
}