#include <bits/stdc++.h>
using namespace std;
#define int long long int
#define endl "\n" 

signed main(){
    ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    int t;cin>>t;
    while(t--){
        int k;cin>>k;
        string s;cin>>s;
        int n = s.size();
        string ans;
        if(k>=n){
            string t(n,s[0]);
            ans = t;
        }else{
            ans = s.substr(0,n-k);
            string t(k,s[0]);
            ans = t+ans;
        }
        cout<<ans<<endl;
    }
    return 0;
}