#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef pair<ll,ll> P;
#define REP(i,n) for(ll i=0;i<ll(n);i++)









int main(void){
	cin.tie(nullptr);  ios_base::sync_with_stdio(false);
	ll i,j;





	int T;
	cin >> T;
	while(T--){


		ll K;
		string S;
		cin >> K >> S;


		ll n=S.size();

		if(K>=n-1){

			REP(i,n) cout << S[0];
			cout << endl;

		}else{

			string s;
			REP(i,K) s+=S[0];

			s+=S;

			ll m=s.size();
			s.erase(m-K);


			cout << s << endl;

		}










	}









	return 0;

}