#include <stdio.h>
#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
using mint = modint998244353;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000005
#define Inf64 1000000000000000001LL

int main(){
	
	int _t;
	cin>>_t;
	rep(_,_t){
		int K;
		cin>>K;
		string S;
		cin>>S;
		
		K = min(K, (int)S.size());
		string ans = string(K,S[0]) + S;
		ans = ans.substr(0, S.size());
		cout<<ans<<endl;
	}
	
}