#include<iostream>
#include<queue>
#include<algorithm>
#include<list>
#include<map>
#include<vector>
#include<string>
#include<cstring>
#include<cstdlib>
#include<cstdio>
using namespace std;
#define Author "DemoVersion"
#define MAXN -
#define ull unsigned long long
const int inf (3<<30);
char chmap[255];
bool isadd[255];
void en(string &str){
    for(int i=0;i<str.length();i++)
        str[i]=chmap[str[i]];
}
int main()
{
    map<string,bool> m;
    int i,T,N;

    string text,key,tmp,ftmp,finals;
    cin>>T;
    while(T--){
        m.clear();
        cin>>N>>text>>key;
        for(i=0;i<255;i++)isadd[i]=false;
        for(i=0;i<26;i++)chmap['a'+i]=key[i];
        tmp="";
        for(i=0;i<text.length();i++){
            if(isadd[text[i]]==0){
                isadd[text[i]]=1;
                tmp+=text[i];
            }
        }
        ftmp=tmp;
        m[tmp]=true;
        while(1){
            en(tmp);
            if(m.count(tmp)>0)break;
            m[tmp]=true;
        }
        finals=m.begin()->first;
        for(int i=0;i<ftmp.length();i++)
			chmap[ftmp[i]]=finals[i];
        for(i=0;i<text.length();i++)
			text[i]=chmap[text[i]];
        cout<<text<<endl;
    }
    return 0;
}