#include <bits/stdc++.h>
using namespace std;
using ll=long long;
int main(){
    int ttt;
    cin>>ttt;
    while(ttt--){
        int n;
        cin>>n;
        string s;
        cin>>s;
        if(n<=2){
            for(int i=0;i<n;i++)cout<<"B";
            cout<<endl;
            continue;
        }
        deque<pair<char,int>> rle;
        for(int i=0;i<n;i++){
            int l=i;
            while(i<n&&s[i]==s[l])i++;
            rle.push_back(make_pair(s[l],i-l));
            i--;
        }
        if(rle[0].first=='A'){
            if(rle[0].second==1){
                if(rle[1].second==1){
                    if(rle.size()>=4){
                        rle[3].first='A';
                    }
                    rle[0].first='B';
                }else{
                    if(rle.size()>=3){
                        rle[2].second+=rle[1].second-1;
                        rle[1].second=1;
                    }else{
                        rle.push_back(make_pair('A',rle[1].second-1));
                        rle[1].second=1;
                    }
                    rle[0].first='B';
                }
            }else if(rle[0].second==2){
                rle[1].first='A';
                rle[0].first='B';
            }else{
                rle[0].second-=2;
                rle.push_front(make_pair('B',2));
            }
        }else{
            if(rle[0].second==1){
                if(rle[1].second==1){
                    rle[2].first='A';
                    rle[1].first='B';
                }else{
                    rle[0].second++;
                    rle[1].second--;
                }
            }
        }
                            
        for(auto [c,i]:rle){
            while(i--)cout<<c;
        }
        cout<<endl;
    }
        
	return 0;
}