#include <bits/stdc++.h>
using namespace std;
using ll = long long;

void solve(){
    int n;
    string s;
    cin >> n >> s;
    if(n == 1){
        cout << "A\n";
        return;
    }
    int p0 = 0, p1 = 1;
    for(int i = 0; i < 3 * n; i++){
        if(i % 2 == 0){
            if(p0 >= n) break;
            if(p1 < p0 && s[p1] <= 'B') break;
            if(s[p0] <= 'B') break;
            s[p0] = 'A';
            p0 += 2;
        }else{
            if(p1 >= n) break;
            if(s[p1] == 'C') break;
            s[p1]++;
            if(s[p1] == 'C') p1 += 2;
        }
    }
    cout << s << '\n';
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int T;
    cin >> T;
    while(T--) solve();
}