#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
//const int INF = 1e9;
//const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n) - 1; i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r) - 1;i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }

int main() {
	std::ios::sync_with_stdio(false);
	std::cin.tie(nullptr);
	int t; cin >> t;
	while (t--) {
		int n; cin >> n;
		string s; cin >> s;
		if (n == 1) {
			if (s == "A")s = "B";
			else s = "A";
			cout << s << endl;
			continue;
		}
		if (n == 2) {
			if (s == "BB") cout << "BB" << endl;
			else cout << "BA" << endl;
			continue;
		}
		if (s == "AB") {
			cout << "BA" << endl;
			continue;
		}
		// AB.....
		if (s[0] == 'A' && s[1] == 'B') {
			int idx = -1;
			rep2(i, 2, n) {
				if (s[i] == 'A')continue;
				idx = i;
				while (i < n&&s[i] == 'B') {
					s[i] = 'A';
					i++;
				}
				break;
			}
			if (idx = -1)s.back() = 'B';
		}
		// BA.....
		else if (s[0] == 'A' && s[1] == 'B') {
			s[1] = 'A';
			s[1] = 'B';
			rep2(i, 2, s.size()) {
				if (s[i] == 'A')break;
				s[i] = 'A';
			}
		}
		// AA.....
		else if (s[0] == 'A' && s[1] == 'A') {
			s[1] = 'B';
			rep2(i, 2, s.size()) {
				if (s[i] == 'A')break;
				s[i] = 'A';
			}
		}
		// BB.....
		else if (s[0] == 'B' && s[1] == 'B') {
			s[0] = 'A';
		}
		// AB.........
		// BB.........

		s[0] = 'B';
		s[1] = 'B';
		cout << s << endl;
	}
	return 0;
}