#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
using ll = long long;
constexpr int INF = 0x3f3f3f3f;
constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr double EPS = 1e-8;
constexpr int MOD = 998244353;
// constexpr int MOD = 1000000007;
constexpr int DY4[]{1, 0, -1, 0}, DX4[]{0, -1, 0, 1};
constexpr int DY8[]{1, 1, 0, -1, -1, -1, 0, 1};
constexpr int DX8[]{0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U>
inline bool chmax(T& a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U>
inline bool chmin(T& a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << fixed << setprecision(20);
  }
} iosetup;

template <typename T>
requires requires { typename T::value_type; }
std::vector<std::pair<typename T::value_type, int>> run_length_encoding(
    const T& s) {
  const int n = s.size();
  std::vector<std::pair<typename T::value_type, int>> res;
  if (n == 0) [[unlikely]] return res;
  typename T::value_type ch = s.front();
  int num = 1;
  for (int i = 1; i < n; ++i) {
    if (s[i] != ch) {
      res.emplace_back(ch, num);
      num = 0;
    }
    ch = s[i];
    ++num;
  }
  res.emplace_back(ch, num);
  return res;
}

int main() {
  int t; cin >> t;
  while (t--) {
    int n; string s; cin >> n >> s;
    const auto rle = run_length_encoding(s);
    if (s.front() == 'A') {
      s[0] = 'B';
      if (rle.front().second >= 3) {
        s[1] = 'B';
      } else if (rle.front().second == 2) {
        s[1] = 'B';
        if (rle.size() >= 2) {
          REP(i, rle[1].second) s[i + 2] = 'A';
        }
      } else {
        if (rle.size() >= 2 && rle[1].second >= 2) {
          const int fr = rle[0].second;
          FOR(i, fr + 1, fr + rle[1].second) s[i] = 'A';
        } else if (rle.size() >= 4) {
          const int fr = rle[0].second + rle[1].second + rle[2].second;
          FOR(i, fr, fr + rle[3].second) s[i] = 'A';
        }
      }
    } else if (s.front() == 'B') {
      if (rle.front().second == 1 && rle.size() >= 2) {
        s[1] = 'B';
        if (rle[1].second >= 3) {
          s[2] = 'B';
        } else if (rle[1].second == 2) {
          s[2] = 'B';
          if (rle.size() >= 2) {
            REP(i, rle[1].second) s[i + 2] = 'A';
          }
        } else {
          if (rle.size() >= 3 && rle[2].second >= 2) {
            const int fr = rle[0].second + rle[1].second;
            FOR(i, fr + 1, fr + rle[2].second) s[i] = 'A';
          } else if (rle.size() >= 5) {
            const int fr = rle[0].second + rle[1].second + rle[2].second + rle[3].second;
            FOR(i, fr, fr + rle[4].second) s[i] = 'A';
          }
        }
      }
    }
    cout << s << '\n';
  }
  return 0;
}