import std.conv, std.functional, std.range, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.bitmanip, std.complex, std.container, std.math, std.mathspecial, std.numeric, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }

string COLOR(string s = "") { return "\x1b[" ~ s ~ "m"; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }




void main() {
  try {
    for (; ; ) {
      const numCases = readInt;
      foreach (caseId; 0 .. numCases) {
        const N = readInt;
        const S = readToken;
        
        auto cs = S.dup;
        if (N == 1) {
          cs[0] = 'B';
        } else {
          if (S[0] == 'A') {
            if (S[1] == 'A') {
              cs[0] = cs[1] = 'B';
            } else {
              cs[0] = cs[1] = 'B';
              foreach (i; 2 .. N) if (S[i] == 'B') {
                foreach (j; i .. N) {
                  if (S[j] == 'B') {
                    cs[j] = 'A';
                  } else {
                    break;
                  }
                }
                break;
              }
            }
          } else {
            if (S[1] == 'A') {
              cs[0] = cs[1] = 'B';
              foreach (i; 2 .. N) {
                if (S[i] == 'B') {
                  cs[i] = 'A';
                } else {
                  break;
                }
              }
            } else {
              cs[0] = cs[1] = 'B';
            }
          }
        }
        writeln(cs);
      }
    }
  } catch (EOFException e) {
  }
}