for _ in range(int(input())):
    N = int(input())
    S = input()
    if N == 1:
        print("B")
    elif N == 2:
        print("BB")
    elif S.startswith("AA"):
        l = list(S)
        l[0] = l[1] = "B"
        for i in range(2, N):
            if l[i] == "B":
                l[i] = "A"
            else:
                break
        print("".join(l))
    elif S.startswith("AB"):
        l = list(S)
        l[0] = l[1] = "B"
        t = False
        for i in range(2, N):
            if l[i] == "B":
                l[i] = "A"
                t = True
            elif t:
                break
        print("".join(l))
    elif S.startswith("BA"):
        l = list(S)
        l[0] = l[1] = "B"
        for i in range(2, N):
            if l[i] == "B":
                l[i] = "A"
            else:
                break
        print("".join(l))
    elif S.startswith("BB"):
        l = list(S)
        print("".join(l))