I=input
for t in range(int(I())):
	N,S,i,f=int(I()),[c for c in I()],0,1
	while i<N:
		if f:
			if S[i]>'B':S[i],i='A',i+1
			else:i=N
		elif S[i]<'B':S[i]='B';i=N
		elif S[i]<'C':S[i],i='C',i+1
		else:i=N
		f^=1
	print(*S,sep='')