#include<iostream>
#include<cassert>
using namespace std;
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int T;cin>>T;
	for(;T--;)
	{
		int N;
		string S;
		cin>>N>>S;
		const char flip='A'^'B';
		if(N<=2);
		else
		{
			if(S[0]=='A')
			{
				if(S[1]=='A')
				{
					S[1]^=flip;
					for(int j=2;j<N&&S[j]=='B';j++)S[j]^=flip;
				}
				else
				{
					int j=2;
					while(j<N&&S[j]=='A')j++;
					for(;j<N&&S[j]=='B';j++)S[j]^=flip;
				}
			}
			else
			{
				if(S[1]=='B')S[0]^=flip;
				else
				{
					S[0]^=flip;
					S[1]^=flip;
					for(int j=2;j<N&&S[j]=='B';j++)S[j]^=flip;
				}
			}
		}
		int i=0;
		while(i<N&&S[i]=='B')i++;
		for(;i<N&&S[i]=='A';i++)S[i]^=flip;
		cout<<S<<"\n";
	}
}