import std;

void main(){
	auto T = readln.chomp.to!int;
	for(auto t = 0; t < T; t++){
		auto N = readln.chomp.to!int;
		auto S = readln.chomp;
		auto s = "";
		auto b = 0;
		for(auto i = N - 1; i >= 0; i--){
			if(S[i] == 'B'){
				b++;
				continue;
			}
			if(b == 0){
				s ~= "A";
				continue;
			}
			b--;
			if(b == 0 && (s.length == 0 || s[$ - 1] == 'A')){
				s ~= "BA";
			}
		}
		if(b > 0){
			s ~= "B".cycle.take(b).to!string;
		}
		writeln(s.retro);
	}
}