#include <iostream>

#include <cstdio>

#include <cstring>

#include <cmath>

#include <algorithm>

using namespace std;

const int N = 55;

int num[N];

char s[N];

void solve()

{

	int n , m;

	cin >> n >> m;

	memset(s,0,sizeof(s));

	for(int i = 1;i <= n;i ++)

		cin >> num[i];

	for(int i = 1;i <= m;i ++)

		s[i] = 'B';

	for(int i = 1;i <= n;i ++)

	{

		int a = num[i];

		int b = m + 1 - num[i];

		if(a < b && s[a] != 'A')

			s[a] = 'A';

		else if(a > b && s[b] == 'A')

			s[a] = 'A';

		else

			s[b] = 'A';

	}

	for(int i = 1;i <= m;i ++)

		cout << s[i];

	cout << endl;

}

int main()

{

	int T;

	cin >> T;

	while(T --)

		solve();

	return 0;

}