#include <cstdio>
#include <iostream>
#include <string>
#include <cstring>
#define LL long long
#define lowbit(x) ((x) & (-x))
const int MAXN = 1e3 + 5;
const int INF = 0x3f3f3f3f;
using namespace std;
 
struct SCAN
{
    char c;
    int num;
}scan;
 
char str[55][MAXN];
int num[30];
 
int main()
{
    //freopen("input.txt", "r", stdin);
    int n, i, j, T, leng;
    scanf("%d", &T);
    while (T--)
    {
        int nerr = 0;
        scanf("%d%d%*c", &n, &leng);
        string ans;
        for (i = 0; i < n; i++)
            scanf("%s", str[i]);
        for (i = 0; i < leng; i++)
        {
            memset(num, 0, sizeof num);
            for (j = 0; j < n; j++)
                num[str[j][i] - 'A']++;
            scan.c = 'A', scan.num = num[0];
            for (j = 1; j < 30; j++)
                if (num[j] > scan.num)
                    scan.c = j + 'A', scan.num = num[j];
            ans += scan.c;
            for (j = 0; j < 30; j++)
                if (j + 'A' != scan.c)
                    nerr += num[j];
        }
        cout << ans << endl;
        cout << nerr << endl;
    }
    return 0;
}