#include <bits/stdc++.h>

using namespace std;

int main() {
    int time;
    scanf("%d", &time);
    while (time--) {
        int m, n;
        scanf("%d%d\n", &m, &n);
        char dna[m][n + 2];
        char out[n];
        int i, j;
        for (i = 0; i < m; i++)
            scanf("%s", dna[i]);
        int sum = 0;
        for (j = 0; j < n; j++) {
            int A = 0, C = 0, G = 0, T = 0, max = 0;
            for (i = 0; i < m; i++) {
                if (!(dna[i][j] - 'A'))
                    A++;
                else if (!(dna[i][j] - 'G'))
                    G++;
                else if (!(dna[i][j] - 'C'))
                    C++;
                else if (!(dna[i][j] - 'T'))
                    T++;
            }
            if (max < A)
                max = A;
            if (max < C)
                max = C;
            if (max < G)
                max = G;
            if (max < T)
                max = T;
            if (max == A)
                out[j] = 'A';
            else if (max == C)
                out[j] = 'C';
            else if (max == G)
                out[j] = 'G';
            else if (max == T)
                out[j] = 'T';
            printf("%c", out[j]);
            sum += max;
        }
        printf("\n%d\n", m * n - sum);
    }
    return 0;
}