int hamming_distance(unsigned x, unsigned y)

{

    int dist = ;

    unsigned  val = x ^ y;

    // Count the number of bits set

    while (val != )

    {

        // A bit is set, so increment the count and clear the bit

        dist++;

        val &= val - ;

    }

    // Return the number of differing bits

    return dist;

}

#define _CRT_SECURE_NO_WARNINGS

#include<cmath>

#include<iostream>

#include<stdio.h>

#include<algorithm>

#include<cstring>

#include<stack>

#include<vector>

#include<string.h>

#include<queue>

#include<string>

#include<set>

#include<map>

using namespace std;

typedef long long ll;

#define mod 1000000007

#define rep(i,t,n)  for(int i =(t);i<=(n);++i)

#define per(i,n,t)  for(int i =(n);i>=(t);--i)

#define mmm(a,b) memset(a,b,sizeof(a))

#define eps 1e-6

#define pb push_back

#define mp make_pair

#define x first

#define y second

const int maxn = ;

ll n,m;

string s[maxn];

map<char, int> mmp;

int main()

{

    int t; cin >> t;

    while (t--) {

        cin >> n >> m;

        rep(i, , n)cin >> s[i];

        string ans ; ans.clear();

        int now = , mn = ;

        rep(j, , m-) {

            mmp.clear();

            rep(i, , n) {

                //cnt[s[i][j]]++;

                mmp[s[i][j]]++;

            }

            pair<char, int> temp = { 'Z',- };

            for (auto t : mmp)if (t.second > temp.second|| (t.second == temp.second&&t.first<temp.first))temp = t;

            ans.push_back(temp.first);

            mn += n -temp.second;

        }

        cout << ans << endl;

        cout << mn << endl;

    }

    cin >> n;

    return ;

}

/*

3

5 8

TATGATAC

TAAGCTAC

AAAGATCC

TGAGATAC

TAAGATGT

4 10

ACGTACGTAC

CCGTACGTAG

GCGTACGTAT

TCGTACGTAA

6 10

ATGTTACCAT

AAGTTACGAT

AACAAAGCAA

AAGTTACCTT

AAGTTACCAA

TACTTACCAA

*/