#include <bits/stdc++.h>
using namespace std;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int Tc;
    cin >> Tc;
    while (Tc--) {
        int N, M;
        cin >> N >> M;
        vector<string> T(N);
        for (int i = 0; i < N; ++i) {
            cin >> T[i];
        }

        // Count frequency of each string
        unordered_map<string, int> freq;
        for (const string& s : T) {
            freq[s]++;
        }

        // Find the most frequent string
        string S_initial;
        int max_freq = 0;
        for (const auto& [s, cnt] : freq) {
            if (cnt > max_freq) {
                max_freq = cnt;
                S_initial = s;
            }
        }

        // Calculate score if no change is made
        int score_no_change = 0;
        for (const string& s : T) {
            if (s == S_initial) {
                score_no_change += M;
            } else {
                for (int j = 0; j < M; ++j) {
                    if (s[j] == S_initial[j]) {
                        score_no_change++;
                    }
                }
            }
        }

        // Calculate score if change is made
        int max_score = score_no_change;
        for (int i = 0; i < N; ++i) {
            string S_new = T[i];
            int score_change = 0;
            for (int k = 0; k < N; ++k) {
                if (k <= i) {
                    // Before change, use S_initial
                    if (T[k] == S_initial) {
                        score_change += M;
                    } else {
                        for (int j = 0; j < M; ++j) {
                            if (T[k][j] == S_initial[j]) {
                                score_change++;
                            }
                        }
                    }
                } else {
                    // After change, use S_new
                    if (T[k] == S_new) {
                        score_change += M;
                    } else {
                        for (int j = 0; j < M; ++j) {
                            if (T[k][j] == S_new[j]) {
                                score_change++;
                            }
                        }
                    }
                }
            }
            max_score = max(max_score, score_change);
        }

        cout << max_score << "\n";
    }

    return 0;
}