// Java solution for problem K
// Author: Grzegorz Guspiel

import java.io.*;
import java.util.*;

public class k {
    static BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
    final int INF = 1100100100;

    int n = 26;
    boolean[][] adj = new boolean[n][]; {
        for (int i = 0; i < n; i++) adj[i] = new boolean[n];
        for (int i = 0; i < n; i++) for (int j = 0; j < n; j++) adj[i][j] = true;
    }
    int[] v = new int[n]; {
        for (int i = 0; i < n; i++) v[i] = 0;
    }
    int[] d = new int[n];
    int[] go = new int[n];

    void dfs(int a) {
        v[a] = 1;
        d[a] = 0;
        for (int i = 0; i < n; i++) if (adj[a][i]) {
            if (v[i] == 0) {
                dfs(i);
            } else if (v[i] == 1) {
                d[a] = INF;
                go[a] = i;
            }
            if (d[i] + 1 > d[a]) {
                d[a] = d[i] + 1;
                go[a] = i;
            }
        }
        v[a] = 2;
    }

    void solve() throws IOException {
        int cnt = Integer.parseInt(reader.readLine());
        for (int i = 0; i < cnt; i++) {
            String digraph = reader.readLine();
            adj[digraph.charAt(0) - 'a'][digraph.charAt(1) - 'a'] = false;
        } 

        for (int i = 0; i < n; i++) if (v[i] == 0) dfs(i);

        int s = 0;
        for (int i = 0; i < n; i++) if (d[i] > d[s]) s = i;

        String r = "";
        int letters = d[s] + 1;
        if (letters % 2 == 0) letters--;
        letters = Math.min(letters, 20 * 2 - 1);
        for (int i = 0; i < letters; i++) {
            r += (char)('a' + s);
            s = go[s];
        }
        
        int k = r.length() / 2 + 1; 
        for (int i = 0; i < k; i++) {
            StringBuilder line = new StringBuilder();
            for (int j = 0; j < k; j++) line.append(r.charAt(i + j));
            System.out.println(line.toString());
        }
    }

    public static void main(String[] args) throws IOException {
        int z = Integer.parseInt(reader.readLine());
        for (int zz = 0; zz < z; zz++) {
            new k().solve();
        }
    }
}