//#pragma GCC optimize(3, "Ofast", "inline")
#include <bits/stdc++.h>

using namespace std;

#define endl "\n"
//#define int long long

typedef long long ll;
typedef unsigned long long ull;
typedef long double db;
typedef pair<int, int> pii;
typedef array<int, 3> piii;
typedef vector<int> vi;
typedef vector<vector<int>> vii;

const int N = 160 * 160, inf = 0x3f3f3f3f, mod = 998244353;

int n;
pii cnt[N];
pii t[N];
int ans[N];
map<pii, int> mp;
unordered_map<int, int> ump;
map<pii, vi> pkc;
map<pii, pii> pkk;
vector<string> all;
//char, int
vector<pii> pkres;
vector<pii> tcnt;
// vi pkc49;
vi pk49 = {25, 26, 27};
bool vis[3];

bool check()
{
    vector<string> tmp;
    auto tump = ump;
    // for (int i = 0; i < pkres.size(); i++)
    //     cerr << char(pkres[i].first) << " " << pkres[i].second << endl;
    for (int i = 0; i < pkres.size(); i++)
        tump[pkres[i].first] = pkres[i].second;
    for (int i = 0; i < 128; i++)
        ans[i] = 0;
    // cerr << ump[31] << endl;
    for (auto [k, v] : tump)
        if (v >= 0)
            ans[v] = k;
    // for (int i = 0; i < n; i++)
    //     cerr << char(ans[i]);
    for (int i = 0; i < n; i++)
        for (int j = 0; j < n; j++)
        {
            int x = i * j;
            string ts;
            if (i * j >= n)
                ts.push_back(ans[i * j / n]);
            ts.push_back(ans[i * j % n]);
            tmp.push_back(ts);
        }
    sort(tmp.begin(), tmp.end());
    return tmp == all;
}

bool dfs(int u)
{
    if (u == tcnt.size())
        return check();
    if (pkc[tcnt[u]].size() == 3)
    {
        pkres.push_back({pkc[tcnt[u]][0], pk49[0]});
        pkres.push_back({pkc[tcnt[u]][1], pk49[1]});
        pkres.push_back({pkc[tcnt[u]][2], pk49[2]});
        if (dfs(u + 1))
            return true;
        pkres.pop_back(), pkres.pop_back(), pkres.pop_back();

        pkres.push_back({pkc[tcnt[u]][0], pk49[0]});
        pkres.push_back({pkc[tcnt[u]][1], pk49[2]});
        pkres.push_back({pkc[tcnt[u]][2], pk49[1]});
        if (dfs(u + 1))
            return true;
        pkres.pop_back(), pkres.pop_back(), pkres.pop_back();

        pkres.push_back({pkc[tcnt[u]][0], pk49[1]});
        pkres.push_back({pkc[tcnt[u]][1], pk49[0]});
        pkres.push_back({pkc[tcnt[u]][2], pk49[2]});
        if (dfs(u + 1))
            return true;
        pkres.pop_back(), pkres.pop_back(), pkres.pop_back();

        pkres.push_back({pkc[tcnt[u]][0], pk49[1]});
        pkres.push_back({pkc[tcnt[u]][1], pk49[2]});
        pkres.push_back({pkc[tcnt[u]][2], pk49[0]});
        if (dfs(u + 1))
            return true;
        pkres.pop_back(), pkres.pop_back(), pkres.pop_back();

        pkres.push_back({pkc[tcnt[u]][0], pk49[2]});
        pkres.push_back({pkc[tcnt[u]][1], pk49[1]});
        pkres.push_back({pkc[tcnt[u]][2], pk49[0]});
        if (dfs(u + 1))
            return true;
        pkres.pop_back(), pkres.pop_back(), pkres.pop_back();

        pkres.push_back({pkc[tcnt[u]][0], pk49[2]});
        pkres.push_back({pkc[tcnt[u]][1], pk49[0]});
        pkres.push_back({pkc[tcnt[u]][2], pk49[1]});
        if (dfs(u + 1))
            return true;
        pkres.pop_back(), pkres.pop_back(), pkres.pop_back();

        return false;
    }
    pkres.push_back({pkc[tcnt[u]][0], pkk[tcnt[u]].first});
    pkres.push_back({pkc[tcnt[u]][1], pkk[tcnt[u]].second});
    if (dfs(u + 1))
        return true;
    pkres.pop_back(), pkres.pop_back();
    pkres.push_back({pkc[tcnt[u]][0], pkk[tcnt[u]].second});
    pkres.push_back({pkc[tcnt[u]][1], pkk[tcnt[u]].first});
    if (dfs(u + 1))
        return true;
    pkres.pop_back(), pkres.pop_back();
    return false;
}

void init()
{
    for (int i = 0; i < n; i++)
        cnt[i] = {0, 0}, ans[i] = 0;
    for (int i = 0; i < 128; i++)
        t[i] = {0, 0};
    for (int i = 0; i < n; i++)
        for (int j = 0; j < n; j++)
            cnt[i * j % n].second++, cnt[i * j / n].first++;
    for (int i = 0; i < 3; i++)
        vis[i] = false;
    mp.clear();
    ump.clear();
    pkk.clear();
    pkc.clear();
    pkres.clear();
    tcnt.clear();
    all.clear();
    for (int i = 0; i < n; i++)
    {
        if (mp.count(cnt[i]))
        {
            pkk[cnt[i]] = {mp[cnt[i]], i};
            mp[cnt[i]] = -1;
            tcnt.push_back(cnt[i]);
            continue;
        }
        mp[cnt[i]] = i;
    }
}

signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr), cout.tie(nullptr);
    int T;
    cin >> T;
    while (T--)
    {
        cin >> n;
        init();
        string s;
        for (int i = 0; i < n * n; i++)
        {
            cin >> s;
            // cerr << n << endl;
            all.push_back(s);
            // cerr << n << " ok\n";
            if (s.size() == 1)
                t[s[0]].second++;
            else
                t[s[0]].first++, t[s[1]].second++;
        }
        sort(all.begin(), all.end());
        for (int i = 0; i < 128; i++)
        {
            if (t[i] == make_pair(0, 0))
                continue;
            if (mp[t[i]] == -1)
            {
                pkc[t[i]].push_back(i);
                continue;
            }
            ump[i] = mp[t[i]];
        }
        dfs(0);
        for (int i = 0; i < n; i++)
            cout << char(ans[i]);
        cout << endl;
    }
    return 0;
}