#include <bits/stdc++.h>
#ifdef dbg
#define D(...) fprintf(stderr, __VA_ARGS__)
#define DD(...) D(#__VA_ARGS__ " = "), debug_helper::debug(__VA_ARGS__), D("\n")
#include "C:\Users\wsyear\Desktop\OI\templates\debug.hpp"
#else
#define D(...) ((void)0)
#define DD(...) ((void)0)
#endif
#define rep(i, j, k) for (int i = (j); i <= (k); ++i)
#define per(i, j, k) for (int i = (j); i >= (k); --i)
#define SZ(v) int((v).size())
#define ALL(v) (v).begin(),(v).end()
#define fi first
#define se second
using ll = long long;
using pii = std::pair<int, int>;
using pll = std::pair<ll, ll>;

using namespace std;

const int maxn = 10000;

int n, tot;
char asp[maxn];
pii cnt[maxn];
map<char, int> cmk;
map<char, pii> ccnt;
map<pii, vector<int>> mp;
map<pii, vector<char>> cat;
string str[maxn];
vector<int> rea[maxn];
vector<char> cara[maxn];

void add(int x) {
  cnt[x % n].se++;
  if (x >= n) cnt[x / n].fi++;
}

bool check() {
  vector<int> cxy;
  rep (i, 1, n * n) {
    int val = 0;
    if (SZ(str[i]) == 2) {
      val = n * cmk[str[i][0]] + cmk[str[i][1]];
    } else {
      val = cmk[str[i][0]];
    }
    cxy.emplace_back(val);
  }
  vector<int> shz;
  rep (i, 0, n - 1) rep (j, 0, n - 1) shz.emplace_back(i * j);
  sort(ALL(cxy)), sort(ALL(shz));
  rep (i, 0, n * n - 1) if (cxy[i] != shz[i]) return 0;
  return 1;
}

void dfs(int dep) {
  if (dep > tot) {
    if (check()) {
      for (auto [x, y] : cmk) asp[y] = x;
    }
    return;
  }
  vector<int> p;
  rep (i, 0, SZ(rea[dep]) - 1) p.emplace_back(i);
  do {
    rep (i, 0, SZ(rea[dep]) - 1) cmk[cara[dep][i]] = rea[dep][p[i]];
    dfs(dep + 1);
  } while (next_permutation(ALL(p)));
}

void work() {
  cin >> n;
  rep (i, 1, n * n) cin >> str[i];
  mp.clear();
  rep (i, 0, n - 1) cnt[i] = pii(0, 0);
  rep (i, 0, n - 1) rep (j, 0, n - 1) add(i * j);
  rep (i, 0, n - 1) mp[cnt[i]].emplace_back(i);
  ccnt.clear();
  rep (i, 1, n * n) {
    if (SZ(str[i]) == 2) {
      ccnt[str[i][0]].fi++;
      ccnt[str[i][1]].se++;
    } else {
      ccnt[str[i][0]].se++;
    }
  }
  cat.clear();
  for (auto [cha, val] : ccnt) cat[val].emplace_back(cha);
  tot = 0;
  for (auto [cc, val] : mp) rea[++tot] = val;
  tot = 0;
  for (auto [cc, val] : cat) cara[++tot] = val;
  cmk.clear(), dfs(1);
  rep (i, 0, n - 1) cout << asp[i];
  cout << "\n";
}

int main() {
  cin.tie(nullptr) -> ios::sync_with_stdio(false);
  int t; cin >> t;
  while (t--) work();
}