code2155B.cpp

/*
 * Contest : Codeforces
 * Problem : 2155B - Abraham's Great Escape
 * Link    : https://codeforces.com/problemset/problem/2155/B
 */

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

#define fastio ios::sync_with_stdio(0); cin.tie(0);

vector<vector<bool>> escape;
int n, k;
unordered_map<char, pair<int, int>> dir = {
    {'U', {-1, 0}},
    {'D', {1, 0}},
    {'R', {0, 1}},
    {'L', {0, -1}},
};

bool validPos(int i, int j) {
  if (i >= 0 && i < n && j >= 0 && j < n) return true;
  return false;
}

void solve() {
  cin >> n >> k;

  if (n * n - 1 == k) {
    cout << "NO\n";
    return;
  }
  else if (n * n == k) {
    cout << "YES\n";
    for (int i = 0; i < n; ++i) {
      for (int j = 0; j < n; ++j) { cout << "U"; }
      cout << '\n';
    }
    return;
  }

  cout << "YES\n";

  escape.assign(n, vector<bool>(n, false));
  int cnt = 0;
  for (int i = 0; i < n; ++i) {
    for (int j = 0; j < n; ++j) {
      for (auto &[c, d] : dir) {
        int x = i + d.first,
            y = j + d.second;

        if (cnt < k) {
          if (x < 0 || x >= n || y < 0 || y >= n) {
            cout << c;
            escape[i][j] = true;
            cnt++;
          }
          else if (validPos(x, y) && escape[x][y]) {
            cout << c;
            escape[i][j] = true;
            cnt++;
          }
          break;
        }
        else {
          if (validPos(x, y) && !escape[x][y]) {
            cout << c;
            break;
          }
        }
      }
    }
    cout << '\n';
  }
}

int main() {
  fastio

  int tc; cin >> tc;
  while (tc--) solve();

  return 0;
}