#include <bits/stdc++.h>
using namespace std;
static bool sortbysec(const pair<int, int> &a, const pair<int, int> &b) {
  return (a.second < b.second);
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(NULL);
  long long int t;
  cin >> t;
  while (t--) {
    long long int n;
    cin >> n;
    vector<pair<int, int> > vect;
    long long int x, y;
    for (long long int i = 0; i < n; i++) {
      cin >> x >> y;
      vect.push_back(make_pair(x, y));
    }
    sort(vect.begin(), vect.end(), sortbysec);
    sort(vect.begin(), vect.end());
    vect.insert(vect.begin(), make_pair(0, 0));
    long long int i = 0, temp = 0;
    while (i <= (n - 1)) {
      if (vect[i].first > vect[i + 1].first) {
        temp = 1;
        break;
      } else if (vect[i].second > vect[i + 1].second) {
        temp = 1;
        break;
      }
      i++;
    }
    i = 0;
    if (temp != 1) {
      cout << "YES\n";
      while (i <= (n - 1)) {
        for (long long int j = 0; j < vect[i + 1].first - vect[i].first; j++)
          cout << "R";
        for (long long int j = 0; j < vect[i + 1].second - vect[i].second; j++)
          cout << "U";
        i++;
      }
      cout << endl;
    } else
      cout << "NO\n";
  }
}
