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