#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    vector<pair<int, int> > v;
    v.push_back(make_pair(0, 0));
    for (int i = 0; i < n; i++) {
      int a, b;
      cin >> a >> b;
      v.push_back(make_pair(a, b));
    }
    sort(v.begin(), v.end());
    bool flag = false;
    string res;
    for (int i = 0; i < n; i++) {
      if (v[i + 1].first < v[i].first) {
        cout << "NO" << endl;
        flag = true;
        break;
      }
      if (v[i + 1].first > v[i].first) {
        int k = v[i + 1].first - v[i].first;
        while (k--) {
          res += "R";
        }
      }
      if (v[i + 1].second < v[i].second) {
        cout << "NO" << endl;
        flag = true;
        break;
      }
      if (v[i + 1].second > v[i].second) {
        int kk = v[i + 1].second - v[i].second;
        while (kk--) {
          res += "U";
        }
      }
    }
    if (!flag) {
      cout << "YES" << endl;
      cout << res << endl;
    }
  }
}
