#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  cin >> t;
  while (t--) {
    long long n;
    cin >> n;
    vector<pair<int, int> > dis;
    for (int i = 0; i < n; i++) {
      int a, b;
      cin >> a >> b;
      dis.push_back(make_pair(a, b));
    }
    sort(dis.begin(), dis.end());
    pair<int, int> p = {0, 0};
    string ans = "";
    bool flag = true;
    for (int i = 0; i < n; i++) {
      if ((dis[i].first > p.first && dis[i].second > p.second) ||
          (dis[i].first > p.first && dis[i].second == p.second) ||
          (dis[i].first == p.first && dis[i].second > p.second)) {
        int k = dis[i].first - p.first;
        while (k--) {
          ans += 'R';
        }
        k = dis[i].second - p.second;
        while (k--) {
          ans += 'U';
        }
        p = dis[i];
      } else {
        flag = false;
        break;
      }
    }
    if (flag) {
      cout << "YES" << endl;
      cout << ans << endl;
    } else {
      cout << "NO" << endl;
    }
  }
}
