#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    vector<pair<int, int>> a(n);
    for (int i = 0; i < n; i++) {
      cin >> a[i].first >> a[i].second;
    }
    sort(a.begin(), a.end());
    pair<int, int> cur = make_pair(0, 0);
    string str;
    int flag = 1;
    for (int i = 0; i < n; i++) {
      int r = a[i].first - cur.first;
      int u = a[i].second - cur.second;
      if (r < 0 || u < 0) {
        cout << "NO"
             << "\n";
        flag = 0;
        break;
      }
      cur = a[i];
      str += string(r, 'R');
      str += string(u, 'U');
    }
    if (flag)
      cout << "YES"
           << "\n"
           << str << "\n";
  }
  return 0;
}
