#include <bits/stdc++.h>
using namespace std;
void solve() {
  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());
  int cx = 0, cy = 0;
  string ans = "";
  for (auto e : a) {
    if (e.first < cx || e.second < cy) {
      cout << "NO" << '\n';
      return;
    }
    int rs = e.first - cx;
    for (int i = 0; i < rs; i++) {
      ans += 'R';
    }
    int us = e.second - cy;
    for (int i = 0; i < us; i++) {
      ans += 'U';
    }
    cx = e.first;
    cy = e.second;
  }
  cout << "YES\n";
  cout << ans << '\n';
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int t;
  cin >> t;
  while (t--) {
    solve();
  }
  return 0;
}
