#include <bits/stdc++.h>
using namespace std;
long long int t = 1;
void solve() {
  long long int i, j, k, a, b, n;
  cin >> n;
  vector<pair<long long int, long long int> > dizi(n);
  for (i = 0; i < n; i++) cin >> dizi[i].first >> dizi[i].second;
  sort(dizi.begin(), dizi.end());
  for (i = 1; i < n; i++) {
    if (dizi[i - 1].second > dizi[i].second) {
      cout << "NO" << endl;
      return;
    }
  }
  cout << "YES" << endl;
  j = 0;
  k = 0;
  for (i = 0; i < n; i++) {
    for (; j < dizi[i].first; j++) cout << "R";
    for (; k < dizi[i].second; k++) cout << "U";
  }
  cout << endl;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  cin >> t;
  while (t--) {
    solve();
  }
  return 0;
}
