#include <bits/stdc++.h>
using namespace std;
const int inf = 2e9;
int main() {
  int t;
  cin >> t;
  for (int zz = 0; zz < t; zz++) {
    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> pos = {0, 0};
    string ans = "";
    bool f = true;
    for (int i = 0; i < n; i++) {
      pair<int, int> pt = a[i];
      if (pt.first < pos.first || pt.second < pos.second) {
        f = false;
        break;
      }
      for (int j = 0; j < pt.first - pos.first; j++) {
        ans += 'R';
      }
      for (int j = 0; j < pt.second - pos.second; j++) ans += 'U';
      pos = pt;
    }
    if (f) {
      cout << "YES" << endl << ans << endl;
    } else
      cout << "NO" << endl;
  }
}
