#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int t;
  cin >> t;
  while (t--) {
    vector<pair<int, int> > a;
    int n;
    cin >> n;
    int k = n;
    while (k--) {
      int x, y;
      cin >> x >> y;
      a.push_back(make_pair(x, y));
    }
    sort(a.begin(), a.end());
    string ans;
    int count = 0;
    int r = 0, u = 0;
    for (int i = 0; i < n; i++) {
      int n = a[i].first - r;
      while (n--) {
        ans.push_back('R');
      }
      r = a[i].first;
      int k = a[i].second - u;
      if (k < 0) {
        count++;
        break;
      } else {
        while (k--) {
          ans.push_back('U');
        }
        u = a[i].second;
      }
    }
    if (count != 0)
      cout << "NO" << endl;
    else {
      cout << "YES" << endl;
      cout << ans << endl;
    }
  }
  return 0;
}
