#include <bits/stdc++.h>
using namespace std;
bool compare(pair<int, int> a, pair<int, int> b) {
  if (a.first == b.first)
    return a.second < b.second;
  else
    return a.first < b.first;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int t = 1;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    vector<pair<int, int> > v;
    for (int i = 0; i < n; i++) {
      int a, b;
      cin >> a >> b;
      v.push_back({a, b});
    }
    sort(v.begin(), v.end(), compare);
    string s;
    int u = v[0].first;
    int r = v[0].second;
    while (u) {
      s += 'R';
      u--;
    }
    while (r) {
      s += 'U';
      r--;
    }
    bool flag = 0;
    for (int i = 1; i < n; i++) {
      int u = v[i].first - v[i - 1].first;
      int r = v[i].second - v[i - 1].second;
      if (u > -1 && r > -1) {
        while (u) {
          s += 'R';
          u--;
        }
        while (r) {
          s += 'U';
          r--;
        }
      } else {
        flag = 1;
        break;
      }
    }
    if (flag)
      cout << "NO" << endl;
    else
      cout << "YES" << endl << s << endl;
  }
  return 0;
}
