#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  int q;
  cin >> q;
  while (q--) {
    int n;
    cin >> n;
    vector<pair<int, int> > v;
    v.push_back(make_pair(0, 0));
    for (int i = 1; i <= n; i++) {
      int x, y;
      cin >> x >> y;
      v.push_back(make_pair(y, x));
    }
    sort(v.begin(), v.end());
    bool flag = true;
    for (int i = 1; i <= n; i++) {
      if (v[i].second < v[i - 1].second) {
        flag = false;
      }
    }
    if (!flag) {
      cout << "NO" << endl;
      continue;
    }
    string t = "";
    for (int i = 1; i <= n; i++) {
      int dx = v[i].second - v[i - 1].second;
      int dy = v[i].first - v[i - 1].first;
      while (dx--) t += 'R';
      while (dy--) t += 'U';
    }
    cout << "YES" << endl;
    cout << t << endl;
  }
  return 0;
}
