#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  cin >> t;
  while (t--) {
    int n, a, b, x = 0, y = 0, flag = 0;
    cin >> n;
    vector<pair<int, int> > v;
    string ans = "";
    for (int i = 0; i < n; i++) {
      cin >> a >> b;
      v.push_back(make_pair(a, b));
    }
    sort(v.begin(), v.end());
    for (int i = 0; i < n; i++) {
      if (v[i].second < y) {
        flag = 1;
        break;
      } else {
        for (int j = 0; j < v[i].first - x; j++) ans += 'R';
        for (int j = 0; j < v[i].second - y; j++) ans += 'U';
        x = v[i].first;
        y = v[i].second;
      }
    }
    if (flag)
      cout << "NO\n";
    else {
      cout << "YES\n";
      cout << ans << endl;
    }
  }
  return 0;
}
