#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    pair<int, int> a[n];
    for (int i = 0; i < n; i++) {
      cin >> a[i].first >> a[i].second;
    }
    sort(a, a + n);
    int x = 0, y = 0, f = 0;
    string s = "";
    for (int i = 0; i < n; i++) {
      int u = a[i].first, v = a[i].second;
      if (v < y) {
        f = 1;
        cout << "NO";
        cout << endl;
        break;
      }
      s += string(u - x, 'R');
      s += string(v - y, 'U');
      x = u;
      y = v;
    }
    if (!f) cout << "YES" << endl << s << endl;
  }
  return 0;
}
