#include <bits/stdc++.h>
using namespace std;
int main() {
  int test;
  cin >> test;
  while (test--) {
    int num;
    cin >> num;
    vector<pair<int, int>> arr;
    vector<pair<int, int>> arr2;
    for (int i = 0; i < num; i++) {
      int a, b;
      cin >> a >> b;
      arr.push_back(make_pair(a, b));
    }
    sort(arr.begin(), arr.end());
    string s;
    pair<int, int> curr = {0, 0};
    bool ok = true;
    for (int j = 0; j < num; j++) {
      int r = arr[j].first - curr.first;
      int u = arr[j].second - curr.second;
      if (r < 0 || u < 0) {
        cout << "NO"
             << "\n";
        ok = false;
        break;
      }
      s += string(r, 'R');
      s += string(u, 'U');
      curr = arr[j];
    }
    if (ok) {
      cout << "YES"
           << "\n";
      cout << s << "\n";
    }
  }
}
