#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int t;
  cin >> t;
  while (t--) {
    long long int n;
    cin >> n;
    long long int c = 0;
    vector<vector<int> > v(n);
    for (long long int i = 0; i < n; i++) {
      long long int x, y;
      cin >> x >> y;
      v[i].push_back(x);
      v[i].push_back(y);
    }
    sort(v.begin(), v.end());
    long long int dif1 = 0;
    long long int dif2 = 0;
    string s;
    long long int mini1 = INT_MIN;
    long long int mini2 = INT_MIN;
    for (long long int i = 0; i < n; i++) {
      if (v[i][0] > mini1) {
        for (long long int j = 0; j < (v[i][0] - dif1); j++) {
          s.push_back('R');
        }
        dif1 = v[i][0];
      }
      if (v[i][0] < mini1) {
        cout << "NO" << endl;
        c++;
        break;
      }
      mini1 = v[i][0];
      if (v[i][1] > mini2) {
        for (long long int j = 0; j < (v[i][1] - dif2); j++) {
          s.push_back('U');
        }
        dif2 = v[i][1];
      }
      if (v[i][1] < mini2) {
        cout << "NO" << endl;
        c++;
        break;
      }
      mini2 = v[i][1];
    }
    if (c == 0) {
      cout << "YES" << endl;
      cout << s << endl;
    }
  }
  return 0;
}
