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