#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  cin >> t;
  for (int j = 0; j < t; j++) {
    long long a, b, c, n, d, e, f;
    cin >> n;
    string s = "";
    pair<int, int> co[n];
    for (int i = 0; i < n; i++) {
      cin >> co[i].first >> co[i].second;
    }
    sort(co, co + n);
    d = co[0].first;
    e = co[0].second;
    for (a = 0; a < d; a++) s = s + 'R';
    for (a = 0; a < e; a++) s = s + 'U';
    int i;
    for (i = 1; i < n; i++) {
      if (co[i].first - co[i - 1].first < 0 ||
          co[i].second - co[i - 1].second < 0) {
        cout << "NO" << endl;
        break;
      } else {
        d = co[i].first - co[i - 1].first;
        e = co[i].second - co[i - 1].second;
        for (a = 0; a < d; a++) s = s + 'R';
        for (a = 0; a < e; a++) s = s + 'U';
      }
    }
    if (i == n) cout << "YES" << endl << s << endl;
  }
}
