#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int t;
  cin >> t;
  while (t-- > 0) {
    int n;
    cin >> n;
    vector<pair<int, int> > v;
    while (n-- > 0) {
      int x, y;
      cin >> x;
      cin >> y;
      v.push_back(make_pair(x, y));
    }
    sort(v.begin(), v.end());
    string ans = "";
    int f = 1;
    int a = 0, b = 0;
    for (int i = 0; i < v.size(); i++) {
      int r = v[i].first - a;
      int u = v[i].second - b;
      a = v[i].first;
      b = v[i].second;
      if (r < 0 || u < 0) {
        f = 0;
        break;
      } else {
        for (int i = 0; i < r; i++) {
          ans += 'R';
        }
        for (int i = 0; i < u; i++) {
          ans += 'U';
        }
      }
    }
    if (f == 1) {
      cout << "YES" << endl;
      cout << ans << endl;
    } else {
      cout << "NO" << endl;
    }
  }
}
