#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--) {
    int n;
    cin >> n;
    vector<pair<long long, long long>> v;
    for (long long i = 0; i < n; i++) {
      int a, b;
      cin >> a >> b;
      v.emplace_back(make_pair(a, b));
    }
    sort(v.begin(), v.end());
    int x = 0, y = 0, k = 0;
    string ans = "";
    for (long long i = 0; i < n; i++) {
      int a, b;
      a = v[i].first - x;
      b = v[i].second - y;
      if (a < 0 || b < 0) {
        k = 1;
        break;
      }
      for (long long i = 0; i < a; i++) ans += 'R';
      for (long long i = 0; i < b; i++) ans += 'U';
      x = v[i].first;
      y = v[i].second;
    }
    if (k) {
      cout << "NO\n";
    } else
      cout << "YES\n" << ans << endl;
  }
}
