#include <bits/stdc++.h>
using namespace std;
void pr_init() {}
void solve() {
  long long t;
  cin >> t;
  for (long long i = 0; i < t; i++) {
    long long n, ok = 1;
    cin >> n;
    string s = "";
    map<long long, set<long long> > cor;
    for (long long j = 0; j < n; j++) {
      long long u, v;
      cin >> u >> v;
      cor[u].insert(v);
    }
    long long px = 0, py = 0;
    for (auto x : cor) {
      for (long long k = 0; k < (x.first - px); k++) {
        s += 'R';
      }
      for (auto y : x.second) {
        if (y < py) {
          ok = 0;
          break;
        }
        for (long long k = 0; k < (y - py); k++) {
          s += 'U';
        }
        py = y;
      }
      if (!ok) break;
      px = x.first;
    }
    if (!ok) {
      cout << "NO\n";
      continue;
    }
    cout << "YES\n";
    cout << s << endl;
  }
}
int32_t main() {
  solve();
  return 0;
}
