#include <bits/stdc++.h>
using namespace std;
void Ali() {
  std::ios_base::sync_with_stdio(0);
  cin.tie(NULL);
  cout.tie(NULL);
}
long long gcd(long long a, long long b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
int main() {
  Ali();
  long long tt;
  cin >> tt;
  while (tt--) {
    long long n, a, b, i = 0, j = 0;
    string s = "";
    bool c = false;
    vector<pair<long long, long long>> v;
    cin >> n;
    for (int i = 0; i < n; i++) {
      cin >> a >> b;
      v.push_back(make_pair(a, b));
    }
    sort(v.begin(), v.end());
    for (int l = 0; l < v.size(); l++) {
      if (v[l].first >= i && v[l].second >= j) {
        for (int k = 0; k < v[l].first - i; k++) s += "R";
        for (int k = 0; k < v[l].second - j; k++) s += "U";
        i = v[l].first;
        j = v[l].second;
      } else {
        c = true;
        break;
      }
    }
    if (c) {
      cout << "NO\n";
    } else {
      cout << "YES\n" << s << "\n";
    }
  }
}
