#include <bits/stdc++.h>
using namespace std;
long long q, n;
vector<pair<long long, long long> > v;
string s;
bool test;
int main() {
  cin >> q;
  while (q--) {
    cin >> n;
    v.push_back({0, 0});
    for (int i = 0; i < n; i++) {
      long long x, y;
      cin >> x >> y;
      v.push_back({x, y});
    }
    sort(v.begin(), v.end());
    for (int i = 1; i < v.size(); i++) {
      if (v[i].first >= v[i - 1].first && v[i].second >= v[i - 1].second) {
        for (int j = 0; j < v[i].first - v[i - 1].first; j++) s += 'R';
        for (int j = 0; j < v[i].second - v[i - 1].second; j++) s += 'U';
      } else {
        test = true;
        break;
      }
    }
    if (test) {
      cout << "NO" << endl;
    } else {
      cout << "YES" << endl << s << endl;
    }
    v.clear();
    test = false;
    s = "";
  }
  return 0;
}
