#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int t;
  cin >> t;
  while (t--) {
    vector<pair<int, int>> v;
    int a, x = 0, y = 0, f = 0, ans, n = 0;
    cin >> a;
    for (int i = 0; i < a; i++) {
      int s, p;
      cin >> s >> p;
      v.push_back(make_pair(s, p));
    }
    sort(v.begin(), v.end());
    int xx = 0, yy = 0;
    string s = "";
    for (int i = 0; i < a; i++) {
      xx = v[i].first - xx;
      yy = v[i].second - yy;
      if (xx < 0 || yy < 0) {
        f = 1;
        cout << "NO"
             << "\n";
        break;
      }
      for (int i = 0; i < xx; i++) s += "R";
      for (int i = 0; i < yy; i++) s += "U";
      xx = v[i].first;
      yy = v[i].second;
    }
    if (f == 1) continue;
    cout << "YES"
         << "\n";
    cout << s << "\n";
  }
  return 0;
}
