#include <bits/stdc++.h>
using namespace std;
int main() {
  long long t, i, j, n, a, b, k;
  cin >> t;
  while (t--) {
    cin >> n;
    vector<vector<long long> > cd(n);
    for (i = 0; i < n; ++i) {
      cin >> a >> b;
      cd[i].push_back(a);
      cd[i].push_back(b);
    }
    sort(cd.begin(), cd.end());
    string s = "";
    i = 0, j = 0;
    for (k = 0; k < n; ++k) {
      if (i <= cd[k][0] && j <= cd[k][1]) {
        while (i < cd[k][0]) {
          s += "R";
          ++i;
        }
        while (j < cd[k][1]) {
          s += "U";
          ++j;
        }
      } else
        break;
    }
    if (k == n)
      cout << "YES" << endl << s << endl;
    else
      cout << "NO" << endl;
  }
  return 0;
}
