#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(), cout.tie(NULL), cin.tie(NULL);
  ;
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    map<pair<int, int>, int> m;
    for (int i = 0; i < n; i++) {
      int x, y;
      cin >> x >> y;
      m[make_pair(x, y)] = 1;
    }
    string s = "";
    int curx = 0;
    int cury = 0;
    bool flag = true;
    for (auto x : m) {
      int a = x.first.first;
      int b = x.first.second;
      if (a >= curx) {
        while (curx < a) {
          s += 'R';
          curx++;
        }
      } else {
        flag = false;
        break;
      }
      if (b >= cury) {
        while (cury < b) {
          s += "U";
          cury++;
        }
      } else {
        flag = false;
        break;
      }
    }
    if (flag) {
      cout << "YES" << endl;
      cout << s << endl;
    } else
      cout << "NO" << endl;
  }
  return 0;
}
