#include <bits/stdc++.h>
using namespace std;
int32_t main(void) {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long i, j;
  long long t;
  cin >> t;
  while (t--) {
    long long n;
    cin >> n;
    vector<pair<long long, long long> > arr;
    for (i = 0; i < n; i++) {
      long long x, y;
      cin >> x >> y;
      arr.push_back(make_pair(x, y));
    }
    sort(arr.begin(), arr.end());
    long long currX = 0;
    long long currY = 0;
    long long x, y;
    bool pig = false;
    string ans = "";
    for (auto i : arr) {
      x = i.first;
      y = i.second;
      if (y < currY) {
        cout << "NO"
             << "\n";
        pig = true;
        break;
      }
      while (currX < x) {
        ans += 'R';
        ++currX;
      }
      while (currY < y) {
        ans += 'U';
        ++currY;
      }
    }
    if (pig) continue;
    cout << "YES"
         << "\n";
    cout << ans << "\n";
  }
  return 0;
}
