#include <bits/stdc++.h>
using namespace std;
void solve() {
  int n;
  cin >> n;
  vector<pair<int, int> > a(n);
  for (int i = 0; i < n; i++) cin >> a[i].first >> a[i].second;
  sort(a.begin(), a.end());
  string ans = "";
  if (n == 1) {
    while (a[0].first--) ans += 'R';
    while (a[0].second--) ans += 'U';
    cout << "YES\n" << ans << '\n';
    return;
  }
  for (int i = 0; i < n; i++) {
    if (a[i].second > a[i + 1].second && i < n - 1) {
      cout << "NO\n";
      return;
    } else {
      int k;
      if (i == 0)
        k = a[i].first;
      else
        k = a[i].first - a[i - 1].first;
      while (k--) ans += 'R';
      if (i == 0)
        k = a[i].second;
      else
        k = a[i].second - a[i - 1].second;
      while (k--) ans += 'U';
    }
  }
  cout << "YES\n" << ans << '\n';
}
int main() {
  int t;
  cin >> t;
  while (t--) solve();
}
