#include <bits/stdc++.h>
using namespace std;
pair<int, int> a[1000000];
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    for (int i = 1; i <= n; i++) cin >> a[i].first >> a[i].second;
    sort(a + 1, a + n + 1);
    int x = 0, y = 0;
    bool ok = 1;
    string ret = "";
    for (int i = 1; i <= n; i++) {
      if (x > a[i].first || y > a[i].second) ok = 0;
      if (!ok) break;
      while (x < a[i].first) ret += "R", x++;
      while (y < a[i].second) ret += "U", y++;
    }
    if (!ok)
      cout << "NO" << endl;
    else
      cout << "YES" << endl << ret << endl;
  }
}
