#include <bits/stdc++.h>
using namespace std;
const long long mod = 1000000007;
const long long inf = 1000000000000000000;
int main() {
  long long t;
  cin >> t;
  while (t--) {
    long long n;
    cin >> n;
    vector<pair<long long, long long> > p(n);
    for (auto& x : p) cin >> x.first >> x.second;
    sort(p.begin(), p.end());
    pair<long long, long long> now = {0, 0};
    bool f = 1;
    string ans = "";
    for (int i = 0; i < n; i++) {
      if (p[i].first >= now.first && p[i].second >= now.second) {
        long long r = p[i].first - now.first, u = p[i].second - now.second;
        while (r--) ans += 'R';
        while (u--) ans += 'U';
        now = p[i];
      } else {
        f = 0;
        break;
      }
    }
    if (f)
      cout << "YES\n" << ans << endl;
    else
      cout << "NO\n";
  }
  return 0;
}
