#include <bits/stdc++.h>
using namespace std;
pair<long long, long long> p[2000003];
map<long long, long long> make_pair, m;
set<long long> st, ste;
vector<long long> vec, v;
bool bo[2000003];
int main() {
  ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
  int t, u;
  string str = "", s1 = "", s2 = "";
  char ch;
  long long d, ct = 0, q = 0, l, n = 0, k = 0, i, x = 0, y = 0, z = 0, j = 0,
               s = 0, r = 0;
  long long arr[2000003] = {0}, b[200003], c[200003], a[200003];
  double dr;
  cin >> t;
  while (t--) {
    s = k = r = j = x = y = 0;
    str = "", s1 = "";
    cin >> n;
    for (i = 0; i < n; i++) cin >> p[i].first >> p[i].second;
    sort(p, p + n);
    j = 0;
    i = 0;
    while (i < n) {
      k = p[i].first;
      l = p[i].second;
      if (l < x) {
        r = 1;
        break;
      }
      str += string(k - y, 'R');
      str += string(l - x, 'U');
      y = k;
      x = l;
      i++;
    }
    if (r == 1)
      cout << "NO";
    else
      cout << "YES\n" << str;
    cout << "\n";
  }
  return 0;
}
