#include <bits/stdc++.h>
using namespace std;
void shikhar7s(long long int cas) {
  long long int n, i;
  cin >> n;
  long long int maxi[1005], mini[1005];
  for (i = 0; i < 1005; i++) {
    maxi[i] = -1000000007;
    mini[i] = 1000000007;
  }
  vector<pair<long long int, long long int> > v, ch;
  long long int x, y;
  for (i = 0; i < n; i++) {
    cin >> x >> y;
    v.push_back(make_pair(x, y));
    if (maxi[x] < y) maxi[x] = y;
    if (mini[x] > y) {
      mini[x] = y;
    }
  }
  for (i = 0; i < 1005; i++) {
    if (mini[i] != 1000000007) ch.push_back(make_pair(maxi[i], mini[i]));
  }
  for (i = 0; i < (long long int)ch.size() - 1; i++) {
    if (ch[i].first > ch[i + 1].second) {
      cout << "NO"
           << "\n";
      return;
    }
  }
  cout << "YES"
       << "\n";
  sort(v.begin(), v.end());
  long long int j = 0, k = 0;
  for (i = 0; i < n; i++) {
    for (j = j; j < v[i].first; j++) cout << 'R';
    for (k = k; k < v[i].second; k++) cout << 'U';
  }
  cout << "\n";
}
signed main() {
  std::ios_base::sync_with_stdio(false);
  long long int t = 1;
  cin >> t;
  long long int cas = 1;
  while (cas <= t) {
    shikhar7s(cas);
    cas++;
  }
  return 0;
}
