#include <bits/stdc++.h>
using namespace std;
int main(int argc, const char* argv[]) {
  int cases;
  cin >> cases;
  while (cases--) {
    int num;
    scanf("%d", &num);
    pair<int, int> z(0, 0);
    vector<pair<int, int> > coords;
    coords.push_back(z);
    for (int i = 0; i < num; ++i) {
      int x, y;
      scanf("%d%d", &x, &y);
      coords.push_back({x, y});
    }
    sort(coords.begin(), coords.end());
    string out;
    bool ok = true;
    for (int i = 1; i <= num; ++i) {
      int diffx = coords[i].first - coords[i - 1].first;
      int diffy = coords[i].second - coords[i - 1].second;
      if (diffx < 0 || diffy < 0) {
        ok = false;
        break;
      }
      while (diffx--) out += 'R';
      while (diffy--) out += 'U';
    }
    if (ok) {
      cout << "YES" << endl;
      cout << out << endl;
    } else {
      cout << "NO" << endl;
    }
  }
  return 0;
}
