#include <bits/stdc++.h>
using namespace std;
bool comparePair(pair<int, int> a, pair<int, int> b) {
  if (a.first != b.first) return a.first < b.first;
  return a.second < b.second;
}
int main() {
  int T;
  cin >> T;
  for (int i = 0; i < T; i++) {
    int n;
    cin >> n;
    pair<int, int> points[n];
    bool isFine = true;
    for (int k = 0; k < n; k++) {
      int x, y;
      cin >> x >> y;
      if (x < 0 || y < 0) {
        isFine = false;
        break;
      }
      points[k] = make_pair(x, y);
    }
    if (isFine == false) {
      cout << "NO" << endl;
      continue;
    }
    sort(points, points + n, comparePair);
    string path = "";
    int toCollect = 0, x = 0, y = 0;
    isFine = true;
    while (toCollect != n) {
      if (points[toCollect].first < x || points[toCollect].second < y) {
        cout << "NO" << endl;
        isFine = false;
        break;
      }
      while (points[toCollect].first > x) {
        path += "R";
        x++;
      }
      while (points[toCollect].second > y) {
        path += "U";
        y++;
      }
      toCollect++;
    }
    if (isFine) {
      cout << "YES" << endl;
      cout << path << endl;
    }
  }
  return 0;
}
