#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  int n, t;
  vector<pair<int, int>> v;
  cin >> t;
  while (t--) {
    v.clear();
    cin >> n;
    for (int i = 1; i <= n; i++) {
      int x, y;
      cin >> x >> y;
      v.push_back({x, y});
    }
    sort(v.begin(), v.end());
    int curX = 0, curY = 0;
    string ans = "";
    bool flag = 1;
    for (auto &it : v) {
      if (it.first < curX || it.second < curY) {
        flag = 0;
        break;
      }
      while (curX < it.first) {
        curX++;
        ans += 'R';
      }
      while (curY < it.second) {
        curY++;
        ans += 'U';
      }
    }
    if (!flag) {
      cout << "NO\n";
    } else {
      cout << "YES\n";
      cout << ans << "\n";
    }
  }
  return 0;
}
