#include <bits/stdc++.h>
using namespace std;
const long long MOD = 1e9 + 7;
int main() {
  int t;
  scanf("%d", &t);
  while (t--) {
    int n;
    scanf("%d", &n);
    vector<char> tmp;
    vector<pair<int, int> > data;
    for (int i = 0; i < n; i++) {
      int x, y;
      scanf("%d%d", &x, &y);
      data.push_back(make_pair(y, x));
    }
    sort(data.begin(), data.end());
    bool ans = 1;
    int maks = 0, baris = 0;
    for (auto i : data) {
      if (maks > i.second) {
        ans = 0;
        break;
      }
      for (int j = 0; j < i.second - maks; j++) tmp.push_back('R');
      for (int j = 0; j < i.first - baris; j++) tmp.push_back('U');
      maks = i.second;
      baris = i.first;
    }
    if (ans) {
      printf("YES\n");
      for (auto i : tmp) cout << i;
      printf("\n");
    } else
      printf("NO\n");
  }
}
