#include <bits/stdc++.h>
const int Z = (int)1e3 + 123;
const int inf = (int)1e9 + 123;
const long long llinf = (long long)1e18 + 123;
using namespace std;
map<int, pair<int, int> > a;
int main() {
  int t;
  cin >> t;
  while (t--) {
    a.clear();
    int n, posx = 0, posy = 0;
    cin >> n;
    string ans;
    set<int> sum;
    bool flag = true;
    while (n--) {
      int x, y;
      cin >> x >> y;
      if (sum.count(x + y) > 0) {
        flag = false;
      }
      sum.insert(x + y);
      a[x + y] = {x, y};
    }
    if (flag == false) {
      cout << "NO \n";
      continue;
    }
    for (auto i : a) {
      if (posx > i.second.first || posy > i.second.second) {
        flag = false;
        break;
      }
      for (int q = posx; q < i.second.first; q++) {
        ans += 'R';
      }
      for (int q = posy; q < i.second.second; q++) {
        ans += 'U';
      }
      posx = i.second.first;
      posy = i.second.second;
    }
    if (flag) {
      cout << "YES \n" << ans << "\n";
    } else {
      cout << "NO \n";
    }
  }
  return 0;
}
