#include <bits/stdc++.h>   using namespace std;   pair<int, int> x[1024], y[1024];   int main() {     ios_base::sync_with_stdio(false);     cin.tie(NULL);     int t;     cin >> t;     while (t--) {       int n;       cin >> n;       for (int i = 0; i < n; i++) {         cin >> x[i].first >> x[i].second;         y[i].first = x[i].first;         y[i].second = x[i].second;       }       sort(x, x + n, [](const pair<int, int>& a, const pair<int, int>& b) {         return a.first < b.first || (a.first == b.first && a.second < b.second);       });       sort(y, y + n, [](const pair<int, int>& a, const pair<int, int>& b) {         return a.second < b.second || (a.second == b.second && a.first < b.first);       });       string ans =   ;       int r = 0, c = 0;       for (int i = 0; i < n; i++) {         if (x[i] != y[i]) {           cout <<  NO  << endl;           ans =   ;           break;         } else {           ans += string(x[i].first - r,  R );           ans += string(x[i].second - c,  U );           r = x[i].first;           c = x[i].second;         }       }       if (!ans.empty()) {         cout <<  YES  << endl << ans << endl;       }     }     return 0;   }   