#include <bits/stdc++.h>   using namespace std;   int main(int argc, const char* argv[]) {     int cases;     cin >> cases;     while (cases--) {       int num;       scanf( %d , &num);       vector<pair<int, int> > coords;       pair<int, int> z(0, 0);       coords.push_back(z);       for (int i = 0; i < num; ++i) {         int x, y;         scanf( %d%d , &x, &y);         coords.push_back({x, y});       }       sort(coords.begin(), coords.end());       string out;       bool ok = true;       for (int i = 1; i <= num; ++i) {         int diffx = coords[i].first - coords[i - 1].first;         int diffy = coords[i].second - coords[i - 1].second;         if (diffx < 0 || diffy < 0) {           ok = false;           break;         }         while (diffx--) out +=  R ;         while (diffy--) out +=  U ;       }       if (ok) {         cout <<  YES  << endl;         cout << out << endl;       } else {         cout <<  NO  << endl;       }     }     return 0;   }   