#include<bits/stdc++.h>
using namespace std;

typedef pair<int, int>P;

bool cmp(P f, P s){
    if(f.first > s.first) return 0;
    if(f.first == s.first){
        if(f.second > s.second) return 0;
        else return 1;
    }else return 1;
}

int main()
{
    int casee;
    cin >> casee;
    while(casee--)
    {
        int n;
        char str[1000000];
        int c=0;
        cin >> n;
        vector< pair<int, int> > vec;
        for(int i = 0; i < n; i++)
        {
            int x, y;
            cin >> x >> y;
            vec.push_back(make_pair(x, y));
        }
        sort(vec.begin(), vec.end(), cmp);

        int xx=0,yy=0,d=0,ck=0;

        for(int i=0;i<n;i++)
        {
            int x,y;
            x = vec[i].first;
            y = vec[i].second;

            if(x<xx)
            {
                ck=1;
                break;
            }
            if(y<yy)
            {
                ck=1;
                break;
            }
            if(xx<x)
            {
                int h=x-xx;
                while(h--)
                {
                    str[c++] = 'R';
                }
                xx=x;
            }

            if(x==xx)
            {
                if(yy>y)
                {
                    ck=1;
                    break;
                }
                else{
                    int h=y-yy;
                    while(h--)
                    {
                        str[c++] = 'U';
                    }
                    yy=y;
                }
            }
        }

        str[c]='\0';
        if(ck==1)
        {
            cout<<"NO"<<endl;
        }
        else{
            cout<<"YES"<<endl;
            cout<<str<<endl;
        }
    }
    return 0;
}