#include <bits/stdc++.h>
using namespace std;
struct dot {
  int x, y;
} d[1050];
int ans[5050];
bool cmp(dot a, dot b) {
  if (a.x == b.x) return a.y < b.y;
  return a.x < b.x;
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int t;
  cin >> t;
  while (t--) {
    int n;
    int flag = 0, cnt = 0;
    cin >> n;
    for (int i = 0; i <= 1049; i++) d[i].x = 0, d[i].y = 0;
    memset(ans, 0, sizeof(ans));
    for (int i = 1; i <= n; i++) cin >> d[i].x >> d[i].y;
    sort(d + 1, d + 1 + n, cmp);
    int x, y, nx, ny;
    x = 0;
    y = 0;
    for (int i = 1; i <= n; i++) {
      nx = d[i].x;
      ny = d[i].y;
      if (ny < y || nx < x) {
        flag = 1;
        break;
      }
      for (int j = x; j < nx; j++) ans[++cnt] = 1;
      for (int j = y; j < ny; j++) ans[++cnt] = 2;
      x = nx;
      y = ny;
    }
    if (flag)
      cout << "NO" << endl;
    else {
      cout << "YES" << endl;
      for (int i = 1; i <= cnt; i++) {
        if (ans[i] == 1)
          cout << "R";
        else
          cout << "U";
      }
      cout << endl;
    }
  }
  return 0;
}
