code: def test_user_agent_default(self):
      geocoder = self.make_geocoder(user_agent=None)
      assert geocoder.headers["User-Agent"] == "mocked_user_agent/0.0.0"
  
file_path: geopy/test/geocoders/nominatim.py
imports: import warnings
  from unittest.mock import patch
  import pytest
  import geopy.geocoders
  from geopy.exc import ConfigurationError
  from geopy.geocoders import Nominatim
  from geopy.point import Point
  from test.geocoders.util import BaseTestGeocoder
label_desc: Use image node_id 1 for calling the BaseTestNominatim obj's underlying member method code with example usage: obj.test_user_agent_default() without return types