code: def test_custom_tile_subdomains():
      """Test custom tile subdomains."""
      url = "http://{s}.custom_tiles.org/{z}/{x}/{y}.png"
      m = folium.Map()
      folium.TileLayer(
          tiles=url,
          name="subdomains2",
          attr="attribution",
          subdomains="mytilesubdomain",
      ).add_to(m)
      out = m._parent.render()
      assert "mytilesubdomain" in out
  
file_path: folium/tests/test_raster_layers.py
imports: import pytest
  import xyzservices
  from jinja2 import Template
  import folium
  from folium.utilities import normalize
label_desc: Use image node_id 3 for calling a global function with example usage: test_custom_tile_subdomains() without return types