code: def test_no_layers(self):
      match = r"One or more layers must be defined\."
      with pytest.raises(ValueError, match=match):
          ogc.WMSRasterSource(self.URI, [])
  
imports: from unittest import mock
  from xml.etree.ElementTree import ParseError
  import numpy
  import pytest
  import cartopy.crs
  from cartopy.tests.conftest import _HAS_PYKDTREE_OR_SCIPY
  import cartopy.io.ogc_clients
  from cartopy.io.ogc_clients import _OWSLIB_AVAILABLE
label_desc: Use image node_id 4 for calling the TestWMSRasterSource obj's underlying member method code with example usage: obj.test_no_layers() without return types