code: def test_default_markers(self):
      # check overridden default for points
      m = self.cities.explore()
      strings = [
          '"radius":2',
          '"fill":true',
          "CircleMarker(latlng,opts)",
      ]
      out_str = self._fetch_map_string(m)
      for s in strings:
          assert s in out_str
  
      m = self.cities.explore(marker_kwds={"radius": 5, "fill": False})
      strings = [
          '"radius":5',
          '"fill":false',
          "CircleMarker(latlng,opts)",
      ]
      out_str = self._fetch_map_string(m)
      for s in strings:
          assert s in out_str
  
imports: import geopandas
  import numpy
  import pandas
  import pytest
  import shapely
  from packaging.version import Version
  from matplotlib import cm
  from matplotlib import colors
  from branca.colormap import StepColormap
label_desc: Use image node_id 18 for calling the TestExplore obj's underlying member method code with example usage: obj.test_default_markers() without return types