code: def test_astype(self):
      pser = self.pser
      psser = self.psser
  
      self.assert_eq(
          pser.astype(str).tolist(), psser.astype(str).tolist()
      )
  
      self.assert_eq(pser.astype("category"), psser.astype("category"))
      cat_type = CategoricalDtype(categories=["x", "y"])
      self.assert_eq(pser.astype(cat_type), psser.astype(cat_type))
      for dtype in self.object_extension_dtypes:
          if dtype in ["string", StringDtype()]:
              self.check_extension(
                  pser.astype(dtype), psser.astype(dtype)
              )
  
imports: import unittest
  import numpy
  import pandas
  from pandas.api.types import CategoricalDtype
  from pyspark import pandas
  from pyspark.pandas.config import option_context
  from pyspark.testing.pandasutils import PandasOnSparkTestCase
  from pyspark.pandas.tests.data_type_ops.testing_utils import OpsTestBase
  from pyspark.pandas.typedef.typehints import extension_object_dtypes_available
label_desc: Use image node_id 9 for calling the StringExtensionOpsTest obj's underlying member method code with example usage: obj.test_astype() without return types