code: def test_astype_extension_dtypes(self):
      pdf = pd.DataFrame(
          {
              "a": [1, 2, None, 4],
              "b": [1, None, None, 4],
              "c": [1, 2, None, None],
              "d": [None, 2, None, 4],
          }
      )
      psdf = ps.from_pandas(pdf)
  
      astype = {"a": "Int8", "b": "Int16", "c": "Int32", "d": "Int64"}
  
      self.assert_eq(psdf.astype(astype), pdf.astype(astype))
  
imports: from datetime import datetime, timedelta
  import unittest
  import numpy
  import pandas
  from pyspark import pandas
  from pyspark.pandas.typedef.typehints import extension_dtypes_available, extension_float_dtypes_available, extension_object_dtypes_available
  from pyspark.pandas.utils import is_testing
  from pyspark.testing.pandasutils import ComparisonTestBase
  from pyspark.testing.sqlutils import SQLTestUtils
label_desc: Use image node_id 7 for calling the FrameConstructorMixin obj's underlying member method code with example usage: obj.test_astype_extension_dtypes() without return types