code: def test_convert_dtypes_preserves_subclass_with_constructor(self):
      class SubclassedDataFrame(DataFrame):
          @property
          def _constructor(self):
              return SubclassedDataFrame
  
      df = SubclassedDataFrame({"a": [1, 2, 3]})
      result = df.convert_dtypes()
      assert isinstance(result, SubclassedDataFrame)
  
imports: import numpy
  import pytest
  import pandas
  from pandas import DataFrame, Index, MultiIndex, Series
  import pandas._testing
label_desc: Use image node_id 30 for calling the TestDataFrameSubclassing obj's underlying member method code with example usage: obj.test_convert_dtypes_preserves_subclass_with_constructor() and returns: SubclassedDataFrame