code: def test_copy_df(self):
      expected = DataFrame({"a": [1, 2, 3]})
      result = SimpleDataFrameSubClass(expected).copy()
  
      assert (
          type(result) is DataFrame
      )  # assert_frame_equal only checks isinstance(lhs, type(rhs))
      tm.assert_frame_equal(result, expected)
  
imports: import numpy
  import pytest
  import pandas
  from pandas import DataFrame, Index, MultiIndex, Series
  import pandas._testing
label_desc: Use image node_id 1 for calling the TestSubclassWithoutConstructor obj's underlying member method code with example usage: obj.test_copy_df() without return types