code: def test_groupby(self):
      df = SimpleDataFrameSubClass(DataFrame({"a": [1, 2, 3]}))
  
      for _, v in df.groupby("a"):
          assert type(v) is DataFrame
  
imports: import numpy
  import pytest
  import pandas
  from pandas import DataFrame, Index, MultiIndex, Series
  import pandas._testing
label_desc: Use image node_id 4 for calling the TestSubclassWithoutConstructor obj's underlying member method code with example usage: obj.test_groupby() without return types