code: def test_to_frame(stream):
      df = cudf.DataFrame({"x": [1, 2, 3], "y": [4, 5, 6]})
      sdf = DataFrame(example=df, stream=stream)
  
      assert sdf.to_frame() is sdf
  
      a = sdf.x.to_frame()
      assert isinstance(a, DataFrame)
      assert list(a.columns) == ["x"]
  
imports: import json
  import operator
  import numpy
  import pandas
  import pytest
  from dask.dataframe.utils import assert_eq
  from distributed import Client
  from streamz import Stream
  from streamz.dask import DaskStream
  from streamz.dataframe import Aggregation, DataFrame, DataFrames, Series
label_desc: Use image node_id 24 for calling a global function with example usage: test_to_frame(stream) without return types