code: def test_identity(stream):
      df = cudf.DataFrame({"x": [1, 2, 3], "y": [4, 5, 6]})
      sdf = DataFrame(example=df, stream=stream)
      L = sdf.stream.gather().sink_to_list()
  
      sdf.emit(df)
  
      assert L[0] is df
      assert list(sdf.example.columns) == ["x", "y"]
  
      x = sdf.x
      assert isinstance(x, Series)
      L2 = x.stream.gather().sink_to_list()
      assert not L2
  
      sdf.emit(df)
      assert isinstance(L2[0], cudf.Series)
      assert_eq(L2[0], df.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 3 for calling a global function with example usage: test_identity(stream) without return types