code: def test_tail(stream):
      df = cudf.DataFrame({"x": [1, 2, 3], "y": [4, 5, 6]})
      sdf = DataFrame(example=df, stream=stream)
  
      L = sdf.tail(2).stream.gather().sink_to_list()
  
      sdf.emit(df)
      sdf.emit(df)
  
      assert_eq(L[0], df.tail(2))
      assert_eq(L[1], df.tail(2))
  
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 27 for calling a global function with example usage: test_tail(stream) without return types