code: def test_core():
      a = Batch()
      b = a.pluck("x").map(inc)
      c = b.sum()
      L = c.stream.sink_to_list()
  
      a.emit([{"x": i, "y": 0} for i in range(4)])
  
      assert isinstance(b, Batch)
      assert isinstance(c, Streaming)
      assert L == [1 + 2 + 3 + 4]
  
imports: import pytest
  import toolz
  from streamz.batch import Batch, Streaming
  from streamz.utils_test import inc
label_desc: Use image node_id 1 for calling a global function with example usage: test_core() without return types