code: def test_tree_reduce_futures(n_parts, client):
      a = [client.submit(s, i) for i in range(n_parts)]
      b = tree_reduce(a)
      c = client.compute(b, sync=True)
  
      assert sum(range(n_parts)) == c
  
imports: from dask import delayed
  import pytest
  from cuml.dask.common.func import reduce
  from cuml.dask.common.func import tree_reduce
label_desc: Use image node_id 3 for calling a global function with example usage: test_tree_reduce_futures(n_parts, client) without return types