code: def test_istask():
      assert istask((inc, 1))
      assert not istask(1)
      assert not istask((1, 2))
      f = namedtuple("f", ["x", "y"])
      assert not istask(f(sum, 2))
  
imports: import pickle
  from collections import namedtuple
  import pytest
  from flash.core.serve.dag.task import flatten, get, get_dependencies, get_deps, istask, literal, preorder_traversal, quote, subs
  from flash.core.serve.dag.utils_test import add, inc
  from flash.core.utilities.imports import _TOPIC_SERVE_AVAILABLE
label_desc: Use image node_id 2 for calling a global function with example usage: test_istask() without return types