code: def test_ensure_input_node_singleton(shared_ray_instance):
      @ray.remote
      def f(input):
          return input
  
      @ray.remote
      def combine(a, b):
          return a + b
  
      with InputNode() as input_1:
          a = f.bind(input_1)
      with InputNode() as input_2:
          b = f.bind(input_2)
          dag = combine.bind(a, b)
  
      with pytest.raises(
          AssertionError,
          match="Each DAG should only have one unique InputNode",
      ):
          _ = ray.get(dag.execute(2))
  
file_path: ray/python/ray/dag/tests/test_input_node.py
imports: import pytest
  from ray.dag.dag_node import DAGNode
  from ray.dag.input_node import InputNode
  from typing import Any, TypeVar
  import ray
label_desc: Use image node_id 11 for calling a global function with example usage: test_ensure_input_node_singleton(shared_ray_instance) and returns: input, unknown