code: def add(x, y):
      return x + y
  
file_path: ray/python/ray/util/dask/tests/test_dask_callback.py
imports: import dask
  import pytest
  import ray
  from ray.util.dask import ray_dask_get, RayDaskCallback
label_desc: Use image node_id 2 for calling a global function with example usage: add(x, y) and returns: unknown