code: def ref_unlink(x):
      return x
  
file_path: nnabla/python/test/function/test_unlink.py
imports: import pytest
  import numpy
  import nnabla
  import nnabla.functions
  from nbla_test_utils import list_context
  from nnabla.testing import assert_allclose
label_desc: Use image node_id 1 for calling a global function with example usage: ref_unlink(x) and returns: x