code: def test_add_n_double_backward(num_inputs, seed, ctx, func_name):
      from nbla_test_utils import backward_function_tester
  
      rng = np.random.RandomState(seed)
      shape0 = [2, 3, 4]
      inputs = []
      for i in range(num_inputs):
          inputs.append(rng.randn(*shape0).astype(np.float32))
      backward_function_tester(
          rng,
          F.add_n,
          inputs=inputs,
          func_args=[],
          func_kwargs={},
          atol_accum=5e-2,
          dstep=1e-3,
          ctx=ctx,
      )
  
file_path: nnabla/python/test/function/test_add_n.py
imports: import pytest
  import numpy
  import nnabla
  import nnabla.functions
  from nbla_test_utils import list_context
label_desc: Use image node_id 3 for calling a global function with example usage: test_add_n_double_backward(num_inputs, seed, ctx, func_name) without return types