code: def test_stack_double_backward(
      seed, axis, num_inputs, ctx, func_name
  ):
      from nbla_test_utils import backward_function_tester
  
      rng = np.random.RandomState(seed)
      shape = [2, 3, 4]
      inputs = [
          rng.randn(*shape).astype(np.float32)
          for x in range(num_inputs)
      ]
      backward_function_tester(
          rng,
          F.stack,
          inputs=inputs,
          func_args=[],
          func_kwargs=dict(axis=axis),
          atol_accum=1e-3,
          dstep=1e-3,
          ctx=ctx,
      )
  
imports: import pytest
  import numpy
  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_stack_double_backward(seed, axis, num_inputs, ctx, func_name) without return types