code: def test_hard_tanh_double_backward(seed, ctx, func_name):
      from nbla_test_utils import (
          backward_function_tester,
          cap_ignore_region,
      )
  
      rng = np.random.RandomState(seed)
      inputs = [
          cap_ignore_region(
              rng.randn(2, 3).astype(np.float32), (-0.9, 0.9)
          )
      ]
      backward_function_tester(
          rng,
          F.hard_tanh,
          inputs=inputs,
          func_args=[],
          func_kwargs={},
          atol_accum=1e-3,
          dstep=1e-3,
          ctx=ctx,
      )
  
file_path: nnabla/python/test/function/test_hard_tanh.py
imports: import pytest
  import numpy
  import nnabla.functions
  from nbla_test_utils import list_context
label_desc: Use image node_id 4 for calling a global function with example usage: test_hard_tanh_double_backward(seed, ctx, func_name) without return types