code: def test_mul2_double_backward(inplace, seed, ctx, func_name):
      from nbla_test_utils import backward_function_tester
  
      rng = np.random.RandomState(seed)
      inputs = [
          rng.randn(2, 3).astype(np.float32),
          rng.randn(2, 3).astype(np.float32) * 2,
      ]
      backward_function_tester(
          rng,
          F.mul2,
          inputs=inputs,
          func_args=[inplace],
          func_kwargs={},
          atol_accum=1e-2,
          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 1 for calling a global function with example usage: test_mul2_double_backward(inplace, seed, ctx, func_name) without return types