code: def test_array_backward():
      with chainerx.backprop_scope("bp1") as bp1:
          x1 = chainerx.array([1, 1, 1], chainerx.float32).require_grad(
              backprop_id=bp1
          )
          x2 = chainerx.array([1, 1, 1], chainerx.float32).require_grad(
              backprop_id=bp1
          )
          y = x1 * x2
  
          y.backward(backprop_id=bp1, enable_double_backprop=True)
          gx1 = x1.get_grad(backprop_id=bp1)
          x1.set_grad(None, backprop_id=bp1)
  
          gx1.backward(backprop_id=bp1)
          with pytest.raises(chainerx.ChainerxError):
              gx1.get_grad(backprop_id=bp1)
  
imports: import copy
  import math
  import pickle
  import numpy
  import pytest
  import chainerx
  import chainerx.testing
  from chainerx_tests import array_utils
label_desc: Use image node_id 28 for calling a global function with example usage: test_array_backward() without return types