code: def check_multiple_output_1arg(self, xp, skip_retain_grad_test=False):
      x = chainer.Variable(xp.array([1, 2], np.float32))
      h = x * 2
      y0 = h * 3
      y1 = h * 4
      y0.grad = xp.array([1, 10], np.float32)
      y1.grad = xp.array([100, 1000], np.float32)
      chainer.backward([y0, y1])
      testing.assert_allclose(x.grad, np.array([806, 8060], np.float32))
      if skip_retain_grad_test:
          return
      assert y0.grad is None
      assert y1.grad is None
  
imports: import unittest
  import mock
  import numpy
  import pytest
  import chainer
  from chainer.backends import cuda
  from chainer import testing
  from chainer.testing import attr
  import chainerx
label_desc: Use image node_id 2 for calling the TestBackward obj's underlying member method code with example usage: obj.check_multiple_output_1arg(xp, skip_retain_grad_test) without return types