code: def test_backprop(self, backend_config):
      x2_arr = numpy.array([2, 3], numpy.float32)
      gy1_arr = numpy.array([2, 4], numpy.float32)
      x2_arr, gy1_arr = backend_config.get_array((x2_arr, gy1_arr))
  
      x2 = chainer.Variable(x2_arr, requires_grad=True)
  
      # Forward
      (y1,) = self.call_func(backend_config, x2)
  
      assert isinstance(y1.array, backend_config.xp.ndarray)
  
      # Backward
      y1.grad = gy1_arr
      y1.backward()
  
      assert isinstance(x2.grad, backend_config.xp.ndarray)
  
imports: import unittest
  import numpy
  import chainer
  from chainer import testing
  import chainer.testing.backend
  import chainerx
label_desc: Use image node_id 4 for calling the TestFunctionInputNone obj's underlying member method code with example usage: obj.test_backprop(backend_config) without return types