code: def test_SPDN_sparse_matmul_backward_cpu(self):
      if not _scipy_available:
          return
      self.check_SPDN_backward(
          self.a, self.b, self.gc, atol=1e-2, rtol=1e-2
      )
  
imports: import unittest
  import numpy
  import chainer
  from chainer import cuda
  import chainer.functions
  from chainer import gradient_check
  from chainer import testing
  from chainer.testing import attr
  from chainer import utils
  from chainer.utils import type_check
label_desc: Use image node_id 8 for calling the TestCooMatMul obj's underlying member method code with example usage: obj.test_SPDN_sparse_matmul_backward_cpu() without return types