code: def test_identity(self, backend_config):
      (x,) = self.generate_inputs()
      x = chainer.Variable(backend_config.get_array(x))
      y = functions.matmul(x, functions.inv(x))
      testing.assert_allclose(
          y.data, _make_eye(x.shape), **self.check_forward_options
      )
  
imports: import unittest
  import numpy
  import chainer
  from chainer.backends import cuda
  from chainer import functions
  from chainer import testing
  from chainer.testing import attr
  from chainer.utils import type_check
label_desc: Use image node_id 5 for calling the InvFunctionTest obj's underlying member method code with example usage: obj.test_identity(backend_config) without return types