code: def forward_expected(self, inputs):
      (x,) = inputs
      x1 = x.astype(self.check_forward_dtype, copy=False)
      return (_inv(x1).astype(self.dtype),)
  
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 4 for calling the BatchInvFunctionTest obj's underlying member method code with example usage: obj.forward_expected(inputs) and returns: _inv