code: def check_forward(self, xs_data):
      xs = [chainer.Variable(x) for x in xs_data]
      y = functions.stack(xs, axis=self.axis)
  
      if hasattr(numpy, "stack"):
          # run test only with numpy>=1.10
          expect = numpy.stack(self.xs, axis=self.axis)
          testing.assert_allclose(y.data, expect)
  
      y_data = backend.CpuDevice().send(y.data)
      self.assertEqual(y_data.shape[self.axis], 2)
      numpy.testing.assert_array_equal(
          y_data.take(0, axis=self.axis), self.xs[0]
      )
      numpy.testing.assert_array_equal(
          y_data.take(1, axis=self.axis), self.xs[1]
      )
  
imports: import unittest
  import numpy
  import chainer
  from chainer import backend
  from chainer.backends import cuda
  from chainer import functions
  from chainer import gradient_check
  from chainer import testing
  from chainer.testing import attr
  import chainerx
label_desc: Use image node_id 2 for calling the TestStack obj's underlying member method code with example usage: obj.check_forward(xs_data) without return types