code: def check_forward(self, s_data, i_data, x_data):
      xp = backend.get_array_module(s_data)
      s = chainer.Variable(s_data)
      i = chainer.Variable(i_data)
      x = chainer.Variable(x_data)
  
      t = thin_stack.thin_stack_set(s, i, x)
  
      testing.assert_allclose(
          t.array[xp.arange(len(i_data)), i_data], x_data
      )
  
      # Thin stack reuses the same ndarray.
      self.assertIs(s_data, t.array)
  
imports: import unittest
  import numpy
  import chainer
  from chainer import backend
  from chainer import cuda
  from chainer import testing
  from chainer.testing import attr
  import thin_stack
label_desc: Use image node_id 2 for calling the TestThinStackSet obj's underlying member method code with example usage: obj.check_forward(s_data, i_data, x_data) without return types