code: def check_statistics(self, x, y):
      x = chainer.Variable(x)
      self.link(x, finetune=True)
      mean = self.x.mean(axis=0)
      testing.assert_allclose(self.link.avg_mean, mean)
      unbiased_var = self.x.var(axis=0) * self.nx / (self.nx - 1)
      testing.assert_allclose(self.link.avg_var, unbiased_var)
  
      y = chainer.Variable(y)
      with chainer.using_config("train", False):
          self.link(y, finetune=True)
      testing.assert_allclose(self.link.avg_mean, mean)
      testing.assert_allclose(self.link.avg_var, unbiased_var)
  
imports: import unittest
  import numpy
  import six
  import chainer
  from chainer.backends import cuda
  from chainer import links
  from chainer import testing
  from chainer.testing import attr
label_desc: Use image node_id 2 for calling the TestPopulationStatistics obj's underlying member method code with example usage: obj.check_statistics(x, y) without return types