code: def test_reservoir_size(self):
      self.reservoir = extensions.variable_statistics_plot.Reservoir(
          size=self.reservoir_size, data_shape=self.shape
      )
      for x in self.xs:
          self.reservoir.add(x)
      idxs, data = self.reservoir.get_data()
  
      assert len(idxs) == self.reservoir_size
      assert len(data) == self.reservoir_size
      assert idxs.ndim == 1
      assert data[0].shape == self.xs[0].shape
      testing.assert_allclose(idxs, numpy.sort(idxs))
  
file_path: chainer/tests/chainer_tests/training_tests/extensions_tests/test_variable_statistics_plot.py
imports: import os
  import unittest
  import numpy
  import six
  import chainer
  from chainer import testing
  from chainer.training import extensions
label_desc: Use image node_id 2 for calling the TestReservoir obj's underlying member method code with example usage: obj.test_reservoir_size() without return types