code: def _create_auto_validation_set(self, is_small=False):
      model = tc.activity_classifier.create(
          self.data,
          features=self.features,
          target=self.target,
          session_id=self.session_id,
          prediction_window=self.prediction_window,
          validation_set="auto",
      )
      predictions = model.predict(self.data)
  
      # Check the size of the auto validation set
      num_sessions = len(self.data[self.session_id].unique())
      valid_num_sessions = num_sessions - model.num_sessions
      valid_frac = float(valid_num_sessions / num_sessions)
      expected_frac = (
          0.0
          if is_small
          else 1.0 - self._compute_expect_frac(num_sessions)
      )
      self.assertAlmostEqual(
          valid_frac,
          expected_frac,
          places=1,
          msg="Got {} validation sessions out of {}, which is {:.3f}, and not the expected {}".format(
              valid_num_sessions,
              num_sessions,
              valid_frac,
              expected_frac,
          ),
      )
  
imports: from __future__ import print_function
  from __future__ import division
  from __future__ import absolute_import
  import unittest
  import turicreate
  import random
  import tempfile
  import math
  import numpy
  from numbers import Number
  from .None import util
  import pytest
  from turicreate.toolkits._internal_utils import _mac_ver
  from turicreate.toolkits._main import ToolkitError
  import uuid
label_desc: Use image node_id 3 for calling the ActivityClassifierAutoValdSetTest obj's underlying member method code with example usage: obj._create_auto_validation_set(is_small) without return types