code: def test_partition_selection_per_to_cross_partition(self):
      output = cross_partition_combiners._partition_metrics_private_partitions(
          0.25
      )
      self.assertFalse(output.public_partitions)
      self.assertEqual(output.num_dataset_partitions, 1)
      self.assertEqual(
          output.kept_partitions,
          metrics.MeanVariance(0.25, 0.25 * 0.75),
      )
  
imports: from absl.testing import absltest
  from absl.testing import parameterized
  import dataclasses
  import math
  from unittest import mock
  from unittest.mock import patch
  from analysis import metrics
  from analysis import cross_partition_combiners
  import pipeline_dp
label_desc: Use image node_id 3 for calling the PerPartitionToCrossPartitionMetrics obj's underlying member method code with example usage: obj.test_partition_selection_per_to_cross_partition() without return types