code: def test_SingleDiagnosticBestModelSelector_max_mean(self) -> None:
      s = SingleDiagnosticBestModelSelector(
          diagnostic="Fisher exact test p",
          criterion=max,
          metric_aggregation=np.mean,
      )
      self.assertEqual(s.best_diagnostic(self.diagnostics), 2)
  
imports: from typing import List
  from unittest import mock
  import numpy
  from ax.core.metric import Metric
  from ax.core.objective import MultiObjective, Objective
  from ax.core.observation import Observation, ObservationData, ObservationFeatures
  from ax.core.optimization_config import MultiObjectiveOptimizationConfig, OptimizationConfig
  from ax.core.outcome_constraint import OutcomeConstraint
  from ax.core.types import ComparisonOp
  from ax.modelbridge.cross_validation import assess_model_fit, compute_diagnostics, cross_validate, cross_validate_by_trial, CVDiagnostics, CVResult, has_good_opt_config_model_fit, SingleDiagnosticBestModelSelector
  from ax.modelbridge.registry import Models
  from ax.utils.common.testutils import TestCase
  from ax.utils.testing.core_stubs import get_branin_experiment
label_desc: Use image node_id 11 for calling the CrossValidationTest obj's underlying member method code with example usage: obj.test_SingleDiagnosticBestModelSelector_max_mean() without return types