code: def mutation_start(self, mutator, model):
      self.iteration += 1
  
imports: import json
  from pathlib import Path
  import pytest
  from nni.common.framework import get_default_framework, set_default_framework
  from nni.nas.space import StationaryMutator, Mutator, MutationSampler, GraphModelSpace, ModelStatus, MutatorSequence
  from nni.nas.space.mutator import _RandomSampler
  from nni.nas.space.graph_op import Operation
label_desc: Use image node_id 3 for calling the DebugSampler obj's underlying member method code with example usage: obj.mutation_start(mutator, model) without return types