code: def test_phase_context_double_nested():
      graph_manager = GraphManager(
          name="",
          schedule_params=ScheduleParameters(),
          vis_params=VisualizationParameters(),
      )
  
      assert graph_manager.phase == RunPhase.UNDEFINED
      with graph_manager.phase_context(RunPhase.TRAIN):
          assert graph_manager.phase == RunPhase.TRAIN
          with graph_manager.phase_context(RunPhase.TEST):
              assert graph_manager.phase == RunPhase.TEST
              with graph_manager.phase_context(RunPhase.UNDEFINED):
                  assert graph_manager.phase == RunPhase.UNDEFINED
              assert graph_manager.phase == RunPhase.TEST
          assert graph_manager.phase == RunPhase.TRAIN
      assert graph_manager.phase == RunPhase.UNDEFINED
  
file_path: coach/rl_coach/tests/graph_managers/test_graph_manager.py
imports: import os
  import sys
  import pytest
  from rl_coach.graph_managers.graph_manager import GraphManager, ScheduleParameters
  from rl_coach.base_parameters import VisualizationParameters
  from rl_coach.core_types import RunPhase
label_desc: Use image node_id 3 for calling a global function with example usage: test_phase_context_double_nested() without return types