code: def test_trainer_reference_recursively():
      ensemble = LightningModule()
      inner = LightningModule()
      ensemble.inner = inner
  
      assert inner._trainer is None
      with pytest.raises(RuntimeError, match="attached to a `Trainer"):
          _ = ensemble.trainer
  
      trainer = Mock()
      ensemble.trainer = trainer
      # references match
      assert ensemble.trainer is inner.trainer
      if not _TORCH_GREATER_EQUAL_2_0:
          # and the trainer was weakly referenced
          assert inner.trainer is weakref.proxy(trainer)
  
imports: import sys
  import weakref
  from unittest.mock import Mock
  import pytest
  import torch
  from lightning.fabric import Fabric
  from lightning.fabric.utilities.imports import _TORCH_GREATER_EQUAL_1_13, _TORCH_GREATER_EQUAL_2_0
  from lightning.pytorch import LightningModule, Trainer
  from lightning.pytorch.core.module import _TrainerFabricShim
  from lightning.pytorch.demos.boring_classes import BoringModel
  from lightning.pytorch.loggers import TensorBoardLogger
  from lightning.pytorch.utilities.exceptions import MisconfigurationException
  from torch import nn
  from torch.optim import SGD, Adam
  from tests_pytorch.helpers.runif import RunIf
label_desc: Use image node_id 17 for calling a global function with example usage: test_trainer_reference_recursively() without return types