code: def test_signal_connector_in_thread():
      with concurrent.futures.ThreadPoolExecutor(
          max_workers=1
      ) as executor:
          for future in concurrent.futures.as_completed(
              [executor.submit(_registering_signals)]
          ):
              assert future.exception() is None
  
imports: import concurrent.futures
  import os
  import signal
  from unittest import mock
  from unittest.mock import Mock
  import pytest
  from lightning.fabric.plugins.environments import SLURMEnvironment
  from lightning.fabric.utilities.imports import _IS_WINDOWS
  from lightning.pytorch import Trainer
  from lightning.pytorch.demos.boring_classes import BoringModel
  from lightning.pytorch.trainer.connectors.signal_connector import _SignalConnector
  from lightning.pytorch.utilities.exceptions import SIGTERMException
  from tests_pytorch.helpers.runif import RunIf
label_desc: Use image node_id 8 for calling a global function with example usage: test_signal_connector_in_thread() without return types