code: def test_both_channel_and_channels_set(self):
      error_message = (
          r"Cannot set both arguments: channel=.* and channels=.*\."
      )
      with pytest.raises(ValueError, match=error_message):
          SlackAPIFileOperator(
              task_id="slack",
              slack_conn_id=SLACK_API_TEST_CONNECTION_ID,
              channel="#random",
              channels="#general",
          )
  
imports: from __future__ import annotations
  import json
  from unittest import mock
  from unittest.mock import MagicMock
  import pytest
  from airflow.exceptions import AirflowProviderDeprecationWarning
  from airflow.providers.slack.operators.slack import SlackAPIFileOperator, SlackAPIOperator, SlackAPIPostOperator
label_desc: Use image node_id 7 for calling the TestSlackAPIFileOperator obj's underlying member method code with example usage: obj.test_both_channel_and_channels_set() without return types