code: def test_backcompat_prefix_works(self, uri):
      with patch.dict(in_dict=os.environ, AIRFLOW_CONN_MY_CONN=uri):
          hook = SlackWebhookHook(slack_webhook_conn_id="my_conn")
          params = hook._get_conn_params()
          assert params["url"] == "https://hooks.slack.com/services/abc"
          assert params["timeout"] == 123
          assert params["proxy"] == "proxy"
  
imports: from __future__ import annotations
  import json
  import os
  from typing import Any
  from unittest import mock
  from unittest.mock import patch
  import pytest
  from slack_sdk.http_retry.builtin_handlers import ConnectionErrorRetryHandler, RateLimitErrorRetryHandler
  from slack_sdk.webhook.webhook_response import WebhookResponse
  from airflow.exceptions import AirflowException, AirflowNotFoundException
  from airflow.models.connection import Connection
  from airflow.providers.slack.hooks.slack_webhook import SlackWebhookHook, check_webhook_response
label_desc: Use image node_id 13 for calling the TestSlackWebhookHook obj's underlying member method code with example usage: obj.test_backcompat_prefix_works(uri) without return types