code: def test_copy_expert(self):
      open_mock = mock.mock_open(read_data='{"some": "json"}')
      with mock.patch(
          "airflow.providers.postgres.hooks.postgres.open", open_mock
      ):
          statement = "SQL"
          filename = "filename"
  
          self.cur.fetchall.return_value = None
  
          assert self.db_hook.copy_expert(statement, filename) is None
  
          assert self.conn.close.call_count == 1
          assert self.cur.close.call_count == 1
          assert self.conn.commit.call_count == 1
          self.cur.copy_expert.assert_called_once_with(
              statement, open_mock.return_value
          )
          assert open_mock.call_args.args == (filename, "r+")
  
imports: from __future__ import annotations
  import json
  import os
  from unittest import mock
  import psycopg2.extras
  import pytest
  from airflow.models import Connection
  from airflow.providers.postgres.hooks.postgres import PostgresHook
  from airflow.utils.types import NOTSET
label_desc: Use image node_id 3 for calling the TestPostgresHook obj's underlying member method code with example usage: obj.test_copy_expert() without return types