code: def test_get_prequeries() -> None:
      """
      Test the ``get_prequeries`` method.
      """
      from superset.db_engine_specs.postgres import PostgresEngineSpec
  
      assert PostgresEngineSpec.get_prequeries() == []
      assert PostgresEngineSpec.get_prequeries(schema="test") == [
          'set search_path = "test"'
      ]
  
file_path: superset/tests/unit_tests/db_engine_specs/test_postgres.py
imports: from datetime import datetime
  from typing import Any, Optional
  import pytest
  from pytest_mock import MockFixture
  from sqlalchemy import types
  from sqlalchemy.dialects.postgresql import DOUBLE_PRECISION, ENUM, JSON
  from sqlalchemy.engine.url import make_url
  from superset.exceptions import SupersetSecurityException
  from superset.utils.core import GenericDataType
  from tests.unit_tests.db_engine_specs.utils import assert_column_spec, assert_convert_dttm
  from tests.unit_tests.fixtures.common import dttm
label_desc: Use image node_id 4 for calling a global function with example usage: test_get_prequeries() without return types