code: def test_default_engine(app: Flask, db: SQLAlchemy) -> None:
      with app.app_context():
          assert db.engine is db.engines[None]
  
      with pytest.raises(RuntimeError):
          assert db.engine
  
imports: from __future__ import annotations
  import os.path
  import typing
  import unittest.mock
  import pytest
  import sqlalchemy
  import sqlalchemy.pool
  from flask import Flask
  from flask_sqlalchemy import SQLAlchemy
label_desc: Use image node_id 1 for calling a global function with example usage: test_default_engine(app, db) without return types