pytest-flask example with SQLAlchemy

Hi, there
Could you include a SQLAlchemy example in the documentation? I'm using the following code but it doesn't work:

import pytest

from projeto import create_app, db as _db


@pytest.fixture(scope='session')
def app():
    app = create_app('testing')
    return app


@pytest.fixture(scope='session')
def db(app, request):
    _db.app = app
    _db.create_all()
    yield _db
    _db.drop_all()


@pytest.yield_fixture(scope='function')
def session(db):
    connection = db.engine.connect()
    transaction = connection.begin()

    options = dict(bind=connection)
    session = db.create_scoped_session(options=options)

    db.session = session

    yield session

    transaction.rollback()
    connection.close()
    session.remove()

This is the error that I get:

app = <Flask 'projeto'>, request = <SubRequest 'db' for <Function 'test_login_page'>>

    @pytest.fixture(scope='session')
    def db(app, request):
       _db.app = app
       _db.create_all()
       yield _db
 >       _db.drop_all()

conftest.py:14: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
/home/andref/.virtualenvs/projeto/lib/python3.5/site-packages/flask_sqlalchemy/__init__.py:1015: in drop_all
    self._execute_for_all_tables(app, bind, 'drop_all')
/home/andref/.virtualenvs/projeto/lib/python3.5/site-packages/flask_sqlalchemy/__init__.py:999: in _execute_for_all_tables
    op(bind=self.get_engine(app, bind), **extra)
/home/andref/.virtualenvs/projeto/lib/python3.5/site-packages/flask_sqlalchemy/__init__.py:941: in get_engine
    return connector.get_engine()
/home/andref/.virtualenvs/projeto/lib/python3.5/site-packages/flask_sqlalchemy/__init__.py:533: in get_engine
    uri = self.get_uri()
/home/andref/.virtualenvs/projeto/lib/python3.5/site-packages/flask_sqlalchemy/__init__.py:524: in get_uri
    return self._app.config['SQLALCHEMY_DATABASE_URI']
/home/andref/.virtualenvs/projeto/lib/python3.5/site-packages/werkzeug/local.py:347: in __getattr__
    return getattr(self._get_current_object(), name)
/home/andref/.virtualenvs/projeto/lib/python3.5/site-packages/werkzeug/local.py:306: in _get_current_object
    return self.__local()
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

    def _find_app():
        top = _app_ctx_stack.top
        if top is None:
>           raise RuntimeError(_app_ctx_err_msg)
E           RuntimeError: Working outside of application context.
E           
E           This typically means that you attempted to use functionality that needed
E           to interface with the current application object in a way.  To solve
E           this set up an application context with app.app_context().  See the
E           documentation for more information.

/home/andref/.virtualenvs/projeto/lib/python3.5/site-packages/flask/globals.py:51: RuntimeError