def db_url(request):
    """ Database URL used in sqlalchemy.create_engine

    Use ``--test-db-url`` pytest parameter or override this fixture
    in your test to provide your desired test database url.
    For valid urls see: http://docs.sqlalchemy.org/en/latest/core/engines.html
    Defaults to SQLite memory database.

    .. warning::

        Ensure you are providing test database url since
        data will be deleted for each test function
        and schema will be recreated on each test run.
    """
    return request.config.getoption('TEST_DB_URL')