Python SQLAlchemy关系测试

Question

来自Rails世界中的测试，在rspec中有一种简单的方法可以测试模型关系是否正确设置：

require 'spec_helper'

RSpec.describe Country, type: :model do
  it {is_expected.to have_many :cities}

end

如何为使用SQL Alchemy在Flask应用程序中创建的这些模型编写关系测试？

class City(SurrogatePK, Model):
    """
    https://dev.mysql.com/doc/sakila/en/sakila-structure-tables-city.html
    city_id: A surrogate primary key used to uniquely identify each city in the table.
    city: The name of the city.
    country_id: A foreign key identifying the country that the city belongs to.
    last_update: The time that the row was created or most recently updated.
    """
    __tablename__ = 'cities'
    city = Column(db.String(50), nullable=False)
    country_id = reference_col('countries', nullable=True)
    country_id = db.Column(db.Integer, db.ForeignKey('countries.id'),nullable=False)
    last_update = Column(db.DateTime, nullable=False, default=dt.datetime.utcnow)
    country = db.relationship('Country', foreign_keys= [country_id], backref='cities', lazy=True)


    def __repr__(self):
        """Represent instance as a unique string."""
        return '<City ({city})>'.format(city=self.city)


class Country(SurrogatePK, Model):
    """
    https://dev.mysql.com/doc/sakila/en/sakila-structure-tables-country.html
    country_id: A surrogate primary key used to uniquely identify each country in the table.
    country: The name of the country.
    last_update: The time that the row was created or most recently updated.
    """
    __tablename__ = 'countries'
    country = Column(db.String(50), nullable=False)
    last_update = Column(db.DateTime, nullable=False, default=dt.datetime.utcnow)


    def __repr__(self):
        """Represent instance as a unique string."""
        return '<Country ({country})>'.format(country=self.country)

我的想法是，我只会创建一个城市，然后尝试将其添加到国家/地区。我想知道是否有更好的方法。