如何使用flask-sqlalchemy编写doctest？

pip install Flask SQLAlchemy

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///test.db'
db = SQLAlchemy(app)

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique=True, nullable=False)
    email = db.Column(db.String(120), unique=True, nullable=False)

    def __repr__(self):
        return '<User %r>' % self.username

flask db init
flask db migrate
flask db upgrade

class User(db.Model):
    """
    A class representing a user.

    >>> user = User(username='john', email='john@example.com')
    >>> db.session.add(user)
    >>> db.session.commit()
    >>> user.id
    1
    >>> user.username
    'john'
    >>> user.email
    'john@example.com'
    """
    # ...

python -m doctest -v your_module.py