python - 如何正确运行查询 Flask-SQLAlchemy 数据库的连续测试？

Question

我正在使用 SQLAlchemy 作为 ORM 为 Flask 项目设置单元测试。对于我的测试，每次运行单个单元测试时，我都需要设置一个新的测试数据库。不知何故，我似乎无法运行查询数据库的连续测试，即使我单独运行这些测试它们也会成功。

我使用flask-testing包，并遵循他们的文档here 。

这是一个说明问题的工作示例:

app.py:

from flask import Flask


def create_app():
    app = Flask(__name__)
    return app


if __name__ == '__main__':
    app = create_app()
    app.run(port=8080)

数据库.py:

from flask_sqlalchemy import SQLAlchemy

db = SQLAlchemy()

models.py:

from database import db


class TestModel(db.Model):
    """Model for testing."""

    __tablename__ = 'test_models'
    id = db.Column(db.Integer,
                   primary_key=True
                   )

测试/__init__.py:

from flask_testing import TestCase

from app import create_app
from database import db


class BaseTestCase(TestCase):
    def create_app(self):
        app = create_app()
        app.config.update({
            'SQLALCHEMY_DATABASE_URI': 'sqlite:///:memory:',
            'SQLALCHEMY_TRACK_MODIFICATIONS': False,
            'TESTING': True
        })
        db.init_app(app)
        return app

    def setUp(self):
        db.create_all()

    def tearDown(self):
        db.session.remove()
        db.drop_all()

test/test_app.py:

from models import TestModel
from test import BaseTestCase
from database import db


test_model = TestModel()


class TestApp(BaseTestCase):
    """WebpageEnricherController integration test stubs"""

    def _add_to_db(self, record):
        db.session.add(record)
        db.session.commit()
        self.assertTrue(record in db.session)

    def test_first(self):
        """
        This test runs perfectly fine
        """
        self._add_to_db(test_model)
        result = db.session.query(TestModel).first()
        self.assertIsNotNone(result, 'Nothing in the database')

    def test_second(self):
        """
        This test runs fine in isolation, but fails if run consecutively
        after the first test
        """
        self._add_to_db(test_model)
        result = db.session.query(TestModel).first()
        self.assertIsNotNone(result, 'Nothing in the database')


if __name__ == '__main__':
    import unittest
    unittest.main()

因此，如果单独运行，我可以很好地运行 TestApp.test_first 和 TestApp.test_second 。如果我连续运行它们，第一个测试会通过，但第二个测试会失败:

=================================== FAILURES ===================================
_____________________________ TestApp.test_second ______________________________

self = <test.test_app.TestApp testMethod=test_second>

    def test_second(self):
        """
        This test runs fine in isolation, but fails if run consecutively
        after the first test
        """
        self._add_to_db(test_model)
        result = db.session.query(TestModel).first()
>       self.assertIsNotNone(result, 'Nothing in the database')
E       AssertionError: unexpectedly None : Nothing in the database

数据库设置和拆卸过程中出现问题，但我不知道是什么问题。我该如何正确设置？

Answer 1

答案是，通过重用在模块范围内定义的单个 TestModel 实例 (test_model = TestModel())，您会在一个测试和下一个测试之间泄漏状态.

第一次测试开始时该实例的状态是 transient :

an instance that’s not in a session, and is not saved to the database; i.e. it has no database identity. The only relationship such an object has to the ORM is that its class has a mapper() associated with it.

第二次测试开始时对象的状态是分离:

Detached - an instance which corresponds, or previously corresponded, to a record in the database, but is not currently in any session. The detached object will contain a database identity marker, however because it is not associated with a session, it is unknown whether or not this database identity actually exists in a target database. Detached objects are safe to use normally, except that they have no ability to load unloaded attributes or attributes that were previously marked as “expired”.

测试之间的这种相互依赖几乎总是一个坏主意。您可以使用 make_transient()在每次测试结束时的对象上:

class BaseTestCase(TestCase):
    ...
    def tearDown(self):
        db.session.remove()
        db.drop_all()
        make_transient(test_model)

或者您应该为每个测试构建一个新的 TestModel 实例:

class BaseTestCase(TestCase):
    ...
    def setUp(self):
        db.create_all()
        self.test_model = TestModel()


class TestApp(BaseTestCase):
    ...
    def test_xxxxx(self):
        self._add_to_db(self.test_model)

我认为后者是更好的选择，因为在测试之间不存在任何其他泄漏状态的危险。