Python pytest SQLAlchemy会话中的完整性错误

我正在将烧瓶应用程序的测试从unittest移植到pytest。对于需要数据库的测试，我添加了一个返回DB会话的fixture

DB是一个运行PostgreSQL数据库的SQLAlchemy对象

import pytest
from app import create_app, db
from app.models import Project, Client

@pytest.fixture(scope='function')
def db_session():
    app = create_app('testing')

    app_context = app.app_context()
    app_context.push()

    db.create_all()

    yield db.session

    db.session.remove()
    db.drop_all()
    app_context.pop()

def test_getJson_withOneProjectSet_returnsBasicClientJson(db_session):
    testClient = Client()
    db_session.add(testClient)

    testProject = Project()
    db_session.add(testProject)

    testClient.projects.append(testProject)

    db_session.commit()

    clientJson = testClient.getJson()

    assert len(clientJson['projects']) == 1


def test_getJson_withThreeProjectsSet_returnsBasicClientJson(db_session):
    testClient = Client()
    db_session.add(testClient)

    testProject1 = Project()
    db_session.add(testProject1)

    testProject2 = Project()
    db_session.add(testProject2)

    testProject3 = Project()
    db_session.add(testProject3)

    testClient.projects.append(testProject1)
    testClient.projects.append(testProject2)
    testClient.projects.append(testProject3)

    db_session.commit()

    clientJson = testClient.getJson()

    assert len(clientJson['projects']) == 3

运行测试时，第一个测试通过，但第二个测试返回完整性错误：

sqlalchemy.exc.IntegrityError:（psycopg2.IntegrityError）重复键值违反唯一约束“project\u code\u key”

显然，在完成测试功能后，数据库没有被清理

夹具是来自工作unittest设置/拆卸功能的端口，该功能没有完整性错误问题：

# def setUp(self):
#     self.app = create_app('testing')
#     self.app_context = self.app.app_context()
#     self.app_context.push()
#     db.create_all()
#
# def tearDown(self):
#     db.session.remove()
#     db.drop_all()
#     self.app_context.pop()

尝试放置scope=“module”而不是函数，scope module意味着在所有测试中使用此db，然后将其删除