[Python] Closing a session in Flask, SQLAlchemy to delete the temporaryx file

I know there are similar questions out there, but none answered my problem.

I am using a basic test setup in Flask using SQLAlchemy, that is a slightly modified version of the Flask-tutorial tests. My problem is that the temporary file created by the app-fixture cannot be closed. This is the fixture:

import os
import tempfile

import pytest
from flask.testing import FlaskClient

# custom modules: create_app is the function factory, db is flask_sqlalchemy.SQLAlchemy(model_class=Base)
from flaskr import create_app
from flaskr.models import db

@pytest.fixture
def app():
# creates and opens a temporary file
db_fd, db_path = tempfile.mkstemp(dir="test")

# call the factory function, override DATABASE path so it points to the temporary
# path instead of the instance folder
app = create_app(
{
"TESTING": True,
"SQLALCHEMY_DATABASE_URI": f"sqlite:///{db_path}",
}
)

with app.test_client() as test_client:
with app.app_context():
db.create_all()

yield app

with app.test_client() as test_client:
with app.app_context():
db.drop_all()
db.session.remove()

os.close(db_fd)
os.unlink(db_path)


os.unlink() always fails, because the file is still used by another process. A typical usage in a test would be

def test_example(app):
with app.app_context():
assert db.session.execute(stmt) ...


I could probably just use the same file for testing the database every time, then delete it at the start of the app()-fixture, but I am worried that the cause of the unterminated session connection might also cause other problems, so I would like to understand and fix it.

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