Failed example at test isolation

conftest.py

import secrets
from datetime import timedelta

import pytest
from fastapi import FastAPI
from fastapi.testclient import TestClient
from fastapp import settings, crud
from sqlalchemy import create_engine
from sqlalchemy.engine import Engine
from sqlalchemy.orm import Session, sessionmaker

# from fastapp.main import app
# Create a test database and override app
from fastapp.db.session import DBBase, get_db
from fastapp.models.user import UserModel
from fastapp.routers.utils.security import create_access_token
from fastapp.schemas.user import UserCreateSchema

engine = create_engine(
    settings.TEST_DATABASE_URI,
    pool_pre_ping=True,
    connect_args={"check_same_thread": False},
)
TestSessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
DBBase.metadata.create_all(engine)

def override_get_db():
    try:
        db = TestSessionLocal()
        yield db
    finally:
        db.close()


@pytest.yield_fixture
def db_session() -> Session:
    """Returns an sqlalchemy session, and after the test tears down everything properly."""
    connection = engine.connect()
    # begin the nested transaction
    transaction = connection.begin()
    # use the connection with the already started transaction
    session = Session(bind=connection)

    yield session

    session.close()
    # roll back the broader transaction
    transaction.rollback()
    # put back the connection to the connection pool
    connection.close()


@pytest.fixture
def app(db_session) -> FastAPI:
    from fastapp.main import get_application  # local import for testing purpose

    app = get_application()
    app.dependency_overrides[get_db] = override_get_db
    return app


@pytest.fixture
def client(app) -> TestClient:
    client = TestClient(app)
    yield client
    print("end client")