[Python] How to patch a 3rd party lib in a unit test with FastAPI client

I have an app/main.py for FastAPI which does:

import qdrant_client as QdrantClient
...

qdrant_client = QdrantClient(url=...)
qdrant_client.create_collection(...)
...

app = FastAPI()
...

@app.get("/my_endpoint")
def handle_my_endpoint(query: str):
...
qdrant_client.query_points(...)


And I want to write a unit for /my_endpoint.

So I have in the unit test file:

from fastapi.testclient import TestClient
from app.main import app

class Test(unittest.TestCase):

@patch('app.main.QdrantClient', qdrant_client=MagicMock())
def test_my_endpoint(self, qdrant_client):
qdrant_client.create_collection.return_value = None
with TestClient(app) as client:
resp = client.get("/my_endpoint", params={...})
...


But it doesn't work, it insists on actually using the real client which tries to really call a Qdrant server, which fails... What am I missing to set up that patch correctly?

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