Properly mock datastore Query

Question

I am trying to mock the datastore Client interaction in Python.

Thus I patched Query:

from google.cloud.datastore import Client
from unittest.mock import patch


def foo():
    client = Client()
    try:
        ancestor = client.key("anc", "123")
        query = client.query(kind="child", ancestor=ancestor)
        for q in query.fetch(limit=1):
            assert False, "Successfully mocked everything"
    finally:
        client.close()

p = patch(
    "google.cloud.datastore.client.Query",
    spec=["__call__", "fetch"],
)
with p as mock_klass:
    mock_klass.fetch.return_value = [1, 2] # This line seems to have no effect?
    foo()
    mock_klass.fetch.assert_called_once()

When I however execute the code, assert_called_once fails.

I seem to be doing something wrong when mocking but cannot figure out how to get it working. Would greatly appreciate if someone could indicate how to get this to work.

Answer 1

Needed to replace mock_klass.fetch with mock_klass.return_value.fetch.