With the newest version (3.15.0) the below code fails with AttributeError: 'itertools._tee' object has no attribute 'start'

foo.py

class Client: def start(self): pass class Lock: def create_client(self): return Client() def start(self): self._client = self.create_client() self._client.start() 

test_foo.py

import foo def test(mocker): mocker.patch("foo.Client") lock = foo.Lock() mocker.spy(lock, "create_client") lock.start()

The problem ist, that spy checks if the returned instance is an iterator, but each MagicMock is an iterator which leads to issues.
The logic should exclude any mock object IMO which should solve the issue