How to mock an external API with pytest_mock

pytest_mock_api.py

class Api():
    
    def persons(self):
        return ['hek2mgl', 'lgm2keh']


class App(Api):
    
    def hello_messages(self):
        msg = [] 
        for p in self.persons():
            msg += ["Hello {}".format(p)]

        return msg


def test_app(mocker):
    mocker.patch('{}.Api.persons'.format(__name__),
        return_value=['a','b'])

    a = App()
    assert a.hello_messages() == ([ 
        "Hello a",
        "Hello b"
    ])