using_mock.py

class DB:
    def query(self, *args, **kwargs):
        print("DB: ", args, kwargs)
        return {"Data for real DB"}


class API:
    def __init__(self):
        self.db = DB()

    def call(self):
        return self.db.query("do this", "do that")


def test_0_real_call():
    api = API()
    assert {'Data for real DB'} == api.call()


def test_1_magic_mock():
    """
    magic mock would answer any call and property with a new MagicMock
    """
    from unittest.mock import MagicMock

    api = API()
    api.db = MagicMock()
    assert not {'Data for real DB'} == api.call()
    assert isinstance(api.call(), MagicMock)


def test_1_magic_mock_return_specific():
    """
    magic mock can answer specific answers if needed
    """
    from unittest.mock import MagicMock

    api = API()
    api.db = MagicMock()
    api.db.query.return_value = {"Data for real DB"}
    assert {'Data for real DB'} == api.call()
    assert not isinstance(api.call(), MagicMock)