unittest.mock으로 모킹하기

모의 객체를 사용하는 이유

from unittest.mock import Mock

api = Mock()
api.get_user.return_value = {"id": 1, "name": "Alice"}

result = api.get_user(1)
print(result)  # {'id': 1, 'name': 'Alice'}

Mock과 MagicMock

from unittest.mock import MagicMock

m = MagicMock()
m.__len__.return_value = 5
print(len(m))  # 5

m.__iter__.return_value = iter([1, 2, 3])
for x in m:
    print(x)

데코레이터로 사용하는 patch

from unittest.mock import patch

def get_data():
    import requests
    return requests.get("https://api.example.com").json()

@patch("requests.get")
def test_get_data(mock_get):
    mock_get.return_value.json.return_value = {"key": "value"}
    result = get_data()
    assert result == {"key": "value"}

컨텍스트 관리자로 사용하는 patch

from unittest.mock import patch

def test_open():
    with patch("builtins.open", create=True) as mock_open:
        mock_open.return_value.__enter__.return_value.read.return_value = "data"
        with open("file.txt") as f:
            assert f.read() == "data"

patch.object

from unittest.mock import patch
import mymodule

def test_method():
    with patch.object(mymodule.MyClass, "fetch", return_value=42):
        obj = mymodule.MyClass()
        assert obj.fetch() == 42

호출 검증

from unittest.mock import Mock

send = Mock()
send("hello", to="alice")

send.assert_called_once_with("hello", to="alice")
print(send.call_count)  # 1

return_value와 side_effect

from unittest.mock import Mock

m = Mock(side_effect=[1, 2, ValueError("done")])
print(m())  # 1
print(m())  # 2
m()         # raises ValueError

spec: 형식이 안전한 모의 객체

from unittest.mock import Mock

class Calc:
    def add(self, a, b): return a + b

m = Mock(spec=Calc)
m.add(1, 2)         # OK
# m.subtract(1, 2)  # AttributeError: Mock does not have 'subtract'

patch.dict

from unittest.mock import patch
import os

def test_env():
    with patch.dict(os.environ, {"DEBUG": "true"}):
        assert os.environ["DEBUG"] == "true"
    assert "DEBUG" not in os.environ

pytest에서 pytest-mock으로 모의 객체 사용

# pip install pytest-mock

def test_service(mocker):
    mocker.patch("mymodule.requests.get", return_value=mocker.Mock(
        json=lambda: {"status": "ok"}
    ))
    from mymodule import call_api
    assert call_api()["status"] == "ok"

코루틴에 사용하는 AsyncMock

from unittest.mock import AsyncMock, patch
import asyncio

async def fetch():
    import httpx
    async with httpx.AsyncClient() as c:
        r = await c.get("https://example.com")
        return r.json()

def test_fetch():
    with patch("httpx.AsyncClient.get", new_callable=AsyncMock) as m:
        m.return_value.json.return_value = {"ok": True}
        result = asyncio.run(fetch())
        assert result["ok"] is True

빠른 확인

복습