如何測試在 FastAPI 路由中使用了 model？

Question

我正在嘗試檢查特定的 model 是否用作 FastAPI 路由的輸入解析器。 但是，我不確定如何修補（或監視）它。

我有以下文件結構：

.
└── roo
    ├── __init__.py
    ├── main.py
    └── test_demo.py

主要.py：

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class ItemModel(BaseModel):
    name: str

@app.post("/")
async def read_main(item: ItemModel):
    return {"msg": f"Item: {item.name}"}

test_demo.py：

from fastapi.testclient import TestClient
from unittest.mock import patch
from roo.main import app, ItemModel

client = TestClient(app)

def test_can_creating_new_item_users_proper_validation_model():
    with patch('roo.main.ItemModel', wraps=ItemModel) as patched_model:
        response = client.post("/", json={'name': 'good'})
    assert response.status_code == 200
    assert response.json() == {"msg": "Item: good"}
    assert patched_model.called

但是，從不調用patched_model （其他斷言通過）。 我不想更改功能或替換ItemModel中的 ItemModel，我只想檢查它是否被使用。

Answer 1

我的第一個方法是包裝read_main方法並檢查傳遞給 function 的item確實是ItemModel的一個實例。 但這是一個死胡同，因為 FastAPI 端點的准備和存儲方式：FastAPI 將端點 function 對象的副本存儲在一個列表中：（參見fastapi/routing.py ），然后在請求時評估哪個端點稱呼。

from roo.main import app

def test_read_main():
    assert 'read_main' in [r.endpoint.__name__ for r in app.routes]

    # check that read_main was called *and* received an ItemModel instance?

我的第二種方法涉及監視或“破壞” ItemModel的初始化，這樣如果端點確實使用了該 model，那么“損壞的” ItemModel將導致到達該端點的請求失敗。 我們利用以下事實“破壞” ItemModel ：（1）FastAPI 在請求-響應周期中調用 model 的__init__ ，以及（2）當端點無法序列化 model 時，默認傳播 422 錯誤響應適當地：

class ItemModel(BaseModel):
    name: str

    def __init__(__pydantic_self__, **data: Any) -> None:
        print("Make a POST request and confirm that this is printed out")
        super().__init__(**data)

所以在測試中，只需模擬__init__方法：

• pytest 示例

  import pytest from fastapi.testclient import TestClient from roo.main import app, ItemModel def test_read_main(monkeypatch: pytest.MonkeyPatch): client = TestClient(app) def broken_init(self, **data): pass # `name` and other fields won't be set monkeypatch.setattr(ItemModel, '__init__', broken_init) with pytest.raises(AttributeError) as exc: client.post("/", json={'name': 'good'}) assert 422 == response.status_code assert "'ItemModel' object has no attribute" in str(exc.value)

• pytest + pytest-mock的mocker.spy

   from fastapi.testclient import TestClient from pytest_mock import MockerFixture from roo.main import app, ItemModel def test_read_main(mocker: MockerFixture): client = TestClient(app) spy = mocker.spy(ItemModel, '__init__') client.post("/", json={'name': 'good'}) spy.assert_called() spy.assert_called_with(**{'name': 'good'})

• 單元測試示例

  from fastapi.testclient import TestClient from roo.main import app, ItemModel from unittest.mock import patch def test_read_main(): client = TestClient(app) # Wrapping __init__ like this isn't really correct, but serves the purpose with patch.object(ItemModel, '__init__', wraps=ItemModel.__init__) as mocked_init: response = client.post("/", json={'name': 'good'}) assert 422 == response.status_code mocked_init.assert_called() mocked_init.assert_called_with(**{'name': 'good'})

同樣，測試檢查端點是否在序列化為ItemModel或訪問item.name時失敗，這只會在端點確實使用ItemModel 。

如果您將端點從item: ItemModel修改為item: OtherModel ：

class OtherModel(BaseModel):
    name: str

class ItemModel(BaseModel):
    name: str

@app.post("/")
async def read_main(item: OtherModel):  # <----
    return {"msg": f"Item: {item.name}"}

那么現在運行測試應該會失敗，因為端點現在正在創建錯誤的 object：

    def test_read_main(mocker: MockerFixture):
        client = TestClient(app)
        spy = mocker.spy(ItemModel, '__init__')
    
        client.post("/", json={'name': 'good'})
>       spy.assert_called()
E       AssertionError: Expected '__init__' to have been called.

test_demo_spy.py:11: AssertionError

        with pytest.raises(AttributeError) as exc:
            response = client.post("/", json={'name': 'good'})
>           assert 422 == response.status_code
E           assert 422 == 200
E             +422
E             -200

test_demo_pytest.py:15: AssertionError

422 == 200 的斷言錯誤有點令人困惑，但這基本上意味着即使我們“破壞”了ItemModel ，我們仍然得到 200/OK 響應......這意味着ItemModel沒有被使用。

同樣，如果您先修改測試並模擬出OtherModel的__init__而不是ItemModel ，那么在不修改端點的情況下運行測試將導致類似的失敗測試：

    def test_read_main(mocker: MockerFixture):
        client = TestClient(app)
        spy = mocker.spy(OtherModel, '__init__')
    
        client.post("/", json={'name': 'good'})
>       spy.assert_called()
E       AssertionError: Expected '__init__' to have been called.

    def test_read_main():
        client = TestClient(app)
    
        with patch.object(OtherModel, '__init__', wraps=OtherModel.__init__) as mocked_init:
            response = client.post("/", json={'name': 'good'})
            # assert 422 == response.status_code
    
>           mocked_init.assert_called()
E           AssertionError: Expected '__init__' to have been called.

這里的斷言不那么令人困惑，因為它說我們期望端點會調用OtherModel的__init__ ，但它沒有被調用。 它應該在修改端點以使用item: OtherModel后通過。

最后要注意的一件事是，由於我們正在操縱__init__ ，因此它可能導致“快樂路徑”失敗，因此現在應該單獨對其進行測試。 確保撤消/還原模擬和補丁：

• pytest 示例

  def test_read_main(monkeypatch: pytest.MonkeyPatch): client = TestClient(app) def broken_init(self, **data): pass # Are we really using ItemModel? monkeypatch.setattr(ItemModel, '__init__', broken_init) with pytest.raises(AttributeError) as exc: response = client.post("/", json={'name': 'good'}) assert 422 == response.status_code assert "'ItemModel' object has no attribute" in str(exc.value) # Okay, really using ItemModel. Does it work correctly? monkeypatch.undo() response = client.post("/", json={'name': 'good'}) assert response.status_code == 200 assert response.json() == {"msg": "Item: good"}

• pytest + pytest-mock的mocker.spy

   from pytest_mock import MockerFixture from fastapi.testclient import TestClient from roo.main import app, ItemModel def test_read_main(mocker: MockerFixture): client = TestClient(app) # Are we really using ItemModel? spy = mocker.spy(ItemModel, '__init__') client.post("/", json={'name': 'good'}) spy.assert_called() spy.assert_called_with(**{'name': 'good'}) # Okay, really using ItemModel. Does it work correctly? mocker.stopall() response = client.post("/", json={'name': 'good'}) assert response.status_code == 200 assert response.json() == {"msg": "Item: good"}

• 單元測試示例

  def test_read_main(): client = TestClient(app) # Are we really using ItemModel? with patch.object(ItemModel, '__init__', wraps=ItemModel.__init__) as mocked_init: response = client.post("/", json={'name': 'good'}) assert 422 == response.status_code mocked_init.assert_called() mocked_init.assert_called_with(**{'name': 'good'}) # Okay, really using ItemModel. Does it work correctly? response = client.post("/", json={'name': 'good'}) assert response.status_code == 200 assert response.json() == {"msg": "Item: good"}

總而言之，您可能需要考慮是否/為什么檢查確切使用的 model 是否有用。 通常，我只檢查傳入的有效請求參數是否返回預期的有效響應，同樣，無效請求是否返回錯誤響應。