如何测试在 FastAPI 路由中使用了 model？

Question

我正在尝试检查特定的 model 是否用作 FastAPI 路由的输入解析器。 但是，我不确定如何修补（或监视）它。

我有以下文件结构：

.
└── 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，从不调用patched_model （其他断言通过）。 我不想更改功能或替换ItemModel中的 ItemModel，我只想检查它是否被使用。

Answer 1

我的第一个方法是包装read_main方法并检查传递给 function 的item确实是ItemModel的一个实例。 但这是一个死胡同，因为 FastAPI 端点的准备和存储方式：FastAPI 将端点 function 对象的副本存储在一个列表中：（参见fastapi/routing.py ），然后在请求时评估哪个端点称呼。

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?

我的第二种方法涉及监视或“破坏” ItemModel的初始化，这样如果端点确实使用了该 model，那么“损坏的” ItemModel将导致到达该端点的请求失败。 我们利用以下事实“破坏” ItemModel ：（1）FastAPI 在请求-响应周期中调用 model 的__init__ ，以及（2）当端点无法序列化 model 时，默认传播 422 错误响应适当地：

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)

所以在测试中，只需模拟__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'})

• 单元测试示例

  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'})

同样，测试检查端点是否在序列化为ItemModel或访问item.name时失败，这只会在端点确实使用ItemModel 。

如果您将端点从item: ItemModel修改为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}"}

那么现在运行测试应该会失败，因为端点现在正在创建错误的 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 的断言错误有点令人困惑，但这基本上意味着即使我们“破坏”了ItemModel ，我们仍然得到 200/OK 响应......这意味着ItemModel没有被使用。

同样，如果您先修改测试并模拟出OtherModel的__init__而不是ItemModel ，那么在不修改端点的情况下运行测试将导致类似的失败测试：

    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.

这里的断言不那么令人困惑，因为它说我们期望端点会调用OtherModel的__init__ ，但它没有被调用。 它应该在修改端点以使用item: OtherModel后通过。

最后要注意的一件事是，由于我们正在操纵__init__ ，因此它可能导致“快乐路径”失败，因此现在应该单独对其进行测试。 确保撤消/还原模拟和补丁：

• 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"}

• 单元测试示例

  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"}

总而言之，您可能需要考虑是否/为什么检查确切使用的 model 是否有用。 通常，我只检查传入的有效请求参数是否返回预期的有效响应，同样，无效请求是否返回错误响应。