python - FastAPI - 模拟路径功能没有效果

Question

我有一个简单的 FastAPI应用程序，我正在尝试使用 pytest 创建测试为了它。

我的目标是测试应用程序在出现不同错误时的行为。

我的应用中有一个简单的健康检查路线:

from fastapi import APIRouter

router = APIRouter()


@router.get("/health")
async def health():
    return "It's working ✨"

现在在我的 pytest 模块中，我试图修补上面的函数，以便它引发不同的错误。
我正在使用 unittest.mock但我的行为很奇怪。

import pytest
from unittest import mock

from fastapi import HTTPException
from starlette.testclient import TestClient

import app.api.health
from app.main import app  # this is my application (FastAPI instance) with the `router` attached


@pytest.fixture()
def client():
    with TestClient(app) as test_client:
        yield test_client


def test_simple(client):
    def mock_health_function():
        raise HTTPException(status_code=400, detail='gibberish')

    with mock.patch('app.api.health.health', mock_health_function):
        response = client.get(HEALTHCHECK_PATH)

        with pytest.raises(HTTPException):  # this check passes successfully - my exception is raised
            app.api.health.health()

    assert response.status_code != 200  # this check does not pass. The original function was called as if nothing was patched

尽管在测试内部调用了完全相同的函数，但 API 测试客户端在我到达端点时仍然调用原始函数。

为什么 mock.patch在测试中未直接调用函数时无法正常工作？

或者我应该以不同的方式解决我的问题？

Answer 1

您可以使用 monkeypatch fixture 来修补您的功能。
先把要打补丁的代码部分拉出来:

from fastapi import FastAPI

app = FastAPI()


def response():
    return "It's working ✨"


@app.get("/health")
async def health():
    return response()

然后在你的测试中使用monkeypatch

import pytest

from fastapi import HTTPException
from starlette.testclient import TestClient

from app import main


def mocked_response():
    raise HTTPException(status_code=400, detail='gibberish')


@pytest.fixture()
def client():
    from app.main import app

    with TestClient(app) as test_client:
        yield test_client


def test_simple(client, monkeypatch):

    monkeypatch.setattr(main, "response", mocked_response)
    resp = client.get("/health")
    assert resp.status_code == 400
    assert resp.json()["detail"] == "gibberish"

另一种方法是使用 Dependencies , 连同 dependencies_overrides .
这可能不适用于所有场景，但对于您给定的用例来说确实如此。

from fastapi import FastAPI,  Depends

app = FastAPI()


def response():
    return "It's working ✨"


@app.get("/health")
async def health(resp=Depends(response)):
    return resp

在您的测试客户端中，您现在可以像这样覆盖依赖项:

import pytest

from fastapi import HTTPException
from starlette.testclient import TestClient

from app.main import response


def mocked_response():
    raise HTTPException(status_code=400, detail='gibberish')


@pytest.fixture()
def client():
    from app.main import app
    app.dependency_overrides[response] = mocked_response

    with TestClient(app) as test_client:
        yield test_client


def test_simple(client):

    resp = client.get("/health")

    assert resp.status_code == 400
    assert resp.json()["detail"] == "gibberish"

如果您需要向响应函数添加参数，您可以使用闭包模式

def response_closure():
    def response(arg):
        return arg
    return response


@app.get("/health")
async def health(resp=Depends(response_closure)):
    return resp("It's working ✨")