我正在尝试monkeypatch外部请求。下面是一个Web端点的代码：

import httpx, json
...
@app.get('/test')
async def view_test(request):
    async with httpx.AsyncClient() as client:
# sending external request
        api_response = await client.get(
            f'https://jsonplaceholder.typicode.com/todos/1',
            timeout=10,
        )
        resp = api_response.json()
# modifying the result
        resp['foo'] = 0
# forwarding the modified result back to the user
        return HTTPResponse(json.dumps(resp), 200)

当用户向/test发送GET请求时，它会请求一个外部API（JSONPlaceholder），获取JSON结果并将'foo' = 0添加到其中。然后，它会将结果转发回用户。下面是Postman结果：

{
    "userId": 1,
    "id": 1,
    "title": "delectus aut autem",
    "completed": false,
    "foo": 0
}

下面是我的pytest代码：

import httpx, pytest
...
# The `client` parameter is the fixture of web app
def test_view_test(client, monkeypatch):
    async def return_mock_response(*args, **kwargs):
        return httpx.Response(200, content=b'{"response": "response"}')

    monkeypatch.setattr(httpx.AsyncClient, 'get', return_mock_response)
    _, response = client.test_client.get('/test')
    assert response.json == {'response': 'response', 'foo': 0}
    assert response.status_code == 200

我使用pytest的monkeypatch fixture来模拟HTTPX请求的结果{"response": "response"}，所以基本上我所期望的是端点将'foo' = 0添加到模拟结果中，但是它返回的是未修改的{"response": "response"}，下面是pytest -vv命令的回溯：

>       assert response.json == {'response': 'response', 'foo': 0}
E       AssertionError: assert {'response': 'response'} == {'response': 'response', 'foo': 0}
E         Common items:
E         {'response': 'response'}
E         Right contains 1 more item:
E         {'foo': 0}
E         Full diff:
E         - {'foo': 0, 'response': 'response'}
E         ?  ----------
E         + {'response': 'response'}

有人能帮我解释为什么端点不修改httpx.AsyncClient().get模拟结果吗？我使用sanic==22.9.0作为后端，httpx==0.23.0作为请求，pytest==7.2.0作为测试。
预期获得{'response': 'response', 'foo': 0}，而不是获得{"response": "response"}-模拟的httpx响应的未修改结果。