starlette.TestClient with Jinja2Templates and middleware

[bloomingmath]

Describe the bug

The problem arise when using starlette TestClient to get a template response that passes through a middleware.

To Reproduce

I made a repo with the minimal fastapi app to raise the error:

https://github.com/bloomingmath/fastapi-middleware-issue

To reproduce, clone the repo and run pytest main.py

Expected behavior

I expect the test to run flawlessly, but it raise AssertionError as shown in the readme.md of the same repo.

Environment

• OS: Ubuntu 18.04
• Python 3.7.5
• attrs==19.3.0
• certifi==2019.11.28
• chardet==3.0.4
• fastapi==0.45.0
• idna==2.8
• importlib-metadata==1.3.0
• Jinja2==2.10.3
• MarkupSafe==1.1.1
• more-itertools==8.0.2
• packaging==19.2
• pluggy==0.13.1
• py==1.8.0
• pydantic==1.2
• pyparsing==2.4.5
• pytest==5.3.2
• requests==2.22.0
• six==1.13.0
• starlette==0.12.9
• urllib3==1.25.7
• wcwidth==0.1.7
• zipp==0.6.0

[podhmo]

This is related issue, in starlette, maybe...

encode/starlette#472

Hmm.. this is strange, maybe. Somehow, message["type"] is not "http.response.start", in starlette's middleware.
I print debugged, this value is "http.response.template".

actual value is like below.

{'type': 'http.response.template', 'template': <Template 'page.html'>, 'context': {'request': <starlette.requests.Request object at 0x7f9f2ced5850>}}

So, assertion error occured in this line

https://github.com/encode/starlette/blob/00e830080499c47a3e72f1b4adb2678758e388ee/starlette/middleware/base.py#L47

but async-asgi-testclient is ok

Writing similar tests, using async-asgi-testclient , test is passed.

import pytest


@pytest.mark.asyncio
async def test_middleware2():
    from async_asgi_testclient import TestClient

    async with TestClient(app) as client:
        response = await client.get("/")
        assert "X-Process-Time" in response.headers

then, message value is below

{'type': 'http.response.start', 'status': 200, 'headers': [(b'content-length', b'131'), (b'content-type', b'text/html; charset=utf-8')]}

[bloomingmath]

You are right @podhmo, the problem is with starlette and not with fastapi. Also, using async-asgi-testclient permits testing the application until starlette's test client is fixed.
Thank you for your help.

[podhmo]

OK. I understood completely. This is the same issue as encode/starlette#472

1. Starlette's template response class treats specially when scope has { "extensions": { "http.response.template": ...}}, then returns "http.response.template" message. ( here )
2. when Starlette's testclient sendindg http request, always attaching data including { "extensions": { "http.response.template": ...}} ( here )
3. And, BaseMiddleware asserting "http.response.start" message. ( here )

So, test is failed.

[tiangolo]

Thanks for the help here @podhmo ! 👏 🙇

Thanks for reporting back and closing the issue @bloomingmath 👍