starlette: AssertionError with middleware and TemplateResponse

A slightly neater solution, which can be injected into any test which already has the client injected:

@pytest.fixture
def exclude_middleware():
    user_middleware = app.user_middleware.copy()
    app.user_middleware = []
    app.middleware_stack = app.build_middleware_stack()
    yield
    app.user_middleware = user_middleware
    app.middleware_stack = app.build_middleware_stack()

Keeping my fingers crossed that this problem gets fixed soon 😄

Huge thanks Fotis

I currently have a hacky workaround for this.

Subclass Jinja2Templates and modify it to not send the context, this means you can’t test against the template context, but at least doesn’t fail. Does anyone have a better workaround than this (e.g. doesn’t involve changing anything in the application code, still allows tests with context)?

from starlette.responses import Response
from starlette.templating import Jinja2Templates as _Jinja2Templates, _TemplateResponse


class TestableJinja2Templates(_Jinja2Templates):
    def TemplateResponse(
        self,
        name: str,
        context: dict,
        status_code: int = 200,
        headers: dict = None,
        media_type: str = None,
        background=None,
    ) -> _TemplateResponse:
        if "request" not in context:
            raise ValueError('context must include a "request" key')
        template = self.get_template(name)
        return CustomTemplateResponse(
            template,
            context,
            status_code=status_code,
            headers=headers,
            media_type=media_type,
            background=background,
        )


class CustomTemplateResponse(_TemplateResponse):
    async def __call__(self, scope, receive, send) -> None:
        # context sending removed
        await Response.__call__(self, scope, receive, send)

has there been any update on this issue @tomchristie ? In its current state it’s effectively erroring out on unit-tests on resources that return templated responses if a middleware is present.

I see the workaround used in https://github.com/atviriduomenys/spinta/pull/22 but I’d rather not override such an important piece

Here’s my hacky workaround to this for now in case it helps anyone:

@pytest.fixture
def client():
    return TestClient(app)


# TODO: I've had to create an app without middleware for testing due to the following bug
# https://github.com/encode/starlette/issues/472
@pytest.fixture
def client_without_middleware(request):
    def fin():
        app.user_middleware = user_middleware
        app.middleware_stack = app.build_middleware_stack()

    user_middleware = app.user_middleware.copy()
    app.user_middleware = []
    app.middleware_stack = app.build_middleware_stack()

    request.addfinalizer(fin)
    return TestClient(app)

I then inject client_without_middleware into tests which render Jinja2 templates.

Yeah, that’s why the issue was closed.

Are there any updates on this? It has been 3 years since this issue has been raised and the only solution to this date is to test apps without middleware. Surely this should be possible?

btw: I think in general more verbose asserts should be used, e.g. in this case:

assert message["type"] == "http.response.start", message

or

assert message["type"] == "http.response.start", message["type"]