Add WSGI tests for missing input and invalid content length

[DevilsAutumn]

Problem

The WSGI adapter has a few small branches that are important but not directly covered by tests yet.

Current tests cover normal request body reads, negative CONTENT_LENGTH, body limits, missing CONTENT_LENGTH, path decoding, event-loop calls, and response finalizers:

• current WSGI tests

But these two WSGI adapter paths are still easy to miss:

• missing wsgi.input returns an empty body: adapter code
• invalid non-numeric CONTENT_LENGTH is treated as invalid by the request safety layer before the body is read: adapter code

This is small test coverage work, but it protects compatibility behavior for WSGI deployments.

Proposed behavior

Add focused tests in tests/integration/test_wsgi_adapter.py:

• when wsgi.input is missing, a handler that reads the body should receive b"";
• when CONTENT_LENGTH is invalid, the response should be 400 Bad Request with Invalid Content-Length header, and the input stream should not be read.

Keep the tests narrow. No runtime behavior change is expected unless the tests reveal a bug.

Alternatives considered

We could leave this to broader adapter tests, but these branches are small and easy to assert directly.

API sketch

# No public API change.

Working on this?

Please wait until a maintainer marks the issue accepted. After that, comment before starting and make sure nobody else is assigned or already working on it.

[Aarohi1Agarwal]

Hi! I'd like to work on this issue if it's still available. I'll start working on it and submit a PR.