starlette Test failure (Fix)

The Fix

Fix middleware traceback fetching on Python 3.8+, fix ResourceWarnings in TestClient, and fix CI build.

Based on closed Kludex/starlette issue #1131 · PR/commit linked

Jump to Verify Open PR/Commit

@@ -217,15 +217,15 @@ def generate_html(self, exc: Exception, limit: int = 7) -> str:
             exc, capture_locals=True
         )
-        frames = inspect.getinnerframes(
-            traceback_obj.exc_traceback, limit  # type: ignore
-        )

repro.py

============================= test session starts ==============================
platform linux -- Python 3.8.7, pytest-6.1.2, py-1.9.0, pluggy-0.13.1
rootdir: /build/source, configfile: setup.cfg
plugins: asyncio-0.14.0, cov-2.10.1
collected 240 items                                                            
[...]
=================================== FAILURES ===================================
_______________________________ test_debug_html ________________________________

    def test_debug_html():
        async def app(scope, receive, send):
            raise RuntimeError("Something went wrong")

        app = ServerErrorMiddleware(app, debug=True)
        client = TestClient(app, raise_server_exceptions=False)
        response = client.get("/", headers={"Accept": "text/html, */*"})
        assert response.status_code == 500
      assert response.headers["content-type"].startswith("text/html")

tests/middleware/test_errors.py:42:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = {}, key = 'content-type'

    def __getitem__(self, key):
      return self._store[key.lower()][1]
E       KeyError: 'content-type'

/nix/store/9bb3iygm8kkdzfsaj3j1j2q845nzja1p-python3.8-requests-2.25.0/lib/python3.8/site-packages/requests/structures.py:54: KeyError

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

fix.md

Option A — Apply the official fix\nFix middleware traceback fetching on Python 3.8+, fix ResourceWarnings in TestClient, and fix CI build.\nWhen NOT to use: Do not apply this fix if using a version of Python older than 3.8.\n\n

Why This Fix Works in Production

Trigger: ============================= test session starts ==============================
Mechanism: Fix middleware traceback fetching on Python 3.8+, fix ResourceWarnings in TestClient, and fix CI build.

Why This Breaks in Prod

Shows up under Python 3.8.7 in real deployments (not just unit tests).
Surfaces as: ============================= test session starts ==============================

Proof / Evidence

GitHub issue: #1131
Fix PR: https://github.com/kludex/starlette/pull/1132
Reproduced locally: No (not executed)
Last verified: 2026-02-11
Confidence: 0.70
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.25

Discussion

High-signal excerpts from the issue thread (symptoms, repros, edge-cases).

Jump to Sources Open on GitHub

“### Checklist  - [x] The bug is reproducible against the latest release and/or master. - [x] There are no similar issues or pull requests to fix it yet. #”

Issue thread · issue description · source

Failure Signature (Search String)

============================= test session starts ==============================

Error Message

Stack trace

error.txt

Error Message
-------------
============================= test session starts ==============================
platform linux -- Python 3.8.7, pytest-6.1.2, py-1.9.0, pluggy-0.13.1
rootdir: /build/source, configfile: setup.cfg
plugins: asyncio-0.14.0, cov-2.10.1
collected 240 items                                                            
[...]
=================================== FAILURES ===================================
_______________________________ test_debug_html ________________________________

    def test_debug_html():
        async def app(scope, receive, send):
            raise RuntimeError("Something went wrong")

        app = ServerErrorMiddleware(app, debug=True)
        client = TestClient(app, raise_server_exceptions=False)
        response = client.get("/", headers={"Accept": "text/html, */*"})
        assert response.status_code == 500
      assert response.headers["content-type"].startswith("text/html")

tests/middleware/test_errors.py:42:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = {}, key = 'content-type'

    def __getitem__(self, key):
      return self._store[key.lower()][1]
E       KeyError: 'content-type'

/nix/store/9bb3iygm8kkdzfsaj3j1j2q845nzja1p-python3.8-requests-2.25.0/lib/python3.8/site-packages/requests/structures.py:54: KeyError

Minimal Reproduction

repro.py

============================= test session starts ==============================
platform linux -- Python 3.8.7, pytest-6.1.2, py-1.9.0, pluggy-0.13.1
rootdir: /build/source, configfile: setup.cfg
plugins: asyncio-0.14.0, cov-2.10.1
collected 240 items                                                            
[...]
=================================== FAILURES ===================================
_______________________________ test_debug_html ________________________________

    def test_debug_html():
        async def app(scope, receive, send):
            raise RuntimeError("Something went wrong")

        app = ServerErrorMiddleware(app, debug=True)
        client = TestClient(app, raise_server_exceptions=False)
        response = client.get("/", headers={"Accept": "text/html, */*"})
        assert response.status_code == 500
      assert response.headers["content-type"].startswith("text/html")

tests/middleware/test_errors.py:42:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = {}, key = 'content-type'

    def __getitem__(self, key):
      return self._store[key.lower()][1]
E       KeyError: 'content-type'

/nix/store/9bb3iygm8kkdzfsaj3j1j2q845nzja1p-python3.8-requests-2.25.0/lib/python3.8/site-packages/requests/structures.py:54: KeyError

Environment

Python: 3.8.7

What Broke

Test failures occurred during package builds on NixOS and Fedora.

Fix Options (Details)

Option A — Apply the official fix

Fix middleware traceback fetching on Python 3.8+, fix ResourceWarnings in TestClient, and fix CI build.

When NOT to use: Do not apply this fix if using a version of Python older than 3.8.

Fix reference: https://github.com/kludex/starlette/pull/1132

Last verified: 2026-02-11. Validate in your environment.

When NOT to Use This Fix

Do not apply this fix if using a version of Python older than 3.8.

Verify Fix

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

Did This Fix Work in Your Case?

Quick signal helps us prioritize which fixes to verify and improve.

Prevention

Add a TLS smoke test that performs a real handshake in CI (include CA bundle validation and hostname checks).
Alert on handshake failures by error string and endpoint to catch cert/CA changes quickly.

Related Issues

No related fixes found.

Cluster: starlette:ssl-handshake All hubs All clusters

Related clusters: Configuration error Data consistency Other

Sources

We don’t republish the full GitHub discussion text. Use the links above for context.