httpx Fix flaky `test_write_timeout` test in CI (Fix)

The Fix

Upgrade to version 0.13.0 or later.

Based on closed encode/httpx issue #943 · PR/commit linked

Production note: Watch p95/p99 latency and retry volume; timeouts can turn into retry storms and duplicate side-effects.

Open PR/Commit

@@ -4,6 +4,20 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
+## 0.13.0.dev2 (May 12th, 2020)
+
+The 0.13.0.dev2 is a *pre-release* version. To install it, use `pip install httpx --pre`.

fix.md

Option A — Upgrade to fixed release\nUpgrade to version 0.13.0 or later.\nWhen NOT to use: Do not apply this fix if the test failures are due to actual code issues rather than environmental factors.\n\n

Why This Fix Works in Production

Trigger: Fix flaky `test_write_timeout` test in CI
Mechanism: The test_write_timeout test fails intermittently due to environmental issues or dependency changes
Why the fix works: Updates the version to 0.13.0.dev2 and includes various fixes and enhancements. (first fixed release: 0.13.0).

Production impact:

If left unfixed, tail latency can spike under load and surface as timeouts/retries (amplifying incident impact).

Why This Breaks in Prod

The test_write_timeout test fails intermittently due to environmental issues or dependency changes
Production symptom (often without a traceback): Fix flaky `test_write_timeout` test in CI

Proof / Evidence

GitHub issue: #943
Fix PR: https://github.com/encode/httpx/pull/941
First fixed release: 0.13.0
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.71

Discussion

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

Jump to Sources Open on GitHub

“No idea yet, but maybe a change in one of our dependencies...? - pytest-asyncio 0.12, released on May 4th? - Regression in httpcore?”

@florimondmanca · 2020-05-12 · confirmation · source

“#946 might be a bit more reliable here? Really we ought to also look at..”

@lovelydinosaur · 2020-05-12 · source

Failure Signature (Search String)

Fix flaky `test_write_timeout` test in CI
[One of our tests](https://github.com/encode/httpx/blob/master/tests/test_timeouts.py#L15-L22) has decided to start failing across different Python versions:

Copy-friendly signature

signature.txt

Failure Signature
-----------------
Fix flaky `test_write_timeout` test in CI
[One of our tests](https://github.com/encode/httpx/blob/master/tests/test_timeouts.py#L15-L22) has decided to start failing across different Python versions:

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
Fix flaky `test_write_timeout` test in CI
[One of our tests](https://github.com/encode/httpx/blob/master/tests/test_timeouts.py#L15-L22) has decided to start failing across different Python versions:

What Broke

CI tests fail intermittently across different Python versions, causing unreliable test results.

Why It Broke

The test_write_timeout test fails intermittently due to environmental issues or dependency changes

Fix Options (Details)

Option A — Upgrade to fixed release Safe default (recommended)

Upgrade to version 0.13.0 or later.

When NOT to use: Do not apply this fix if the test failures are due to actual code issues rather than environmental factors.

Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.

Fix reference: https://github.com/encode/httpx/pull/941

First fixed release: 0.13.0

Last verified: 2026-02-09. Validate in your environment.

When NOT to Use This Fix

Do not apply this fix if the test failures are due to actual code issues rather than environmental factors.

Did This Fix Work in Your Case?

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

Prevention

Add a CI check that diffs key outputs after upgrades (OpenAPI schema snapshots, JSON payload shapes, CLI output).
Upgrade behind a canary and run integration tests against the canary before 100% rollout.
Make timeouts explicit and test them (unit + integration) to avoid silent behavior changes.
Instrument retries (attempt count + reason) and alert on spikes to catch dependency slowdowns.

Version Compatibility Table

Version	Status
0.13.0	Fixed

Related Issues

No related fixes found.

Cluster: httpx:timeout 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.