# Deflake

Stabilize a flaky test with a minimal, assertion-preserving fix, never by weakening or...

- Repository: https://github.com/QwenLM/qwen-code (28858 stars)
- Category: Testing
- License: Apache-2.0
- Last updated: 2026-11-01
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add QwenLM/qwen-code --skill deflake -g -a claude-code -y`
Codex: `npx skills add QwenLM/qwen-code --skill deflake -g -a codex -y`
Cursor: `npx skills add QwenLM/qwen-code --skill deflake -g -a cursor -y`
Gemini CLI: `npx skills add QwenLM/qwen-code --skill deflake -g -a gemini-cli -y`

## Description

Stabilize a flaky test with a minimal, assertion-preserving fix, never by weakening or deleting the check.

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

# Deflake a flaky test

A `deflake:` issue names ONE test that has been observed failing and then
passing on a rerun of the same commit, the definitive flaky signature. Your
job is to make that test deterministic **without changing what it verifies**.

The issue body carries the test identity (file + name) and the observed failure
signature (e.g. `Test timed out in 5000ms`, `Timed out waiting for …`, an
order-dependent assertion, a wall-clock/random-dependent value). Read the test,
reproduce the mechanism in your head, and apply the SMALLEST fix from the
allowed set below that removes the nondeterminism.

## The only allowed fixes

1. **Raise a timeout / poll budget.** A test that blows vitest's default under
   CI contention (fully-mocked or I/O-bound, not a perf test) gets a generous
   per-test `testTimeout` (3rd arg to `it`), or its internal poll loop is given
   a real wall-clock budget instead of a fixed iteration count (a fixed count of
   `setImmediate` turns elapses in milliseconds and races real I/O).
2. **Stabilize timing / waiting.** Replace a bare `setTimeout`/fixed `sleep`
   with an explicit `await` of the real condition (`vi.waitFor`, a resolved
   promise, an event). Pre-warm a lazy load (e.g. a WASM runtime) in
   `beforeAll` so per-test time doesn't include first-load cost.
3. **Make randomness / time deterministic.** Seed the RNG, `vi.useFakeTimers()`
   / mock `Date.now`, or pin the input so a value that depends on the real clock
   or `Math.random` can't drift.
4. **Isolate / serialize interference.** Give tests that collide on a shared
   resource (a same-named tempdir, a fixed port, a global singleton) unique
   per-test resources, or serialize them.

## Hard rules

The rest: https://github.com/QwenLM/qwen-code/blob/HEAD/.qwen/skills/deflake/SKILL.md