# Flaky Test Detection

> Detect, prevent, and fix flaky Jest unit tests in MetaMask Mobile before they reach CI. Use this skill when: reviewing a PR diff or changed test files for flakiness risk, fixing an intermittently failing Jest test, reproducing a flaky test locally, or auditing GitHub Actions history to rank historically flaky unit tests by failure rate.

- Skill: `metamask/flaky-test-detection` (Agent Skill, multi-file: 4 files)
- Install (CLI): `npx skillmds@latest add metamask/flaky-test-detection`
- Raw SKILL.md: https://api.skillmd.com/api/skills/metamask/flaky-test-detection/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: metamask (https://skillmd.com/u/metamask)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/metamask/flaky-test-detection

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# Flaky Test Detection

```
Task → Which mode?
├─ Reviewing changed test files / PR diff for risk patterns  → Review mode
├─ Fixing a known flaky Jest unit test                       → Review mode + local reproduce loop
└─ Auditing CI history to rank flaky tests by failure rate   → open references/gh-analysis.md
```

## Constraints

All proposed fixes must comply with `mms-mobile-testing` (unit path) and `mms-coding-guidelines`. Key rules:
- Use `jest.mocked(fn)` — never `fn as jest.Mock`
- Use `toBeOnTheScreen()` — never `toBeTruthy()` / `toBeDefined()` for element presence
- Use `yarn` commands — never npm or npx
- No `toMatchSnapshot()` — use explicit assertions or `toMatchInlineSnapshot()`

## Review mode

1. Scan changed `.test.ts(x)` files against the pattern table (J1–J10).
2. Classify each hit (async / timing / isolation / mock / state).
3. Propose the fix for each hit using the ✅ pattern from the matching section — apply only on explicit confirmation.
4. Run the local reproduction loop to confirm the fix holds.

## Audit mode

Query GitHub Actions run history to produce a ranked list of historically flaky unit test files with failure rates and suggested fix categories.

Open [references/gh-analysis.md](references/gh-analysis.md) for the full procedure.