Imported from maddhruv/absolute (
skills/absolute-deflake/SKILL.md). Install upstream withnpx skills add maddhruv/absolute --skill absolute-deflake. Copyright stays with the author (MIT).
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Absolute Deflake
Find tests that pass and fail nondeterministically, diagnose the root cause of each, and fix it — not by retrying or skipping, but by removing the source of nondeterminism. Output is evidence (failure rate per test) → cause → fix, verified by repeated runs.
Runs the shared engine in references/health-engine.md — read it for the
DETECT → SCAN → TRIAGE → FIX → VERIFY → REPORT loop and the safety contract. This file
covers only what's specific to flaky tests.
When to use
- "Our CI is flaky", "this test fails randomly", "fix the intermittent failures".
- A test passes locally but fails in CI (or vice versa), or fails ~1 in N runs.
- Burning down a backlog of
retry/skip-marked tests that mask real flakiness.
Not for tests that fail deterministically — that's a real bug or a real regression
(/absolute work for a fix, or just fix it). deflake targets nondeterministic failures.
What it scans
Establish flakiness empirically — a test isn't flaky because someone said so. Use
preferences.health.deflakeRuns from config as the default N for repeat-runs (else 20):
| Ecosystem | Repeat-run / detect |
|---|---|
| Jest/Vitest | run suite N× (--run loop), randomize order (--shuffle / testSequencer) |
| pytest | pytest-randomly + pytest --count=N (pytest-repeat); -p no:randomly to A/B |
| Go | go test -count=N -shuffle=on ./..., -race |
Also mine signals: existing retry/flaky/skip annotations, CI history if reachable, and
run the suite both in isolation and in full/parallel — order- and concurrency-
dependent failures only show one way. Record a failure rate per suspect test.
Common root causes (diagnose, don't guess)
| Cause | Tell | Fix |
|---|---|---|
| Test-order / shared state | passes alone, fails in suite (or vice versa) | isolate state; reset/teardown between tests |
| Time / clock | fails near midnight, DST, or under load | fake timers / inject clock; no real sleep |
| Async race / missing await | fails under parallelism or slow CI | await the actual condition; no fixed timeouts |
| Randomness | fails ~X% with no pattern | seed the RNG; fix the seed in tests |
| Network / external I/O | fails offline or on slow links | mock/stub the boundary |
| Unordered collections | fails on map/set iteration order | sort before asserting |
| Resource leak / port reuse | fails on repeat or parallel runs | unique resources; clean up |
Risk ranking (TRIAGE)
| Wave | Class | Default |
|---|---|---|
| 1 | clear, isolated cause (seed, await, fake clock, sort) | fix now |
| 2 | shared-state / ordering — needs fixture refactor | fix this pass, per test |
| 3 | flakiness pointing at a real product race, not just the test | gated — surface; may be a genuine bug to fix in code |
A flaky test sometimes means the code has a race, not the test. Don't "stabilize" the test into hiding a real concurrency bug — flag wave-3 cases for a real fix.
Fix & verify
- Fix the cause. Then prove it: re-run the test many times (and shuffled / parallel /
with
-race) — green once is not deflaked; green across N randomized runs is. - Remove the
retry/skip/flakyannotation that was masking it once the cause is fixed. - Never "fix" by adding retries, raising timeouts blindly,
sleep, or skipping the test — that hides flakiness, doesn't remove it. - Re-run the full suite to confirm the fix didn't destabilize neighbors.
Gotchas
- Retry/skip as a fix. Masks the flake, ships the nondeterminism. Forbidden here.
sleepto dodge a race. Slows the suite and still flakes under load. Await the condition.- One green run = done. Flakes are probabilistic — verify with many randomized runs.
- Stabilizing a real product race. If the code races, fix the code, not just the assertion.
- Ignoring order/parallel dimension. Run isolated and in-suite; the bug hides in whichever you skip.
Companion commands
/absolute upgrade— a flaky suite makes upgrade verification unreliable; deflake first./absolute debt— flaky-test annotations are test debt; this clears them at the root./absolute work— when the flake is a genuine product-code race needing real design.