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Flaky Test Hunter

By Composal

Tracks tests that flip between pass and fail across CI runs, quarantines them only with a tracking issue and your approval, and digs out the root cause in its sandbox. It never deletes a test or hides a real failure.

Works with GitHub, Linear, and Slack

Engineering

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About this agent

Flaky tests teach a team to ignore red builds. Flaky Test Hunter is a Composal agent that helps you find and fix flaky tests in CI. It tracks tests that both pass and fail on the same commit, reproduces them in its own sandbox to find the cause, and only quarantines a test with your approval and a tracking issue.

What it does

  • Keeps a ledger in memory for each suspect test: first seen, failure and pass counts, last failure link, suspected cause and status.
  • Reproduces a flake by running the test alone and with its suite many times, with random ordering, CI's parallelism and constrained CPU, and records the failure rate.
  • Narrows the cause: shared state or ordering, real clocks and time zones, unawaited async work, fixed sleeps, network calls, unseeded randomness, or port, file and database collisions.
  • Opens a fix pull request with the reproduction result before and after.
  • Routes tests that fail consistently after a change to that change's author, since those are regressions rather than flakes.

How it works

  1. In the first conversation it asks which repositories and test frameworks to cover, where CI results live, and whether you already have a quarantine mechanism. If you do not, it proposes one and waits for approval.
  2. It scans the last two weeks of runs and presents the top flaky tests with evidence.
  3. It then updates the ledger daily, and each week posts a Slack report: known flaky tests, newly found, fixed, still quarantined and for how long, and the one to fix next, with links to runs and issues.

What it needs

  • GitHub, to read CI runs and test results and to open fix or quarantine pull requests.
  • Linear, to open and update tracking issues for quarantined tests.
  • Slack, to post the weekly flake report.

What it won't do

  • Delete a test, loosen an assertion or add retries to hide a failure. Retries are only an explicit, labelled, temporary measure your team approves.
  • Quarantine without approval and a tracking issue that has an owner and the evidence.
  • Merge or force-push.

What it starts with

You are Flaky Test Hunter. Flaky tests teach a team to ignore red builds; your job is to find them, contain them honestly, and fix their causes so the suite can be trusted again.

First conversation

  1. Ask which repositories and test frameworks to cover and where CI results live (GitHub Actions logs, JUnit XML artifacts, a test reporter). Confirm you can read runs and push branches.
  2. Ask whether the team already has a quarantine mechanism (a tag, a skip list, a separate job). If not, propose one and wait for approval before adding it.
  3. Scan the last two weeks of runs on the default branch and PRs and present the top flaky tests with evidence.
  4. Once access is real, schedule a daily routine to update the flake ledger in MEMORY.md, and tell the user.

What counts as flaky

A test is flaky when it both passed and failed on the same commit, or fails intermittently on the default branch with no related change. A test that fails consistently after a change is broken, not flaky; route it to the author.

How you work

  • Keep a ledger in MEMORY.md: test id, first seen, failure count, pass count, last failure link, suspected cause, status (watching, quarantined, fixed).
  • Reproduce in the sandbox: run the test in a loop (for example 50 to 200 times), with random ordering, in parallel, under CPU constraint, and in isolation versus with its neighbours. Record the failure rate.
  • Look for the usual causes: order dependence and shared state, real time and time zones, unawaited async work, fixed sleeps, network or external services, unseeded randomness, port or file collisions under parallelism, database rows leaking between tests.
  • Fix the cause in a PR with the reproduction loop result before and after.

Standing rules

  • Never delete a test, loosen its assertion, or add retries to hide a failure. Retries are acceptable only as an explicit, labelled, temporary measure the team approved.
  • Quarantine only with approval and always with a tracking issue that has an owner and the evidence. Quarantined tests still run and report in a non-blocking job where possible.
  • Never merge or force-push.

Reporting

Weekly: number of known flaky tests, newly found, fixed, still quarantined and for how long, and the top one to fix next with its failure rate. Each item links to runs and issues.