--- title: "Wait for the state transition before asserting" description: "Synchronize with the event that makes the assertion true, so the test stops needing reruns." url: https://starsling.dev/ci-playbooks/techniques/synchronize-assertions canonicalUrl: https://starsling.dev/ci-playbooks/techniques/synchronize-assertions --- # Wait for the state transition before asserting Synchronize with the event that makes the assertion true, so the test stops needing reruns. ## How to choose an approach This technique currently has one documented company example. Validate its prerequisites, tradeoffs and original CI environment against your repository before adapting it. - **[Uber](https://starsling.dev/ci-playbooks/uber#synchronize-assertions)**: Use it when A test observes asynchronous state before the operation that updates it completes. Check before adopting: Wait for the specific event under test with a bounded timeout, keep the assertions, and confirm the signal comes from the operation being tested. ## Apply this technique ````text Evaluate and apply this CI technique to my repository: Wait for the state transition before asserting. Synchronize with the event that makes the assertion true, so the test stops needing reruns. Read the technique and its source-backed company examples: https://starsling.dev/ci-playbooks/techniques/synchronize-assertions.md Inspect this repository’s CI workflows, build and test commands, dependencies, and recent run timings. Identify where this technique applies and explain the expected benefit using this repository’s evidence. Measure a baseline from recent comparable runs: elapsed time, queue time, runner minutes and failures where available. If data is unavailable, say what cannot be measured. Compare relevant company approaches, checking prerequisites, platform differences and tradeoffs. Rank applicable options by evidence, fit and measurable opportunity; do not present company results as predictions for this repo. Recommend the smallest safe change, show what checks and fallback paths remain, and ASK ME WHICH CHANGE TO APPROVE BEFORE EDITING ANY FILES. Only after approval, work on a new feature branch, make one reversible change, and open a reviewable pull request. Never merge or push to a default or protected branch. Keep required checks, test coverage, deployment and release behavior intact. Validate the change and compare equivalent runs where possible; report limitations and what should be monitored after merge. ```` ## How Uber used this technique Read what Uber changed and follow the original sources. ### Uber: Wait for the state transition before asserting A SubmitQueue integration test checked consumer lag right after acknowledging a delivery, while the queue updated its watermark on the next poll tick. The fix waits for a delivery-check signal before reading lag. OPT48 is adapted to one flaky test. Evidence: Source PR/commit evidence The author ran the test 50 times locally, all passing. ([Source](https://github.com/uber/submitqueue/pull/274)) Use it when: A test observes asynchronous state before the operation that updates it completes. Before applying it: Wait for the specific event under test with a bounded timeout, keep the assertions, and confirm the signal comes from the operation being tested. [Read more in the Uber playbook](https://starsling.dev/ci-playbooks/uber#synchronize-assertions) [Primary source](https://github.com/uber/submitqueue/pull/274) ## CI optimization is continuous work. Apply this technique yourself, or use StarSling Runners for faster GitHub Actions and optional agent-driven optimization PRs, which teams on eligible paid plans can turn on. [Get self-improving CI](https://starsling.dev/products/runners) ## Related techniques ### [Check for leaks after this test cleans up](https://starsling.dev/ci-playbooks/techniques/check-cleanup-at-test-end) Run the leak check at the end of the test, where it inspects this test's own resources. 1 implementation · 1 company (Uber) ### [Make unordered results deterministic before comparing](https://starsling.dev/ci-playbooks/techniques/normalize-unordered-results) Sort values whose order was never guaranteed, so an equivalent result passes on the first run. 1 implementation · 1 company (Uber) ### [Prove a new test is stable before it joins the blocking suite](https://starsling.dev/ci-playbooks/techniques/flakiness-gate-before-blocking) Run each new end-to-end test many times in a dedicated pipeline, and admit it to the blocking checks only if it stays under a failure threshold. 1 implementation · 1 company (Shopify) ## Company Playbooks ### [Anthropic](https://starsling.dev/ci-playbooks/anthropic) Run only affected tests ### [DoorDash](https://starsling.dev/ci-playbooks/doordash) Run build and test in parallel, sharded across CI agents ### [Linear](https://starsling.dev/ci-playbooks/linear) Benchmark the same job on faster hardware ### [Mastra](https://starsling.dev/ci-playbooks/mastra) StarSling runners for the slowest test workflow ### [OpenAI](https://starsling.dev/ci-playbooks/openai) Rank CI fixes by the minutes they save ### [Ramp](https://starsling.dev/ci-playbooks/ramp) Move a CPU-bound test suite to a faster CPU ### [Shopify](https://starsling.dev/ci-playbooks/shopify) Let an agent iterate against one CI metric ### [Spotify](https://starsling.dev/ci-playbooks/spotify) Build arm64 on native arm64 runners ### [Stripe](https://starsling.dev/ci-playbooks/stripe) Run only the tests a change can reach ### [Uber](https://starsling.dev/ci-playbooks/uber) Build the merge-queue speculations most likely to be needed ## Related guides Implementation guides for this technique. ### [Replace fixed CI sleeps with bounded readiness polling](https://starsling.dev/best-practices/github-actions/replace-fixed-sleeps-with-polling) Replace fixed sleeps in CI tests with bounded readiness polling that exits as soon as the exact condition is ready and fails with useful diagnostics.