## TL;DR
The warning means a state update happened after the test moved on, usually an async effect resolving after your assertion. Wrap the triggering interaction in `act()`, or better, replace `getBy` queries with `await screen.findByText(...)` so the test waits for the update itself. Once every update settles inside the test body, the warning disappears and CI goes green.

```text
jest "Warning: An update to Component inside a test was not wrapped in act(...)" failing CI with strict mode
```

## Steps
1. Find the warning in the CI log and note which component and which test it names. Run that spec locally with the same strict settings CI uses. Expected: the warning reproduces locally.
2. Look for the state update that escapes the test: a `fireEvent` followed by an immediate assertion, or an effect that fetches data and calls setState after the test finished. Expected: you can point at the interaction whose update lands late.
3. Switch the assertion to an async query that waits for the update: replace `screen.getByText('Saved')` with `await screen.findByText('Saved')`. Expected: the test now waits for the state update instead of racing it.
4. For updates that no query naturally waits on, wrap the trigger: `await act(async function() { fireEvent.click(saveButton) })`. Expected: React flushes the update inside act and the warning is gone.
5. If you use user-event, await every call (`await user.click(button)`), since un-awaited user events are the most common source of escaped updates. Expected: the full spec runs warning-free under strict mode.

## Use this when
- CI fails or warns on "not wrapped in act(...)" while local runs pass
- Tests use React Testing Library with async effects or data fetching
- The warning names your own component's state update

## Not for this skill when
- The warning comes from a third-party library's internals you cannot change (mock the library instead)
- The test failure is a real assertion failure, not the act warning
- You are not testing React components at all

## Variant phrasings
- react testing library act warning failing CI
- update to Component inside a test was not wrapped in act
- jest strict mode act warning how to fix

## Why it happens
React batches state updates, and testing-library's async utilities exist to let those updates settle before assertions run. A synchronous `getBy` assertion (or an un-awaited event) lets the test finish while an effect is still in flight; the late setState then fires outside `act()`, which React flags. Strict mode double-invokes effects, which is why CI (running strict) surfaces what local runs hide.

## Edge cases
- Timers: if the component uses setTimeout, wrap the timer advance in act too, or the update still escapes.
- Multiple sequential updates need each trigger awaited; fixing the first while leaving a second un-awaited just moves the warning.
- Do not silence the warning with a console filter. It is catching a real race between your test and the component.

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_d822vJAeaQneM8tG8X02oA