manually flush microtasks in afterEach

[LaurensBosscher]

This is the rebase of #440. I've squashed both commits into the original commit.

Original description:

This PR replaces calling async act() in afterEach, with a version that still flushes microtasks, but doesn't wrap with act().

Explanation: If there are any hanging microtasks, that means a test ran without asserting on a valid state. Any async portion that causes updates should be asserted on, or atleast resolved within the scope of a test. This PR should still fire missing act warnings for a test, but won't let it leak to the next one.

[kentcdodds]

I'd like a review from one other maintainer, but I think this is acceptable.

[kentcdodds]

@all-contributors please add @LaurensBosscher code

[allcontributors]

@kentcdodds

I've put up a pull request to add @LaurensBosscher! 🎉

[kentcdodds]

🎉 This PR is included in version 9.3.1 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀

[evoyy]

I just upgraded to 9.3.1 and this is causing my test suite to log the following error:

ERROR: true, 'This browser does not have a MessageChannel implementation, so enqueuing tasks via await act(async () => ...) will fail. Please file an issue at https://github.com/facebook/react/issues if you encounter this warning.'

Is this something I need to worry about? I'm running my tests in Chrome using Karma.

[kentcdodds]

cc @threepointone

[donaldpipowitch]

This was the only change from v9.3.0 to v9.3.1, right? When I switch between those versions I get An update to Formik inside a test was not wrapped in act(...). in every case where a fireEvent.change is not followed by an await. fireEvent.click seems to be fine. Is this intended behavior?

[eps1lon]

@donaldpipowitch Please open a new issue with a reproducible example. Without code it's hard to tell whether this is intended or not.

[donaldpipowitch]

@eps1lon I created the bug report: #535