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Andrew ClarkandRick Hanlon
214b06140b
`use` can avoid suspending on already resolved data by yielding to microtasks. In a real, browser environment, we do this by scheduling a platform task (i.e. postTask). In a test environment, tasks are scheduled on a special internal queue so that they can be flushed by the `act` testing API. So we need to add support for this in `act`. This behavior only works if you `await` the thenable returned by the `act` call. We currently do not require that users do this. So I added a warning, but it only fires if `use` was called. The old Suspense pattern will not trigger a warning. This is to avoid breaking existing tests that use Suspense. The implementation of `act` has gotten extremely complicated because of the subtle changes in behavior over the years, and our commitment to maintaining backwards compatibility. We really should consider being more restrictive in a future major release. The changes are a bit confusing so I did my best to add inline comments explaining how it works. ## Test plan I ran this against Facebook's internal Jest test suite to confirm nothing broke