Having to use an empty `act` immediately after render to avoid warning

[leepowellnbs]

I have a component, which does some async loading of data from various sources - some coming from within the component itself, and some coming from a wrapped context - all take place in useEffect hooks. I'm finding I'm having to use empty act calls to avoid the act warning - contrived example:

const screen = render(<MyComponent />, { wrapper: <MyContextProviders />});

expect(await screen.findByText('Hello')).toBeTruthy();

In this example I get the "not wrapped in an act" warning from where one of the context providers is fetching data on mount. The odd thing, is the component doesn't render Hello until this data fetching is finished and the fetched data is available.

To suppress the error I am having to add an empty act:

const screen = render(<MyComponent />, { wrapper: <MyContextProviders />});

await act(async () => {});

expect(await screen.findByText('Hello')).toBeTruthy();

I have no idea why but this seems to work. Could anyone help me understand why this works, or if there is a better way of doing this - as it feels a bit hacky. Thanks.

EDIT: Just remembered, the data loading function called by the provider is async - and once the data resolves it sets state, which is what is seemingly triggering the act warning.

[mdjastrzebski]

@leepowellnbs can you post a minimal repro repository that showcases the issue & fix?

[leepowellnbs]

@mdjastrzebski sure I'll try to pull one together - I was trying to do so yesterday when I came across this strange behaviour https://github.com/callstack/react-native-testing-library/issues/1067

[mdjastrzebski]

@leepowelldev could you check if this issue still occurs with RNTL v11.2.0?

[jake-carpenter]

I'm also seeing this issue in RNTL v9.1.0 with Jest 26.6.3 after upgrading to RN 0.69 (using Expo SDK 46). I don't mean to hijack this discussion - let me know if this warrants discussion and another ticket.

We've previously moved away from queries like await waitForElementToBeRemoved(() => view.getByLabelText('Loading')) in favor of await view.findByLabelText('Foo') which would wait for loading state go go away. Now a huge chunk of tests that do this are actually failing, not just throwing the warning about using act(). This hack solves the problem, but clearly it's not ideal.

Is there a workaround for older versions of RNTL? I'm unable to upgrade at the moment thanks to a package using RN Reanimated.

[AugustinLF]

Is there a workaround for older versions of RNTL

That's going to be complicated, because RN 0.69 comes with react 18 which uses a different model for act, and we had to change quite a bit of things for it. You could try using a patch package and reimplement the changes, but that sounds like quite a hassle.

Regarding you RN reanimated issue, could a global mock work?

[jake-carpenter]

That's going to be complicated, because RN 0.69 comes with react 18 which uses a different model for act, and we had to change quite a bit of things for it. You could try using a patch package and reimplement the changes, but that sounds like quite a hassle.

Regarding you RN reanimated issue, could a global mock work?

That's what I was afraid of. I'll move forward with using this act() hack to hide my problem for now, but probably get started on removing my dependency on react-native-reanimated, unless their fix gets merged soon.

[mdjastrzebski]

Closing as original issue hasn't seen any action since August.

@leepowellnbs if the issue still occurs to you pls create a new issue with minimal repro repo based on our examples/basic.

@jake-carpenter Pls create a separate issue with minimal repro repo if needed.