React-native-testing-library: Async data load with `useEffect` still triggers `act` warning

[CodingItWrong]

Versions

• React: 16.8.6
• React Native: 0.60.0
• RNTL: 1.10.0
• React-Test-Renderer: 16.8.6

Description

I'm attempting to test asynchronous data loads within useEffect, and I'm getting that old React "An update to [your component] inside a test was not wrapped in act(...)"

I see in #111 that changes were merged related to adding act to various RNTL calls, but that doesn't seem to address this case.

I finally dug through the master React issue on the act warnings, and my main takeaways are:

• For now, use Jest's useFakeTimers and runAllTimers—this is the way Facebook does it and it should work.
• In React 16.9.0 (not released in production yet either for the web or for React Native), act has been updated to support async/await, and so you will be able to do all your stuff in the test inside act, and assert outside of it. Just not released yet.

I tried the "the way Facebook does it" fix and it doesn't seem to work (see reproducible demo below). Do you know of a way to get the test to correctly run this code through act such that I don't get the warning?

Reproducible Demo

https://github.com/CodingItWrong/TestingRNHooks

[thymikee]

Gonna have a look tomorrow, thanks for the report!

[thymikee]

Unfortunately, there's nothing on our side we can do. This is a react-test-renderer issue and needs to be fixed upstream, as said by Sunil: https://github.com/facebook/react/issues/14769#issuecomment-462528230. You can apply various workarounds in your testing environment though:

• mock console.error and filter out those messages for now
• transform async/await to global.Promise and mock it so that it wraps stuff with act, ideally as a helper imported only in React-based tests

However, personally, I try to ignore these warnings 🤷‍♂.

Also, please use await waitForElement(() => getByText('foo')) instead of await flushMicrotasksQueue() – it's easier to read intentions and you don't need to care if async actions take 1 or more microtask ticks.

[neiker]

I added this to my jest setup file, maybe someone find it useful:

const originalConsoleError = console.error;

console.error = (...args) => {
  if (
    !args[0].startsWith(
      'Warning: An update to %s inside a test was not wrapped in act(...).',
    )
  ) {
    originalConsoleError(...args);
  }
};

[thymikee]

Thanks @neiker, appreciated!