Tests failures in React 19's concurrent mode

[roni-castro-shipt]

We’re working on a project where approximately 600 tests are failing when React 19's Concurrent Mode (concurrentRoot: true) is enabled by default without breaking any user feature.
In our previous setup (React 18 / V13 / concurrentRoot: false), all tests like the ones shared below were passing, but they are now consistently failing.

I understand how to fix them — using fireEvent, userEvent, or wrapping with act — but I'm wondering:
Is there an alternative way to make these tests compatible with React 19 without having to manually update all 600 tests at once — allowing us to gradually migrate over time — and without needing to add act around every function that triggers a state update?

Example 1 (missing async act)

    await store.setPayPeriodDetails({ startDate: 'startDate', endDate: 'endDate', currentPage: 1 });

    expect(store.state.transactionsData).toMatchSnapshot('transactionsData');
    expect(OrderHistoryService.fetchPayPeriodDetails).toHaveBeenCalledTimes(1);

would need to be updated to

     await act(async () => {
      await store.setPayPeriodDetails({ startDate: 'startDate', endDate: 'endDate', currentPage: 1 });
    });

    expect(store.state.transactionsData).toMatchSnapshot('transactionsData');
    expect(OrderHistoryService.fetchPayPeriodDetails).toHaveBeenCalledTimes(1);

Example 2 (missing act)

     wrapper.getByTestId(CHAT_MESSAGE.VIDEO).props.onError();

    expect(wrapper.getByTestId(CHAT_MESSAGE.UNSUPPORTED_FILE_ERROR).props).toMatchSnapshot();

would need to be updated to

    act(() => {
      wrapper.getByTestId(CHAT_MESSAGE.VIDEO).props.onError();
    });

    expect(wrapper.getByTestId(CHAT_MESSAGE.UNSUPPORTED_FILE_ERROR).props).toMatchSnapshot();

Example 3 (missing fireEvent/userEvent)

    wrapper.getByTestId(CHAT_MODAL.TEXT_INPUT).props.onChangeText('text or something else');
    await fireEvent.press(wrapper.getByTestId(CHAT_MODAL.SCAN_ICON));

    expect(wrapper.getByTestId(CHAT_MODAL.TEXT_INPUT).props.value).toEqual('text or something else');

would need to be updated to

    await user.type(wrapper.getByTestId(CHAT_MODAL.TEXT_INPUT), 'text or something else'); // usage of user.type or fireEvent.changeText
    fireEvent.press(wrapper.getByTestId(CHAT_MODAL.SCAN_ICON));

    expect(wrapper.getByTestId(CHAT_MODAL.TEXT_INPUT)).toHaveDisplayValue('text or something else');

Example 4 (missing fireEvent/userEvent)

    input.props.onChangeText('5');
    input.props.onEndEditing();

    expect(input.props.value).toEqual('5.0');

would need to be updated to:

    await user.paste(input, '5'); // usage of user.paste or fireEvent

    expect(input).toHaveDisplayValue('5.0');

[mdjastrzebski]

I am working on better concurrent mode support in #1788 but that concerns mainly tests with Suspense element.

Regarding your tests, even in React 18, you should wrap your code that triggers re-renders in act, as it allows React to run sync effects. With React 19 that changes to await act(async () => { ... }) due to concurrent mode.

When you use relevant User Event interactions, as that gives you much more realistic testing, as User Event emits sequence of multiple event for each interaction, e.g. onPressIn, onPress, onPressOut for press and for type it simulates user typing letter by letter with numerous events triggered for each letter.

[williamgurzoni]

I'm having the same problems with act. Previously, my tests were running smoothly with no act needed. My understanding was that the testing library was already wrapping it for me as stated here:

React Act

Does it change completely on React 19?

[roni-castro-shipt]

@mdjastrzebski Why does RNTL use sync act in render, fireEvent... and not async act, given React does not recommend using the sync version?

[mdjastrzebski]

Working on it in #1788, this seems to be quite recent addition to RN, connected with React 19 switch.