#Async utilities

#findBy* queries

The findBy* queries are used to find elements that are not instantly available but will be added as a result of some asynchronous action. Learn more details here.

#waitFor

function waitFor<T>(
  expectation: () => T,
  options?: {
    timeout?: number;
    interval?: number;
    onTimeout?: (error: Error) => Error;
  }
): Promise<T>;

Waits for the expectation callback to pass. waitFor runs the callback multiple times until timeout is reached, as specified by the timeout and interval options. The callback must throw an error when the expectation is not met. Returning any value, including a falsy one, is treated as meeting the expectation, and the callback result is returned to the caller.

await waitFor(() => expect(mockFunction).toHaveBeenCalledWith());

waitFor executes the expectation callback every interval (default: 50 ms) until timeout (default: 1000 ms) is reached. Execution stops as soon as the callback doesn't throw an error, and the callback's return value is returned to the caller. If timeout is reached, waitFor re-throws the final error thrown by expectation.

// ❌ `waitFor` will return immediately because callback does not throw
await waitFor(() => false);

waitFor is an async function so you need to await the result to pause test execution.

// ❌ missing `await`: `waitFor` will just return Promise that will be rejected when the timeout is reached
waitFor(() => expect(1).toBe(2));

Since waitFor runs the expectation callback multiple times, avoid performing side effects in waitFor.

await waitFor(async () => {
  // ❌ button will be pressed on each waitFor iteration
  await fireEvent.press(screen.getByText('press me'));
  expect(mockOnPress).toHaveBeenCalled();
});

Use a single assertion per waitFor for consistency and faster failing tests. For multiple assertions, use separate waitFor calls. Often you won't need to wrap the second assertion in waitFor since the first one waits for the asynchronous change.

waitFor checks whether Jest fake timers are enabled and adapts its behavior in such case. The following snippet is a simplified version of how it behaves when fake timers are enabled:

let fakeTimeRemaining = timeout;
let lastError;

while (fakeTimeRemaining > 0) {
  fakeTimeRemaining = fakeTimeRemaining - interval;
  jest.advanceTimersByTime(interval);
  try {
    // resolve
    return expectation();
  } catch (error) {
    lastError = error;
  }
}

// reject
throw lastError;

In the following example we test that a function is called after 10 seconds using fake timers. With fake timers, the test doesn't depend on real time passing, making it faster and more reliable. We don't need to advance fake timers through Jest's API because waitFor handles this.

// in component
setTimeout(() => {
  someFunction();
}, 10000);

// in test
jest.useFakeTimers();

await waitFor(
  () => {
    expect(someFunction).toHaveBeenCalledWith();
  },
  { timeout: 10000 }
);

#Options

• timeout: How long to wait for, in ms. Defaults to 1000 ms (configured by asyncUtilTimeout option).
• interval: How often to check, in ms. Defaults to 50 ms.
• onTimeout: Callback to transform the error before it's thrown. Useful for debugging, e.g., onTimeout: () => { screen.debug(); }.

#waitForElementToBeRemoved

function waitForElementToBeRemoved<T>(
  expectation: () => T,
  options?: {
    timeout?: number;
    interval?: number;
    onTimeout?: (error: Error) => Error;
  }
): Promise<T>;

Waits for non-deterministic periods of time until queried element is removed or times out. waitForElementToBeRemoved periodically calls expectation every interval milliseconds to determine whether the element has been removed or not.

import { render, screen, waitForElementToBeRemoved } from '@testing-library/react-native';

test('waiting for an Banana to be removed', async () => {
  await render(<Banana />);

  await waitForElementToBeRemoved(() => screen.getByText('Banana ready'));
});

This method expects that the element is initially present in the render tree and then is removed from it. If the element is not present when you call this method it throws an error.

You can use any of getBy, getAllBy, queryBy and queryAllBy queries for expectation parameter.