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API

Several utilities are provided for dealing with asynchronous code. These can be useful to wait for an element to appear or disappear in response to an event, user action, timeout, or Promise. (See the guide to testing disappearance.)

The async methods return Promises, so be sure to use await or .then when calling them.

waitFor

function waitFor<T>(
  callback: () => T | Promise<T>,
  options?: {
    interval?: number
    onTimeout?: (error: Error) => Error
    showOriginalStackTrace?: boolean
    signal?: AbortSignal
    timeout?: number
  },
): Promise<T>

When in need to wait for any period of time you can use waitFor, to wait for your expectations to pass. Here's a simple example:

// ...
// Wait until the callback does not throw an error. In this case, that means
// it'll wait until the mock function has been called once.
await waitFor(() => expect(mockAPI).toHaveBeenCalledTimes(1))
// ...

waitFor may run the callback a number of times until the timeout is reached. Note that the number of calls is constrained by the timeout and interval options.

This can be useful if you have a unit test that mocks API calls and you need to wait for your mock promises to all resolve.

If you return a promise in the waitFor callback (either explicitly or implicitly with the async syntax), then the waitFor utility does not call your callback again until that promise rejects. This allows you to waitFor things that must be checked asynchronously.

The default interval is 50ms. However, it runs your callback immediately before starting the intervals.

The onTimeout callback receives the error with which waitFor should reject. You can return a more detailed error with which waitFor should reject. For example, in a DOM you can return a snapshot of the DOM at the time waitFor timed out.

You can pass an AbortSignal if you want waitFor to stop checking the callback (e.g. if you want it to race against other observers like MutationObserver). waitFor will then reject with the reason of the given AbortSignal.

By default, waitFor will reject with the stack trace of the waitFor call. This is usually the more relevant stack trace for developers. However, you might want to trace the last call to the given callback that caused waitFor to reject. Then you can pass showOriginalStackTrace: true. We don't recommend using it unless you know what you're doing.

The default timeout is 1000ms.