`@testduet/wait-for`

Adopted from @testing-library/dom and work without DOM implementation.

Loop a function and spin-wait until it return or resolve.

Background

@testing-library/dom has an excellent waitFor() function. It helps simplifying tests. However, the function requires DOM implementation.

This package adopted the waitFor() function with some modificiations:

Ported to TypeScript
Removed DOM-related code
Added support of Sinon.JS fake timers, in additional to Jest fake timers

How to use

The following code resolve and reject based on probability. If the promise is being rejected, waitFor() will rerun it until timeout. The default timeout is 1 second and rerun interval is 50 milliseconds.

import { waitFor } from '@testduet/waitfor`;

it('should work', async () => {
  await waitFor(
    () =>
      /** @type {Promise<void>} */
      new Promise((resolve, reject) => setTimeout(() => (Math.random() > 0.5 ? resolve() : reject()), 100))
  );
});

If the function does not resolve before timeout, the last error will be thrown.

waitFor() works with Jest fake timers. Supports of Sinon.JS fake timers is added to this package. The spin-wait will automatically advance fake timers.

Behaviors

What are the differences between `@testing-library/dom` and this package?

This package adopted the code from @testing-library/dom@10.4.0
This package works without DOM implementation
- @testing-library/dom version is recommended when working with DOM
  - Better diagnostic information related to DOM
  - MutationObserver on the whole document to speed up spin-wait
This package added support of Sinon.JS fake timers

Why are my tests generating many test snapshots?

Consider using expect().toMatchInlineSnapshot() instead of expect().toMatchSnapshot().

waitFor() expects the callback function to be idempotent. The callback function will be called multiple times until it succeed.

If expect().toMatchSnapshot() is placed inside the callback function, it will be called multiple times until the snapshot passed. This could generates many test snapshots.

Contributions

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Package detail