prefer-expect-resolves.md

Prefer await expect(...).resolves over expect(await ...) syntax (prefer-expect-resolves)

When working with promises, there are two primary ways you can test the resolved value:

1. use the resolve modifier on expect (await expect(...).resolves.<matcher> style)
2. await the promise and assert against its result (expect(await ...).<matcher> style)

While the second style is arguably less dependent on jest, if the promise rejects it will be treated as a general error, resulting in less predictable behaviour and output from jest.

Additionally, favoring the first style ensures consistency with its rejects counterpart, as there is no way of "awaiting" a rejection.

Rule details

This rule triggers a warning if an await is done within an expect, and recommends using resolves instead.

Examples of incorrect code for this rule

it('passes', async () => {
  expect(await someValue()).toBe(true);
});

it('is true', async () => {
  const myPromise = Promise.resolve(true);

  expect(await myPromise).toBe(true);
});

Examples of correct code for this rule

it('passes', async () => {
  await expect(someValue()).resolves.toBe(true);
});

it('is true', async () => {
  const myPromise = Promise.resolve(true);

  await expect(myPromise).resolves.toBe(true);
});

it('errors', async () => {
  await expect(Promise.rejects('oh noes!')).rejects.toThrow('oh noes!');
});