jest/prefer-expect-resolves Style

🛠️ An auto-fix is available for this rule.

What it does

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.

Example

// valid
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.reject(new Error("oh noes!"))).rejects.toThrowError("oh noes!");
});

// invalid
it("passes", async () => {
  expect(await someValue()).toBe(true);
});
it("is true", async () => {
  const myPromise = Promise.resolve(true);
  expect(await myPromise).toBe(true);
});

References

• Rule Source