Custom Jest matcher for AsyncIterable contents equality

jest-async-iterator.ts

declare global {
  namespace jest {
    interface Matchers<R> {
      toEqualAsyncIterator<T, TReturn>(expected: AsyncIterator<T, TReturn>): R;
    }
  }
}

expect.extend({
  async toEqualAsyncIterator<T, TReturn>(
    got: AsyncIterator<T, TReturn>,
    expected: AsyncIterator<T, TReturn>
  ) {
    const [expectedValues, actualValues] = await Promise.all(
      [got, expected].map(async function collect(iter) {
        const { value, done } = await iter.next();
        return [value].concat(done ? [] : await collect(iter));
      })
    );

    expect(expectedValues).toEqual(actualValues);

    return {
      pass: true,
      message: () => `Expected ${got} to equal ${expected}`,
    };
  },
});