feat: add auto-mock support for async generators

[shooit]

Summary

Adds async generators to the types of functions that will be auto-mocked

Test plan

yarn jest "generator" passes

[SimenB]

Cool! If that is invoked, is it a generator? I believe we have some inference for that

[shooit]

I'm not sure I understand the question fully but here's an example of the behavior I would expect with comments about the current behavior.

I would be more than happy to add these tests to the suite as well but wasn't sure where the appropriate place was so I just tried to match what was already included in #5983

index.ts

export function* generator(): IterableIterator<number> {
  yield 1;
  yield 2;
  yield 3;
}

export async function* asyncGenerator(): AsyncIterableIterator<number> {
  yield 1;
  yield 2;
  yield 3;
}

index.test.ts

import { mocked } from "ts-jest/utils";
import * as sut from "../index";

function* arrayToIterableIterator<T>(arr: T[]): IterableIterator<T> {
  for (const item of arr) {
    yield item;
  }
}

async function* arrayToAsyncIterableIterator<T>(arr: T[]): AsyncIterableIterator<T> {
  for (const item of arr) {
    yield item;
  }
}

const mockedValue = [4, 5, 6];

test("generator mocks correctly", () => {
  mocked(sut.generator).mockReturnValue(arrayToIterableIterator(mockedValue));
  const arr = Array.from(sut.generator());
  expect(arr).toEqual(mockedValue); // this passes 👍 
});

test("async generator mocks correctly", async () => {
  // this currently throws: TypeError: Cannot read property 'mockReturnValue' of undefined
  mocked(sut.asyncGenerator).mockReturnValue(arrayToAsyncIterableIterator(mockedValue));
  const arr: number[] = [];
  // Array.from does not work for async generators so we iterate and push the values instead
  for await (const value of sut.asyncGenerator()) {
    arr.push(value);
  }
  expect(arr).toEqual(mockedValue);
});

[SimenB]

thanks!

[SimenB]

https://github.com/facebook/jest/releases/tag/v28.0.0-alpha.5

[github-actions]

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