Fix crash when Promise rejects with null

[Pajn]

Fixes #6896
Jest crashed / Shows test failure from exception inside Kest

it('should just fail the test', () => {
  return Promise.reject(null)
})

Test story:

Help wanted!
How do I test this? Adding a simple unittest to is_error does not really show how it fixes the actual problem.

[codecov-io]

Codecov Report

Merging #6897 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #6897   +/-   ##
=======================================
  Coverage   66.98%   66.98%           
=======================================
  Files         250      250           
  Lines       10358    10358           
  Branches        3        3           
=======================================
  Hits         6938     6938           
  Misses       3419     3419           
  Partials        1        1

Impacted Files	Coverage Δ
packages/jest-jasmine2/src/is_error.js	0% <ø> (ø)	⬆️

---

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[natealcedo]

Hey @Pajn, I'm not a core contributor on this project so take my advice with a grain of salt, but here's my 2 cents. I suggest you go down the path of writing an end to end test for this. I've tried this locally with your changes and this test works.

This file is located jest/e2e/__tests__/promise_reject.test.js and I have a folder named jest/e2e/promise-reject

/**
 * Copyright (c) 2014-present, Facebook, Inc. All rights reserved.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @flow
 */

'use strict';

import runJest from '../runJest';
import path from 'path';
const {cleanup, writeFiles} = require('../Utils');

const DIR = path.resolve('../promise-reject');

beforeEach(() => cleanup(DIR));
afterEach(() => cleanup(DIR));

test('', () => {
  writeFiles(DIR, {
    'package.json': '{}',
    'promise_reject.test.js': `
      test('test', () => {
        return Promise.reject(null)
      });
    `,
  });

  const {stdout, stderr, status} = runJest(DIR);

  expect(stdout).toBe('');
  expect(stderr).toMatch(/Failed: null/);
  expect(status).toBe(1);
});

Perhaps one of the senior contributors can weigh in on this?

[SimenB]

You can do JEST_CIRCUS=1 yarn jest ... to run the test with circus (the CI failure). It should be a matter of normalizing the output before the assertion.

---

Thanks for weighing in @natealcedo!

[natealcedo]

Hey @Pajn, do you still wanna work on this? I don't mind carrying on from here :)

[Pajn]

Sorry, I forgot to update here and then forgot the whole issue.

I had trouble finding where to make the change. Please take over if you want as you probably can navigate the code much better than I.

[github-actions]

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