"Modern" fake-timer implementation doesn't work with PromiseJS.

Awesome work on https://github.com/facebook/jest/pull/7776, thanks for that!!

🐛 Bug Report

I’m using Jest 26.1.0.

Testing async code with Promises, as described in this Jest doc, doesn’t seem to work with jest.useFakeTimers('modern'); (from https://github.com/facebook/jest/pull/7776; documented here) if you’re using the ‘promise’ library from NPM.

For a while (starting in https://github.com/facebook/react-native/commit/3ff39870ce776c653823e1733363be0401896294), React Native has used that library as part of their Jest setup (which you get if you use preset: 'react-native'), so I expect this will affect most people using React Native (this is how I encountered it).

Otherwise, I’m not sure how often people use that ‘promise’ library, but it’s an official solution given in a Jest troubleshooting doc, and pops up as a workaround for some issues in this repo (e.g. here).

This is arguably a regression (or would be when ‘modern’ becomes the default), as this behavior isn’t observed with jest.useFakeTimers('legacy'); or jest.useRealTimers().

To Reproduce

E.g.,

global.Promise = require('promise');

jest.useFakeTimers('modern');

test('1 equals 1', async () => {
  await Promise.resolve();
  expect(1).toEqual(1);
});

Expected behavior

I expect the test to pass. Instead, five seconds go by and I get this failure:

  ✕ 1 equals 1 (5006 ms)

  ● 1 equals 1

    : Timeout - Async callback was not invoked within the 5000 ms timeout specified by jest.setTimeout.Timeout - Async callback was not invoked within the 5000 ms timeout specified by jest.setTimeout.Error:

      3 | jest.useFakeTimers('modern');
      4 | 
    > 5 | test('1 equals 1', async () => {
        | ^
      6 |   await Promise.resolve();
      7 |   expect(1).toEqual(1);
      8 | });

      at new Spec (node_modules/jest-jasmine2/build/jasmine/Spec.js:116:22)
      at Object.<anonymous> (fetchData.test.js:5:1)

Test Suites: 1 failed, 1 total
Tests:       1 failed, 1 total
Snapshots:   0 total
Time:        5.762 s, estimated 6 s
Ran all test suites.
error Command failed with exit code 1.

Link to repl or repo (highly encouraged)

In the repro linked below, I’ve closely imitated all the tests from the sections in the “Testing Asynchronous Code” doc that use Promises, to suggest that the failure happens in usual, well-documented ways of testing (provided you’re using PromiseJS).

In its current state, you should observe these timeout errors on tests that use Promises (just run yarn and yarn test).

Try uncommenting global.Promise = require('promise'); at the top of fetchData.test.js; the tests should all pass.

Try doing something other than jest.useFakeTimers('modern');; the tests should all pass.

(Incidentally, note that accidentally calling jest.useFakeTimers multiple times with different arguments in the same file seems disruptive and might hamper your investigation. Also, be sure to comment out jest.runAllTimers() if you’re using real timers.)

https://github.com/chrisbobbe/jest-async-modern-timers-repro

envinfo

  System:
    OS: macOS 10.15.5
    CPU: (12) x64 Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
  Binaries:
    Node: 10.20.1 - ~/.nvm/versions/node/v10.20.1/bin/node
    Yarn: 1.22.4 - /usr/local/bin/yarn
    npm: 6.14.4 - ~/.nvm/versions/node/v10.20.1/bin/npm
  npmPackages:
    jest: ^26.1.0 => 26.1.0 

[Hedi-s]

I have the same error with nock 12.0.3 and jest 26.1.0

The test case

test('nock', async () => {
    jest.useFakeTimers('modern');
    nock('http://modern').get("/").reply(200);
    await fetch(`http://modern`, { method: "GET" });
});

Failing :

 : Timeout - Async callback was not invoked within the 5000 ms timeout specified by jest.setTimeout.Timeout - Async callback was not invoked within the 5000 ms timeout specified by jest.setTimeout.Error:
  > 18 |         test('nock', async () => {
    |         ^
    19 |             jest.useFakeTimers('modern');
    20 |             nock('http://modern').get("/").reply(200);
    21 |             await fetch(`http://modern`, { method: "GET" });

It’s working when I replace

• ‘modern’ by ‘legacy’ or
• fetch(…) by Promise.resolve() (nock is not actually used)

[deimantasa]

Is this moving along? As issue still persists.