jest: [Bug]: "mockImplementation" is behaving different than the syntacical-sugar version"mockResolvedValue"

Version

27.5.1

Steps to reproduce

Repro:

const testMock = {
    works: jest.fn().mockImplementation(() => Promise.resolve(undefined)),
    fails: jest.fn().mockResolvedValue(undefined),
};

it('test-mockResolvedValue', fakeAsync(async() => {
    await testMock.fails();
    flush();
    expect(true).toBeTrue();
}));

it('test-mockImplementation', fakeAsync(async() => {
    await testMock.works();
    flush();
    expect(true).toBeTrue();
}));

Expected behavior

Both tests are passing without any error, since both should be exactly the same as the Jest-docs are stating that mockFn.mockResolvedValue(value) is “Syntactic sugar function for” jest.fn().mockImplementation(() => Promise.resolve(value)).

Actual behavior

Test test-mockResolvedValue fails on the flush() due to The code should be running in the fakeAsync zone to call this function:

Additional context

I feel this problem is linked to https://github.com/facebook/jest/issues/6645 and https://github.com/facebook/jest/issues/11146 .

Environment

System:
    OS: Windows 10 10.0.19043
    CPU: (12) x64 Intel(R) Core(TM) i7-10850H CPU @ 2.70GHz
Binaries:
    Node: 16.16.0 - C:\Program Files\nodejs\node.EXE
    npm: 8.11.0 - C:\Program Files\nodejs\npm.CMD
npmPackages:
    jest: ^27.2.3 => 27.5.1

About this issue

Original URL
State: closed
Created 2 years ago
Reactions: 2
Comments: 37 (3 by maintainers)

Most upvoted comments

I can now confirm it has to do with https://github.com/facebook/jest/issues/6645 :

const testMock = {
    works: jest.fn().mockImplementation(() => Promise.resolve(undefined)),
    fails: jest.fn().mockResolvedValue(undefined),
};

it('test-mockImplementation', fakeAsync(async() => {
    console.log(new Promise(() => null) instanceof Promise); // true
    console.log(testMock.works() instanceof Promise); // true
    console.log(testMock.fails() instanceof Promise); // FALSE
    expect(true).toBeTrue();
}));

The mockResolvedValue() does NOT return a normal/real Promise, which buggs out ngZone.

mhombach on Sep 2, 2022

Issue still needs a fix.

mhombach on May 28, 2023

@mhombach please give https://github.com/facebook/jest/releases/tag/v29.2.2 a try 🙂

SimenB on Oct 24, 2022

I confirm this should be fixed. This is very hard to debug as nothing indicates mockResolved or mockReject could have a different behavior.

For example, waiting for a next tick would finish the promises with mockImplementation but not with mockResolved or mockReject.

yannbriancon on Oct 24, 2022

Any chance this issue will be verified and tackled? It’s an easy reproducible bug which should be also somewhat-eaasy to fix.

mhombach on Sep 30, 2022

Issue is not fixed yet. Seriously, this issue is now open for almost 1 full year and it’s ignored?

mhombach on Jun 27, 2023

Issue is not fixed yet. Seriously, this issue is now open for over half a year and it’s ignored?

mhombach on Mar 27, 2023