Jest, mocking return from await, I see results in console, but expect still fails-CodePudding

I have a pretty simple example of a mock working, updating the value correctly, but my test still fails.

fetchStuff.js:

const fetchStuff = async (entity, service) => {
    entity = await service.get();
    console.log('entity is an expected result!', entity); // this consoles out the expected value correctly.
}

fetchStuff.spec.js:

it('should...', () => {
    const expected = 'this will show up in console';
    const service.get = jest.fn().mockImplementation(() => expected);
    let entity;

    fetchStuff(entity, service);

    expect(entity).toEqual(expected) // entity = 'undefined'
});

Every time, I see that console.log in the function is printing out the expected result, but some reason the expect(entity) is always undefined.

I've tried stuff like with flush-promise, I've tried removing the await. I've even seen the done(), technique, where we pass done in to it, ie it('should...', done => {...})

Not sure why I cannot get the correct expected, even tho the console is showing the expected result.

PS. I understand this is not respecting functional paradigm or pure functions. Please ignore that.

CodePudding user response：

You are using an asynchronous function, but testing right away, before the promise is resolved. You need an async/await in your test, if you are using asynchronous calls, like your await in the main function.

it('should...', async () => {
    const expected = 'this will show up in console';
    const service.get = jest.fn().mockImplementation(() => expected);
    let entity;

    await fetchStuff(entity, service);

    expect(entity).toEqual(expected) // entity = 'undefined'
});

However, as per the comment on your question, the code may not be returning what you expect, so this change for async/await will not solve the problem on its own.

const fetchStuff = async (entity, service) => {
    entity = await service.get();
    console.log('entity is an expected result!', entity); 
    return entity;
}


it('should...', async () => {
    const expected = 'this will show up in console';
    const FakeService = jest.fn().mockResolvedValue(expected),

    const entity = await FakeService();
    expect(entity).toBe(expected) ;
});