CODEWITHSUNDEEP
reactjsjestjsenzyme
Shibasis Sengupta
Shibasis Sengupta

Reputation: 649

testing a jest mock function itself

I was trying to test a mock function by printing its return value on console. This is the setup -

The Service which is being mocked (just a copy of Fetch)-

export default function FetchService(url){
return fetch(url);
}

This is my mock function setup (inside the__mocks__ folder) -

const  posts= [
      { "id": 1, "Name": "pen", "Stock": "100" },
      { "id": 2, "Name": "pencil", "Stock": "150" }
    ]


export default  function FetchService(url){
return  new Promise((resolve)=>{
Promise.resolve(posts)
})
     }

So if I the mock function works fine, the promise should resolve and always return the predefined array of 2 objects, right?

Keeping that in mind, I wrote the following test case -

jest.mock('./FetchService');
test('getting data',(done)=>{

    let returnedData=[];
    FetchService('').then((data)=>data.json()).then((dataP)=>{
        returnedData=dataP;     
    });

    setTimeout(()=>{console.log(returnedData);done();},2000);    
})

Problem is , the the consoloe.log shows that the 'returnedData' is empty array instead of what I expected.

What am I missing here? Please let me know if I can provide some more info.

Upvotes: 1

Views: 852

Answers (1)

Sasha
Sasha

Reputation: 5944

At first your mock is never resolved, because you don't call passed resolve callback, and second is that mock should return object with json method, which should return promise:

export default  function FetchService(url) {
  const json = () => Promise.resolve( posts );
  return  new Promise( resolve => resolve({ json }));
}

Also, you can call done() directly in .then (maybe just simpler without setTimeout):

test('getting data',(done)=>{
  FetchService('')
    .then(data => data.json())
    .then(
      data => {
        expect(data).toHaveLength(2);
        done();     
  });
})

Upvotes: 1

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