Testing promise with stub

Question

I'm trying to do some tests with chai using sinon stub. The thing is, I'm stubbing my fetch like this and resolving my promise.

  let fetchedStub;

  beforeEach(() => {
    fetchedStub = sinon.stub(global, 'fetch');
    fetchedStub.resolves({ json: () => { body: 'json' } });
  });

Then I'm testing if my data is returning correctly

it('should return the JSON data from the promise', () => {
  const result = search('test');
  result.then((data) => {
    expect(data).to.be.eql({ body: 'json' });
  });
});

But instead of passing the test, I'm getting

TypeError: Cannot read property 'then' of undefined

Am I doing something wrong with my promise? I think I need some light here.

Edit: this is the search function.

    export const search = (query) => {
  fetch(`https://api.spotify.com/v1/search?q=${query}&type=artist`)
    .then(data => data.json());
};

ghybs ghybs · Accepted Answer · 2021-02-22T20:23:37

Your search arrow function does not return anything, hence in your test result is undefined, hence the error message.

You should simply return the result of your fetch:

export const search = (query) => {
  // return something
  return fetch(`url`).then(data => data.json());
};

You might have been confused by the arrow function shorthand syntax, which automatically returns the result of a single expression, provided that it is not wrapped in curly braces:

export const search = (query) => fetch(`url`).then(data => data.json()); // no curly braces after the arrow

Testing promise with stub

1 Answers