How do you mock the resolved value of an awaited dispatch

Question

Let's say I have a thunk:

import fetchSomeData from '/path/to/fetchSomeData'

const myAction = () => async dispatch => {
    ...
    const data = await dispatch(fetchSomeData()) // `fetchSomeData` is itself a thunk
    ...
}

And in my test file, I want to specify what the data is I want the fetchSomeData function to return:

import fetchSomeData from '/path/to/fetchSomeData'
import myAction from '/path/to/myAction'

jest.mock('/path/to/fetchSomeData')

describe('test function', () => {
    beforeEach(() => { jest.clearAllMocks() })

    it('tests the function', async () => {
        const dispatchMock = jest.fn()
        fetchSomeData.mockResolvedValueOnce({ value: 'some dummy data' })

        await myAction()(dispatchMock)

        expect(dispatchMock).toHaveBeenCalledTimes(1)
    })
})

However, when doing this, the data that I'm expecting to be my dummy data, always comes back as undefined.

What am I doing wrong?

In our package.json, we have jest 27.5.1 and babel-jest 27.1.0

Answer 1

Because the dispatch function is mocked. You should use the real implementation of store.dispatch.

e.g.

fetchSomeData.js:

const fetchSomeData = () => {};
export default fetchSomeData;

index.js:

import fetchSomeData from './fetchSomeData';

const myAction = () => async (dispatch) => {
  const data = await dispatch(fetchSomeData());
  console.log(' ~ myAction ~ data:', data);
};

export default myAction;

index.test.js:

import fetchSomeData from './fetchSomeData';
import myAction from '.';
import { createStore, applyMiddleware } from 'redux';
import thunk from 'redux-thunk';

jest.mock('./fetchSomeData');

describe('test function', () => {
  beforeEach(() => {
    jest.clearAllMocks();
  });

  it('tests the function', async () => {
    fetchSomeData.mockReturnValue({ type: 'FETCH_SOME_DATA', value: 'some dummy data' });

    const mockStore = createStore(() => {}, applyMiddleware(thunk));
    const dispatchSpy = jest.spyOn(mockStore, 'dispatch');

    await myAction()(mockStore.dispatch);

    expect(dispatchSpy).toHaveBeenCalledTimes(1);
  });
});

Test result:

> jest -o

  console.log
     ~ myAction ~ data: { type: 'FETCH_SOME_DATA', value: 'some dummy data' }

      at stackoverflow/78234718/index.js:5:11

 PASS  stackoverflow/78234718/index.test.js
  test function
    √ tests the function (18 ms)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        1.981 s, estimated 2 s
Ran all test suites related to changed files.

package versions:

"redux-thunk": "^2.4.2",
"redux": "^4.2.1",