Testing dispatched actions in Redux thunk with Jest

Question

I'm quite new to Jest and admittedly am no expert at testing async code...

I have a simple Fetch helper I use:

export function fetchHelper(url, opts) {
    return fetch(url, options)
        .then((response) => {
            if (response.ok) {
                return Promise.resolve(response);
            }

            const error = new Error(response.statusText || response.status);
            error.response = response;

            return Promise.reject(error);
        });
    }

And implement it like so:

export function getSomeData() {
    return (dispatch) => {
        return fetchHelper('http://datasource.com/').then((res) => {
            dispatch(setLoading(true));
            return res.json();
        }).then((data) => {
            dispatch(setData(data));
            dispatch(setLoading(false));
        }).catch(() => {
            dispatch(setFail());
            dispatch(setLoading(false));
        });
    };
}

However I want to test that the correct dispatches are fired in the correct circumstances and in the correct order.

This used to be quite easy with a sinon.spy(), but I can't quite figure out how to replicate this in Jest. Ideally I'd like my test to look something like this:

expect(spy.args[0][0]).toBe({
  type: SET_LOADING_STATE,
  value: true,
});


expect(spy.args[1][0]).toBe({
  type: SET_DATA,
  value: {...},
});

Thanks in advance for any help or advice!

Answer 1

The redux docs have a great article on testing async action creators:

For async action creators using Redux Thunk or other middleware, it's best to completely mock the Redux store for tests. You can apply the middleware to a mock store using redux-mock-store. You can also use fetch-mock to mock the HTTP requests.

import configureMockStore from 'redux-mock-store'
import thunk from 'redux-thunk'
import * as actions from '../../actions/TodoActions'
import * as types from '../../constants/ActionTypes'
import fetchMock from 'fetch-mock'
import expect from 'expect' // You can use any testing library

const middlewares = [thunk]
const mockStore = configureMockStore(middlewares)

describe('async actions', () => {
  afterEach(() => {
    fetchMock.reset()
    fetchMock.restore()
  })

  it('creates FETCH_TODOS_SUCCESS when fetching todos has been done', () => {
    fetchMock
      .getOnce('/todos', { body: { todos: ['do something'] }, headers: { 'content-type': 'application/json' } })


    const expectedActions = [
      { type: types.FETCH_TODOS_REQUEST },
      { type: types.FETCH_TODOS_SUCCESS, body: { todos: ['do something'] } }
    ]
    const store = mockStore({ todos: [] })

    return store.dispatch(actions.fetchTodos()).then(() => {
      // return of async actions
      expect(store.getActions()).toEqual(expectedActions)
    })
  })
})

Their approach is not to use jest (or sinon) to spy, but to use a mock store and assert the dispatched actions. This has the advantage of being able to handle thunks dispatching thunks, which can be very difficult to do with spies.

This is all straight from the docs, but let me know if you want me to create an example for your thunk.