Util for testing thunks from redux-thunk using expect

mock-thunk.js

import expect from 'expect' // using expect by @mjackson

export default (state) => {
  const spy = expect.createSpy()
  const getState = () => state
  const dispatch = (action) => typeof action === 'function'
    ? action(dispatch, getState)
    : spy(action)
  return {spy, getState, dispatch}
}

thunks.js

import {addUser} from './actions'

/*
  Thunk to be tested
*/

export const submitForm = (info) => (dispatch, getState) => {
  const user = getUser(getState())
  if (user) {
    fetch(FETCH_BODY)
      .then((userId) => dispatch(addUser(userId)))
  } else {
    dispatch(errorMessage('no user defined'))
  }
}

thunks.test.js

import mockThunk from './mock-thunk'
import {submitForm} from './thunks.js'
import mockState from 'path'


/*
  As thunks can read the store, we need to mock it up as well
*/

describe('submitForm', () => {
  it('dispatches addUser when user is defined', () => {
    const state = mockState()
    const INFO = 'FORM_INFO'
    const {spy, dispatch} = mockThunk(state)
    dispatch(submitForm(INFO))
    
    expect(spy).toHaveBeenCalledWith(addUser(INFO))
  })

  it('dispatches error message when user is not defined', () => {
    const state = mockState()
    const INFO = 'FORM_INFO'
    const {spy, dispatch} = mockThunk(state)
    dispatch(submitForm(INFO))
    
    expect(spy).toHaveBeencalledWith(errorMessage('no user defined'))
  })
})