testing redux thunk middleware

actions.js

export const doTheThing = () => (dispatch, getState) => {
  const users = getState();
  dispatch({
    type: 'THE_THING',
    users,
  });
};

test.js

import expect from 'expect';



describe('doTheThing', () => {
  
  it('should return a function', () => {
    expect(doTheThing()).toBeA('function');
  })
  
  it('dispatch a doTheThing action', () => {
    const getState = () => ({users: 'foo'});
    const dispatch = expect.createSpy();
    doTheThing()(dispatch, getState);
    expect(dispatch).toHaveBeenCalledWith({type: 'THE_THING', users: 'foo'});
  })
  
});

It is worth noting that first test becomes redundant with the 2nd.

You should keep in mind that this approach will only work if dispatch() is called synchronously. If it is called asynchronously, it will do the expect(dispatch)... before dispatch has actually been called ;)

I wrote something similar, but promise-based to care for my asynchronous use case. The problem about my approach is that it will only work properly if you dispatch() once, since the promise will resolve after the first call...

PS: This might also be useful! reduxjs/redux#546