How to test an async action (by monkeypatching the dispatch function)

asyncActionSpec.js

/* async-action.js */
import SomeService from './some-service';

export function doAsync(arg) {
  return dispatch => {
    // SomeService.doSomething returns a promise which resolves to the passed argument
    SomeService.doSomething(arg).then(result => {
      const action = { type: 'ASYNC_SUCCESS', payload: result };
      dispatch(action);
    }).catch(error => {
      const action = { type: 'ASYNC_FAILED', payload: error, error: true };
      dispatch(action);
    });
  };
}

/* async-action.spec.js */
const doAsync = proxyquire('./async-action.js', {
  // Mock the EchoService:
  './some-service': {
    doSomething(value) { return Promise.resolve(value); }
  }
});

describe('Async action', () => {
  it('should dispatch ASYNC_SUCCESS on success', (done) => {
    const dispatch = (action) => {
      expect(action.type).to.be('ASYNC_SUCCESS');
      expect(action.payload).to.be('hello');
      done();
    };
    doAsync('hello')(dispatch);
  });
});